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[Seminar] [Android Apps (Now with Jelly Beans!)]

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[Jordan Jozwiak] [Harvard University]

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[This is CS50.] [CS50.TV]

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>> Hello everyone, and welcome to the Android Apps (Now with Jelly Beans!) Seminar.

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It's called Now with Jelly Beans, of course, because 

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the latest version of the OS is called Jelly Bean. 

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When I talked about Android last year and did this basically same seminar

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I was presenting the design patterns and stylistic choices for Gingerbread,

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even though Ice Cream Sandwich had come out at the time, 

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and this is something we'll talk about going forward a little bit.

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Android, of course, has some issues with fragmentation,

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so the latest Google operating system is usually

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not really going to become common among the users for potentially up to a year, unfortunately.

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>> But disregarding that, we'll talk about plenty of reasons why

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Android is much better than iOS.

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Okay, we'll talk about Android versus iOS,

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some design paradigms, how you'll get set up in just one slide,

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and the big difference between this and last year is I just want to 

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zoom through some conceptual things working with

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the operating system and then go into a really basic example.

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In fact, just the example that Google describes for building your first app,

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and we'll go through it together and just describe.

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>> I know many of you have only coded in C, so Java is already going to be 

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a different perspective, and this way you'll get your feet wet

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and feel a little more comfortable with it hopefully.

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A quick summary, Android versus iOS.

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In Android there's this one-time developer fee of $25, 

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none of this $100 per year thing.

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There are no restrictions, which means that if I want to submit an app,

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I just submit it, and there's no approval process like there is for iOS.

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You get to develop with Java using Eclipse,

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which is cross platform, so it doesn't matter if you have a Mac, 

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Windows, or some Linux machine.

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Of course, with iOS you have to use XCode on a Mac,

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and Android is used by many more people,

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so if you want your app to have some sort of visibility or perhaps

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make a little money from advertisements

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you're probably more likely to benefit from Android.

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>> And one thing that's always been known about Android 

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is the extreme amount of customization, whereas iOS is very fixed in their ways

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so that they can maintain security and control over every little aspect

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of the design within their OS and the individual apps.

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Android is very free form, and there's so many more possibilities.

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Okay, some design paradigms.

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Notice here just like iOS has tablets and iPhones and iPod Touches

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they have to support, say, like a dozen devices if you want to support 

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historical things as well.

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With Android you have to support hundreds of devices,

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so there are some things that Google has been trying to implement

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to make the user experience a little more consistent,

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but we'll also talk about how this means that there are issues of fragmentation

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that you constantly have to be aware of supporting.

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Fragmentation means that there are many different operating systems,

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many different phones with different hardware running Android all at the same time,

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so this graph here goes back for about 6 months.

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Yeah, 6 months, and you can see how the darkest band

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on the bottom is Jelly Bean, which came out over the summer,

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and you can see right now probably about 2% of the phones have it.

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>> Ice Cream Sandwich came out over a year ago,

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and a quarter of the phones have it.

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There are still a lot of phones that are using OS version from years ago.

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One thing that Google has tried to do to make the user experience 

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a lot more consistent across apps is starting with Honeycomb, 

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which is the tablet version, then Ice Cream Sandwich and Jelly Bean,

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they're really trying to emphasize use of this action bar, 

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which is what you can see at the top here,

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everything right here, including this little settings button.

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It's the design choice.

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Now, whenever you see the 3 dots it means click on this,

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and there will be a drop-down menu, which has some sort of settings.

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This only shows up because I clicked on this button.

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This is something that they're trying to use to make apps a little more consistent

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across the board and so the user has a better sense of uniform experience.

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>> Okay, so in case you haven't done this already or if you're watching at home

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then you can follow these steps to set up your coding environment.

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It will involve going to the website here.

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You can Google installing Android SDK

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and follow some descriptions there.

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They tell you everything.

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They have you install the SDK, download Eclipse Classic version,

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even though, of course, we're coding in Java.

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They recommend this one, and then this ADT, the Android Development Tools,

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is a plugin that you install into Eclipse which allows you to

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have a much more streamlined experience with Android within Eclipse.

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It will give you some graphical user interfaces 

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for designing the views, and it will give you much more support

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and the ability to launch with the emulator and all that sort of thing.

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Application framework.

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>> I want to talk about how the projects within Android are structured,

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and then we'll go into a quick example, and hopefully 

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you can ask questions at any point and feel comfortable by the end of it.

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We have some jargon first.

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An activity is like the screen you see when you launch an app.

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The entire experience is the activity itself, 

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so you could think of it as a screen or a view,

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but it's actually the source code side of it.

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We still call the actual interface part of it a view.

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It's sort of like how in pset 7 we had the controller and then the view.

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The activity is more or less the controller,

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and the view is what we're doing in terms of the XML

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that is associated with that activity.

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Fragments are something that's implemented in Ice Cream Sandwich going forward.

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It's just an idea of taking parts of the view or the activity

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and dividing them into separate areas so that we can

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make our code more usable for these many different devices

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that we have to support, and it's just a way of trying to

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also factor out more code.

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Services are background things like playing music or navigation directions potentially.

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Content providers, these are APIs within the operating system

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that allow you to access shared data such as contact information,

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and then an intent is something we'll use when we want to launch

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a new activity from our current activity.

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>> Hello Android, this is going to be a project that we'll talk about.

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I'll actually do it for you, and then we'll do a thing where we click a button

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with some text and launch a new activity.

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Very straightforward, but I want to go through

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what will go into a project like this.

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When you make the new project you'll see within Eclipse

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there's this project called Hello Android.

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Then there are a whole bunch of folders here.

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The ones you're really concerned with are the source folder,

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the resource folder, the res, and to some extent the libs folder for libraries.

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And just so we're on the same page with that

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if you were to create a new project,

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you can do this right here, so if I want to call it HelloAndroid,

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and then it automatically does a whole bunch of the information for us.

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The package name is supposed to be a unique identifier 

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that would normally be associated with the website, if you had one.

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>> For example, I will call this net.cs50.helloandroid.

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And I already have made this project once.

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Okay, sorry. Let's call it HelloCS50.

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And then it will ask things like what sort of icon do we want to make.

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This is all because of the Android Developer Tools interface,

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the plugin that we added to Eclipse, so we can choose things like 

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what icon we want, and that would go into that depth if we want.

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But in the end, just make the project,

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and everything shows up right here.

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As I showed on the other screen,

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we have the source folder, and I'll talk about what all this means soon,

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but you can see that immediately it takes us to the HelloCS50 screen.

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There are some buttons over here for adding text and text field layouts.

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It's sort of like XCode but unfortunately not quite as streamlined.

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But the clips will be your friend and ADT in particular for doing this.

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>> Okay, the source folder is where 

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the Java files are held, and this is actually the launch of your program.

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It's basically like the controllers.

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The resource folder or the res is where we'll keep screen layouts,

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images, sounds, text, animation and everything else, libs, obviously, libraries.

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And the Manifest, it's the way that the Android system knows

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how to interact with your app.

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It tells it about permissions and what activities will actually be run.

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It's all the essential information that's necessary to run  your app.

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The source folder is—if we expand it as you can see right here.

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And an example that a code would look—this is the default code.

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As we called it, MainActivity.

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By default, we get onCreate, which is a function that's called when this activity loads,

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so you want to call onCreate (savedInstanceState).

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This will restore any bits of information

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in case the app was paused.

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>> There's a whole activity life cycle chart which you can look at

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when you get a little more in-depth in it, 

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but the most important line of code there is this setContentView function 

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which will load the resource file for the layout.

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Then what onCreate here is basically doing is it's saying

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when I create this activity I want to load this layout.

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And we'll talk about what that layout is in a second.

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If we were to launch that here it looks exactly like this,

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and by default because we have Eclipse doing this and ADT doing it for us

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this is all boilerplate code that's created for us,

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and we can move on and change things as we like.

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The resource folder, like I said, this is where we hold all layouts,

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drawables in terms of any sort of images—

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they're called drawables—and then sound files, menus.

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It's a way of a whole bunch of XML in a nice sorted fashion.

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As you can see, there are .hdpi, ldpi, mdpi and xhdpi folders for the drawables.

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These are different screen densities, so high density pixel per inch,

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low density, medium density, extra high density.

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>> This is, again, so we can support all these different devices,

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and ideally, you will have different images for each different resolution.

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Layouts are where we include all the different layouts that will be used in different activities.

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They could also include layouts for fragments,

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which means partial activities basically.

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If you want to do something cool like whenever you rotate the phone

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you want it to have a different layout you can do layout-landscape as a different folder,

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and Android automatically has a whole bunch of these rules within the resource folder,

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so it will know to look at different folders based on the current setup of the phone,

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what sort of hardware you're using.

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Similarly, this values-v11 here and values-v14

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and the default values folder this is for—

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well, values by itself, this will be the default values across all versions of the operating system.

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On the other hand, v11 and v14 correspond with Honeycomb 

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and Ice Cream Sandwich, respectively.

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Again, these are ways that—within these folders are different strings

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and styles, so you can customize the appearance of your app

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or potentially even its functionality, although that would probably be a bad idea,

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based on the version of the operating system.

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>> And I talked about all this here.

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Again, drawable, raw, layout, values.

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The defaults, if we go into Hello Android or Hello CS50 right now

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it will look just like this.

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It will say hello world.

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As you can see right here with the Android text

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the text for this text view, which is basically just a label,

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is what we would call it in iOS.

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It has this funny notation @string/hello_world.

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This is so we can—we attempt to extract all of the strings,

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all of the hard-coded strings in Android into a separate folder,

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which happens to be in values.strings.

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If we look here, we can see that we have a hard-coded string saved here

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for hello world, and it's called hello world, and this is sort of a 

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common design decision across many platforms that you want to—

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strings are the sort of things that we want to potentially be able to change.

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We don't want to control F in our source code file in our XML.

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We want to be able to change this whenever we get the chance.

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>> This XML file, strings.xml, is a way of extracting

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hard-coded strings that would otherwise be in our layout resources

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or in our source code.

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The Manifest is where we keep this essential information about the application.

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It includes the package name. That has to be a unique identifier.

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Unlike the App Store for iOS the names of the applications

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don't have to be unique, and you can in fact change the name of your application

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after you submit it, so if I start out with Angry Birds,

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and then I make an update, and I don't want to release a new version

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I guess I could call it Angry Birds 2 while I'm on the same release cycle.

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It would just show up as an update.

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The only thing that has to be unique is this package name,

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which not many people will see.

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Well, you'd only see if you were looking at the source code or if there is some sort of error.

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The components include activities, so we have to declare

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any sort of activity we use.

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This is a permission sort of thing.

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>> Because Android doesn't have this rigorous application process

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for submitting apps instead they just do everything based off of permissions

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and declaring things in the Manifest.

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The SDK version is also important.

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We can set use as SDK minimum version something.

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Obviously, you want to create code

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and design for the newer operating systems.

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00:16:18,570 --> 00:16:20,840
Perhaps not the newest, maybe not Jelly Bean.

240
00:16:20,840 --> 00:16:23,610
Maybe you want to design primarily for Ice Cream Sandwich,

241
00:16:23,610 --> 00:16:27,120
although they are pretty much the same in terms of design decisions

242
00:16:27,120 --> 00:16:30,550
and the actual libraries and APIs.

243
00:16:30,550 --> 00:16:36,250
But rather than have people 

244
00:16:36,250 --> 00:16:40,050
of the original Android version—like Donut way back when—

245
00:16:40,050 --> 00:16:43,420
who still happen to be using that try to download your application and then say

246
00:16:43,420 --> 00:16:46,160
it doesn't work on my phone you can set the minimum version

247
00:16:46,160 --> 00:16:48,620
and have it be Gingerbread or Ice Cream Sandwich 

248
00:16:48,620 --> 00:16:53,300
or whatever you feel comfortable submitting.

249
00:16:53,300 --> 00:16:57,170
And this is an example of the Manifest. We can look at the actual one in a bit.

250
00:16:57,170 --> 00:17:00,900
>> Okay, we'll just go forward with the demo now.

251
00:17:00,900 --> 00:17:08,900
This is the demo if you Google Android build your first app or something like that.

252
00:17:08,900 --> 00:17:12,089
We'll go through everything that's going on in there,

253
00:17:12,089 --> 00:17:17,690
and sorry, just for a reference who here knows Java to any extent?

254
00:17:17,690 --> 00:17:28,310
Okay, so Java is new coding language for most people coming out of CS50.

255
00:17:28,310 --> 00:17:31,850
Briefly, to go over again what it says here,

256
00:17:31,850 --> 00:17:35,580
what we want to do is rather than adjust this hello world application

257
00:17:35,580 --> 00:17:38,620
that all it does is it launches and it says hello world

258
00:17:38,620 --> 00:17:43,580
and it says hello CS50 at the top because that's the activity name

259
00:17:43,580 --> 00:17:47,190
we're going to attempt to make a text field and a button

260
00:17:47,190 --> 00:17:50,680
so that when we press this button it will take the text

261
00:17:50,680 --> 00:17:53,660
from the text field and launch a new activity, and it will say 

262
00:17:53,660 --> 00:17:58,380
whatever that text said in the activity, and this is relatively simple.

263
00:17:58,380 --> 00:18:00,650
It's not very interesting. You wouldn't want to release any app like this.

264
00:18:00,650 --> 00:18:03,880
But it demonstrates some important design things.

265
00:18:03,880 --> 00:18:07,030
>> We'll have to interact with the Manifest, with the layout files,

266
00:18:07,030 --> 00:18:12,440
with the source code, and you can see how to launch one activity from another.

267
00:18:19,740 --> 00:18:23,060
We'll start with the layout for our first activity,

268
00:18:23,060 --> 00:18:27,320
which I know it's kind of small, 

269
00:18:27,320 --> 00:18:32,660
but as you can see right now, all it is is it has our logo that we created,

270
00:18:32,660 --> 00:18:36,310
the activity name, and it says hello world in the center.

271
00:18:36,310 --> 00:18:40,400
Instead, I'm first going to make this into a linear layout,

272
00:18:40,400 --> 00:18:42,350
a relative layout, and these are all things 

273
00:18:42,350 --> 00:18:45,870
you could look up and are worth going over at some point in terms of the layouts.

274
00:18:45,870 --> 00:18:47,310
It's a lot like HTML.

275
00:18:47,310 --> 00:18:52,640
We said it's not really worth knowing in terms of a programmatic sense,

276
00:18:52,640 --> 00:18:55,840
but there are so many different layouts you can control,

277
00:18:55,840 --> 00:18:57,970
and it's just like CSS in terms of styles.

278
00:18:57,970 --> 00:19:01,590
>> There's a lot going on just in terms of the aesthetics here,

279
00:19:01,590 --> 00:19:08,930
and yeah, it's worth learning, but it's the sort of thing you should look up

280
00:19:08,930 --> 00:19:11,810
as you go and you feel like you need something new.

281
00:19:11,810 --> 00:19:17,030
I can take advantage of some of the ADT tools here at least to start off with.

282
00:19:17,030 --> 00:19:21,930
I'll make a text field, and I will make a button. 

283
00:19:21,930 --> 00:19:24,100
Put them right next to each other.

284
00:19:24,100 --> 00:19:28,200
They already resize appropriately.

285
00:19:28,200 --> 00:19:31,320
Sorry, again, coming back to the difference between linear layout and relative layout,

286
00:19:31,320 --> 00:19:34,830
a linear layout gives a little more functionality

287
00:19:34,830 --> 00:19:38,720
in terms of filling space and making sure

288
00:19:38,720 --> 00:19:42,790
we position things horizontally or vertically.

289
00:19:42,790 --> 00:19:46,130
The big difference between a linear layout and a relative layout

290
00:19:46,130 --> 00:19:50,250
is the relative layout positions everything relative to other views,

291
00:19:50,250 --> 00:19:52,630
and the good thing about it is that it takes less time to draw

292
00:19:52,630 --> 00:19:56,120
because the operating system looks at all the code and says this goes

293
00:19:56,120 --> 00:19:58,270
relative to this here, here.

294
00:19:58,270 --> 00:20:03,170
It means it makes fewer measurements than a whole bunch of nested linear layouts,

295
00:20:03,170 --> 00:20:06,840
which I would have to do if I wanted things to go vertically here.

296
00:20:06,840 --> 00:20:10,510
>> I already have some things going horizontally, so I would need a different linear layout

297
00:20:10,510 --> 00:20:14,560
to nest them vertically, but if I were doing a relative layout I could say

298
00:20:14,560 --> 00:20:18,140
keep this to the left, this to the right and these things below.

299
00:20:18,140 --> 00:20:21,850
But because I want them to fill right now I'm going to use a linear layout,

300
00:20:21,850 --> 00:20:24,510
and you can see it already does a lot of these things for us.

301
00:20:24,510 --> 00:20:28,890
All views need to have a property of width and height,

302
00:20:28,890 --> 00:20:33,410
and this happens to have a weight of 1, and this has a weight of 1

303
00:20:33,410 --> 00:20:36,050
so that it fills the entire space.

304
00:20:36,050 --> 00:20:38,460
But the width and height are most important.

305
00:20:38,460 --> 00:20:45,880
This ID field right here is not important within the actual layout

306
00:20:45,880 --> 00:20:49,060
unless we're using a relative layout and saying we can reference 

307
00:20:49,060 --> 00:20:52,990
one view position in reference to another.

308
00:20:52,990 --> 00:20:56,170
If we had a relative layout we could say position this below this one 

309
00:20:56,170 --> 00:20:59,390
or above this ID, but this ID will be important

310
00:20:59,390 --> 00:21:01,660
when we're using it in our code because we can reference 

311
00:21:01,660 --> 00:21:05,610
these individual views in this way.

312
00:21:05,610 --> 00:21:10,350
>> And then you can see the tag requestFocus, which is something you probably saw in pset 7.

313
00:21:10,350 --> 00:21:15,370
There was an auto focus tag or something along those lines for one of the fields.

314
00:21:15,370 --> 00:21:22,100
And one thing, of course, we can do just like in HTML,

315
00:21:22,100 --> 00:21:25,660
and notice one of the nice things about ADT is that it autocompletes here.

316
00:21:25,660 --> 00:21:29,930
Maybe not as nicely as it did in XCode, but it does nonetheless,

317
00:21:29,930 --> 00:21:32,860
and we could say hint and then give it some sort of string

318
00:21:32,860 --> 00:21:37,070
like write a message,

319
00:21:37,070 --> 00:21:41,300
and if I give it a moment, also notice that I get a little error here

320
00:21:41,300 --> 00:21:44,610
saying that we should use a string resource for this,

321
00:21:44,610 --> 00:21:48,820
so if I let it do some of the hard work for me

322
00:21:48,820 --> 00:21:57,320
I can select this string, do refractor Android and extract Android string.

323
00:21:57,320 --> 00:22:00,570
I can give it that name, write a message,

324
00:22:00,570 --> 00:22:04,180
and what it did now is it replaced that hard-coded string

325
00:22:04,180 --> 00:22:07,980
with a reference to the string in the string's .xml file,

326
00:22:07,980 --> 00:22:10,200
which means now this is here.

327
00:22:10,200 --> 00:22:15,560
>> And I know that seems a little trivial and like extra work at this point,

328
00:22:15,560 --> 00:22:17,840
but when you have a whole bunch of things, a whole bunch of strings,

329
00:22:17,840 --> 00:22:20,750
that's really important, and particularly for localization

330
00:22:20,750 --> 00:22:26,920
because as I mentioned earlier, Android is a very globally used operating system

331
00:22:26,920 --> 00:22:35,950
that you can simply do values-en or values-sp 

332
00:22:35,950 --> 00:22:44,320
or something for English or Spanish or other languages.

333
00:22:44,320 --> 00:22:50,210
And then you probably haven't had this experience yet

334
00:22:50,210 --> 00:22:53,030
since we didn't do much JavaScript in terms of web programming,

335
00:22:53,030 --> 00:22:56,850
but we can also do this field called onClick for the button,

336
00:22:56,850 --> 00:23:02,350
and this is a way of referencing within our layout

337
00:23:02,350 --> 00:23:06,570
that we want a certain function to be called in our source code.

338
00:23:06,570 --> 00:23:09,420
I'm going to call this sendMessage,

339
00:23:09,420 --> 00:23:13,390
and in order to make this work that means in the main activity here

340
00:23:13,390 --> 00:23:19,180
I will have to create a function that is public

341
00:23:19,180 --> 00:23:22,250
so that it can be accessed by the layout.

342
00:23:22,250 --> 00:23:25,930
It's void because you just don't want it to return anything.

343
00:23:25,930 --> 00:23:37,760
We'll call it sendMessage, and it takes a view,

344
00:23:37,760 --> 00:23:43,690
which is a sort of context that we can anchor this method

345
00:23:43,690 --> 00:23:47,160
to that individual view when we're running it.

346
00:23:47,160 --> 00:23:50,090
>> And I don't know if you noticed—well, you wouldn't have noticed,

347
00:23:50,090 --> 00:24:02,370
but at this point right here

348
00:24:02,370 --> 00:24:06,930
this view is a type that has not yet been included,

349
00:24:06,930 --> 00:24:10,630
and of course, you all know from CS50 about not including types.

350
00:24:10,630 --> 00:24:13,120
The nice thing about IDE's like Eclipse is that 

351
00:24:13,120 --> 00:24:17,520
if you forget to include a type it will underline with a little red squiggly

352
00:24:17,520 --> 00:24:19,680
and then give you the option to import the view.

353
00:24:19,680 --> 00:24:23,130
A quick way of doing that is control shift O, and it will import

354
00:24:23,130 --> 00:24:27,070
all the files that it needs to.

355
00:24:27,070 --> 00:24:33,670
Now that we have this function sendMessage,

356
00:24:33,670 --> 00:24:46,560
which is going to send message from the MainActivity to a new activity,

357
00:24:46,560 --> 00:24:55,230
we're going to have to use an intent to launch the new activity from this one,

358
00:24:55,230 --> 00:25:02,240
so we'll probably want to create a global constant or also particularly a public constant

359
00:25:02,240 --> 00:25:06,240
that will help us know how we're going to reference the string

360
00:25:06,240 --> 00:25:09,090
because when we create an intent we're not just calling a new activity,

361
00:25:09,090 --> 00:25:11,520
but we can also give it a bundle of information.

362
00:25:11,520 --> 00:25:14,720
A bundle is actually the term that Android uses,

363
00:25:14,720 --> 00:25:21,470
and it's a way of saying give it extra data, which it can't be of a very sophisticated data type,

364
00:25:21,470 --> 00:25:24,510
but we can definitely include booleans or strings or ints.

365
00:25:24,510 --> 00:25:29,750
That sort of thing.

366
00:25:29,750 --> 00:25:34,230
>> Feel free to ask about any of these qualifiers here,

367
00:25:34,230 --> 00:25:36,900
public, final, static.

368
00:25:36,900 --> 00:25:38,610
Public is the important one.

369
00:25:38,610 --> 00:25:47,090
It means that we can access this variable from other source code files

370
00:25:47,090 --> 00:25:49,590
such as when we create a new activity.

371
00:25:49,590 --> 00:25:52,190
We can reference the string within this file.

372
00:25:52,190 --> 00:25:57,160
If it's private, it means it's limited to this individual file here.

373
00:25:57,160 --> 00:26:02,430
But we'll call this something like extra message.

374
00:26:16,260 --> 00:26:23,300
Now we have made this function, and if we click the button, this function will be called.

375
00:26:23,300 --> 00:26:27,970
But we haven't done anything, obviously, with the function.

376
00:26:27,970 --> 00:26:33,130
What we want to do now is create a new activity,

377
00:26:33,130 --> 00:26:35,350
the activity that will actually be launched.

378
00:26:35,350 --> 00:26:44,330
In Eclipse we can say new, Android activity, blank activity.

379
00:26:44,330 --> 00:26:46,530
We can give it a name. 

380
00:26:46,530 --> 00:26:57,050
Let's call it our result activity.

381
00:26:57,050 --> 00:27:04,430
And then this hierarchical parent field is a way of specifying

382
00:27:04,430 --> 00:27:08,180
how the activities are related to each other.

383
00:27:08,180 --> 00:27:11,020
Because this one will be launched from the other activity

384
00:27:11,020 --> 00:27:27,520
we should specify that it has the parent main activity.

385
00:27:27,520 --> 00:27:31,220
>> And I could have clicked on the next field there, which would have told us

386
00:27:31,220 --> 00:27:33,830
some optional fields that it was also including,

387
00:27:33,830 --> 00:27:38,800
but the nice thing about ADT, again, is that if I scroll down here

388
00:27:38,800 --> 00:27:45,740
in the Manifest remember that all of this really was included by default

389
00:27:45,740 --> 00:27:48,930
when we originally created the project,

390
00:27:48,930 --> 00:27:53,090
and now because we used this create a new activity rather than just

391
00:27:53,090 --> 00:27:58,610
adding our own class file because we went through their GUI for doing this

392
00:27:58,610 --> 00:28:01,930
it already added all of this to the Manifest for us, 

393
00:28:01,930 --> 00:28:06,020
which just means that now the operating system won't complain

394
00:28:06,020 --> 00:28:09,400
when we try to launch this activity.

395
00:28:09,400 --> 00:28:14,620
And it also, of course, gave it a label, which also shows up in strings.

396
00:28:14,620 --> 00:28:17,340
It does a lot of things on the back end for us.

397
00:28:17,340 --> 00:28:20,140
Anyway, now that we have this result activity as well,

398
00:28:20,140 --> 00:28:23,810
the actual source code file in the source folder,

399
00:28:23,810 --> 00:28:33,540
and you can see—to briefly touch on this—

400
00:28:33,540 --> 00:28:37,790
because we told it about this hierarchical parent

401
00:28:37,790 --> 00:28:46,640
it gave this field android.r.ide.home in this onOption selected thing.

402
00:28:46,640 --> 00:28:49,020
>> What this is basically saying is there's a menu button now 

403
00:28:49,020 --> 00:28:53,110
that in the top left corner of the screen

404
00:28:53,110 --> 00:29:02,220
if I go back to the PowerPoint where we first talked about action bar

405
00:29:02,220 --> 00:29:05,380
because of the hierarchical parent now there's a little arrow back here

406
00:29:05,380 --> 00:29:10,610
and this is clickable so we should be able to—after we actually run this app—

407
00:29:10,610 --> 00:29:15,360
go back, and it's a way of saving us a little bit of code there.

408
00:29:26,220 --> 00:29:40,180
Now within this—well, it seems to be complaining about that for a moment.

409
00:29:40,180 --> 00:29:43,910
Let's comment that out.

410
00:29:43,910 --> 00:29:48,260
Now, in order to actually interact with these 2 activities,

411
00:29:48,260 --> 00:29:55,020
we have to create an intent which includes all of this data.

412
00:29:55,020 --> 00:29:58,950
In sendMessage now I'm going to cruise through some bits of code

413
00:29:58,950 --> 00:30:00,700
and explain that as I go.

414
00:30:00,700 --> 00:30:06,280
An intent, as I said, is a way to launch one activity from another.

415
00:30:06,280 --> 00:30:10,000
Intent is the type. We're creating a variable myIntent.

416
00:30:10,000 --> 00:30:13,980
>> And this is actually an object, which is why we have to call new.

417
00:30:13,980 --> 00:30:18,500
It's common Java usage there, which might take a little bit of getting used to.

418
00:30:18,500 --> 00:30:23,900
This means we're using the activity or the class MainActivity,

419
00:30:23,900 --> 00:30:28,630
and intent in that way takes the activity it's going from

420
00:30:28,630 --> 00:30:36,060
and the activity it's going to, which we call ResultActivity,

421
00:30:36,060 --> 00:30:38,170
and that is its own class.

422
00:30:38,170 --> 00:30:41,720
Include that.

423
00:30:41,720 --> 00:30:47,370
And then as I mentioned before, we gave that ID to the edit text field

424
00:30:47,370 --> 00:30:53,710
and the text view, so in order to programmatically capture

425
00:30:53,710 --> 00:31:01,860
the text that exists in the editText

426
00:31:01,860 --> 00:31:06,710
we use this function called findViewByID,

427
00:31:06,710 --> 00:31:13,660
which is similar to something that you'll use when trying to get fields from the DOM.

428
00:31:13,660 --> 00:31:17,560
Perhaps David talks about this in lecture.

429
00:31:17,560 --> 00:31:26,600
But it's just a way of getting those—that's why we tag these things with those fields.

430
00:31:26,600 --> 00:31:31,110
Id.editText1.

431
00:31:31,110 --> 00:31:35,220
It's already autocompleting for me there.

432
00:31:35,220 --> 00:31:42,010
>> And then we'll also include—this editText now that we have the field

433
00:31:42,010 --> 00:31:47,640
within our program, all that findViewByID did was basically

434
00:31:47,640 --> 00:31:50,870
you could think of it as give us a reference to that editText.

435
00:31:50,870 --> 00:31:54,570
Now we want to get the string or the message

436
00:31:54,570 --> 00:32:00,670
within that editText which we can do by using the—

437
00:32:00,670 --> 00:32:03,360
you could think of editText as a struct—

438
00:32:03,360 --> 00:32:07,600
we call it an object in Java—with a whole bunch of different methods

439
00:32:07,600 --> 00:32:10,650
or fields and attributes attached to it.

440
00:32:10,650 --> 00:32:15,510
When I say editText. it gives me the chance to access

441
00:32:15,510 --> 00:32:19,770
a method such as getText, which will get the current text

442
00:32:19,770 --> 00:32:23,990
in that editText and then convert that explicitly 

443
00:32:23,990 --> 00:32:26,520
to a string, and we have saved the message.

444
00:32:26,520 --> 00:32:32,730
Now we actually want to do something with that intent we created just moments ago.

445
00:32:32,730 --> 00:32:40,250
I will put extra as it's called in the intent,

446
00:32:40,250 --> 00:32:43,330
which, again, like I said before, this is a way of creating the bundle

447
00:32:43,330 --> 00:32:45,980
with a whole bunch of data.

448
00:32:45,980 --> 00:32:50,920
Extra message is our tag so we know what we're saving this under,

449
00:32:50,920 --> 00:32:56,700
and then I'm including the message.

450
00:32:56,700 --> 00:33:04,870
>> And then we can actually start the activity by giving it the parameter myIntent.

451
00:33:04,870 --> 00:33:10,630
And this will actually launch the activity, so now since I upgraded to Windows 8

452
00:33:10,630 --> 00:33:15,870
there might be some errors that show up briefly, but try to ignore them.

453
00:33:28,010 --> 00:33:30,310
And this is the Android emulator.

454
00:33:30,310 --> 00:33:33,540
Hopefully the code will actually pop up in a moment.

455
00:33:33,540 --> 00:33:36,680
Again, ignoring all those little things.

456
00:33:36,680 --> 00:33:42,290
But the Android emulator you can emulate any version of the operating system

457
00:33:42,290 --> 00:33:45,180
from the earliest ones, Donut, Gingerbread.

458
00:33:45,180 --> 00:33:49,640
This is Jelly Bean 4.1.

459
00:33:49,640 --> 00:33:53,150
But as you can see right now, this is something we made.

460
00:33:53,150 --> 00:33:55,780
This has the MainActivity, the editText, the button.

461
00:33:55,780 --> 00:34:01,550
I can type something here, but what are we missing at this point?

462
00:34:01,550 --> 00:34:05,190
We made the field in the MainActivity that's going to send the message

463
00:34:05,190 --> 00:34:08,570
to the other activity, but at this point

464
00:34:08,570 --> 00:34:12,330
we haven't done anything in the other activity, so it's not going to receive anything.

465
00:34:12,330 --> 00:34:18,800
Let's finish up that part before we move on.

466
00:34:18,800 --> 00:34:25,760
>> This result activity, what we'll need to do is we'll need to do is we'll need to—

467
00:34:25,760 --> 00:34:30,070
we can also reference the intent within this activity,

468
00:34:30,070 --> 00:34:33,580
so we have to capture the intent, which is really simple.

469
00:34:33,580 --> 00:34:40,780
It's a function included in the activity class,

470
00:34:40,780 --> 00:34:47,610
so we can just say "Get the message from the intent."

471
00:34:47,610 --> 00:34:56,260
"Intent myIntent = getIntent."

472
00:34:56,260 --> 00:35:00,030
And this will give us—now myIntent is an object,

473
00:35:00,030 --> 00:35:05,380
which is a reference to the intent that led us to this activity.

474
00:35:05,380 --> 00:35:10,130
MainActivity calls and gives extra information to result activity.

475
00:35:10,130 --> 00:35:14,070
Result activity now looks at the intent that led it here,

476
00:35:14,070 --> 00:35:23,540
and we can access the message that we created in the other one,

477
00:35:23,540 --> 00:35:26,370
getStringExtra, and this will autocomplete for me.

478
00:35:26,370 --> 00:35:31,190
And then remember, the way we tagged that bit of data

479
00:35:31,190 --> 00:35:38,400
was by giving it this field right here, this public string,

480
00:35:38,400 --> 00:35:42,080
which is the tag for the string we actually included.

481
00:35:42,080 --> 00:35:48,450
>> If I say MainActivity.Extra_Message

482
00:35:48,450 --> 00:35:52,200
it's right there, and this is sort of like the parameter name

483
00:35:52,200 --> 00:35:55,330
when we passed code from the controller to the template,

484
00:35:55,330 --> 00:35:57,680
when we'd say title arrow something.

485
00:35:57,680 --> 00:36:01,140
It's the same sort of idea there.

486
00:36:01,140 --> 00:36:07,130
Now, remember this.

487
00:36:07,130 --> 00:36:12,230
We also had this auto created or auto generated code

488
00:36:12,230 --> 00:36:16,410
for result activity, which includes the text view in the middle

489
00:36:16,410 --> 00:36:19,690
that says hello world.

490
00:36:19,690 --> 00:36:27,510
We could potentially make that bigger.

491
00:36:27,510 --> 00:36:33,980
Let's do that first.

492
00:36:33,980 --> 00:36:39,550
We could make it 40 density independent pixels. 

493
00:36:39,550 --> 00:36:42,670
Let's see, that's super huge. That will be okay.

494
00:36:42,670 --> 00:36:48,180
And then in order to reference this individual text view within our code

495
00:36:48,180 --> 00:36:53,890
we'll need to give it an ID,

496
00:36:53,890 --> 00:36:58,350
and in order to do that we say @+id, which means we assign it ID.

497
00:36:58,350 --> 00:37:02,480
If we just said @id it would assume we're referencing an ID that already exists,

498
00:37:02,480 --> 00:37:07,760
and let's call this our resultTextView.

499
00:37:07,760 --> 00:37:10,570
And notice that in XML there's no need for semicolons or anything.

500
00:37:10,570 --> 00:37:12,380
Everything is within these tags.

501
00:37:12,380 --> 00:37:15,530
It's very similar to HTML in a lot of senses.

502
00:37:15,530 --> 00:37:22,760
>> It takes a little bit of getting used to, but eventually you'll feel pretty comfortable with it.

503
00:37:22,760 --> 00:37:31,320
Let's update the text for our result text view,

504
00:37:31,320 --> 00:37:35,650
and as we did when we were getting that edit text field in our other activity

505
00:37:35,650 --> 00:37:46,630
in MainActivity here we will also likewise—

506
00:37:46,630 --> 00:37:54,890
we'll find the view by the ID.

507
00:37:54,890 --> 00:37:59,640
And R, in case I didn't mention this before, is the reference to our resources folder,

508
00:37:59,640 --> 00:38:05,350
and then ID is a reference to everything in the resources folder, all the IDs,

509
00:38:05,350 --> 00:38:10,060
and resultTextView.

510
00:38:10,060 --> 00:38:13,010
And just as before, resultTextView is an object,

511
00:38:13,010 --> 00:38:15,780
which means it has all these properties associated with it.

512
00:38:15,780 --> 00:38:20,610
When we use getText for the edit text for this text field or the text view

513
00:38:20,610 --> 00:38:23,980
we can actually use setText,

514
00:38:23,980 --> 00:38:26,960
and then we already found the message from the intent,

515
00:38:26,960 --> 00:38:35,760
so I can say message, and this will actually set the message.

516
00:38:35,760 --> 00:38:41,820
>> It take a moment to launch, and then we can see whether or not it crashes,

517
00:38:41,820 --> 00:38:48,670
but any questions about that process right there, that sort of interaction?

518
00:38:48,670 --> 00:38:51,490
In many ways it's straightforward.

519
00:38:51,490 --> 00:38:53,960
The reason I'm going through something relatively simple

520
00:38:53,960 --> 00:38:57,330
is, again, because you get to see the interaction between the layout,

521
00:38:57,330 --> 00:38:59,520
the source code, how you reference things

522
00:38:59,520 --> 00:39:07,680
and maybe get a little exposure to how Java works there.

523
00:39:07,680 --> 00:39:16,500
If I actually type something in here, like ohai, and then I click the button,

524
00:39:16,500 --> 00:39:22,260
it launches a new activity, and that text view says ohai.

525
00:39:22,260 --> 00:39:27,640
That's very simple, but hopefully after that example

526
00:39:27,640 --> 00:39:32,310
you sort of see how this interaction works, and now that mess of files

527
00:39:32,310 --> 00:39:36,870
on the left side for all these project folders, hopefully you know where to look now.

528
00:39:36,870 --> 00:39:38,700
This is your source code area.

529
00:39:38,700 --> 00:39:41,760
>> Layout is really the only thing you'll deal with until you include images

530
00:39:41,760 --> 00:39:46,370
and the drawables or whatever, and values, that will include strings,

531
00:39:46,370 --> 00:39:51,960
as we mentioned, and then styles is something that's sort of like CSS.

532
00:39:51,960 --> 00:39:56,410
Address it when you want, but until you feel comfortable with adding extra flair

533
00:39:56,410 --> 00:40:02,520
to your application there's no need to worry about it too much.

534
00:40:02,520 --> 00:40:07,410
Just to wrap up one other thing you will definitely want to include—

535
00:40:07,410 --> 00:40:13,010
assuming you want to integrate cool features and save yourself some extra coding—

536
00:40:13,010 --> 00:40:16,460
would be to include 3rd party libraries.

537
00:40:16,460 --> 00:40:19,840
Here's the little Android guy with the Sherlock Holmes hat.

538
00:40:19,840 --> 00:40:23,040
This is an action bar Sherlock library, 

539
00:40:23,040 --> 00:40:25,390
which basically means that action bar you saw earlier, 

540
00:40:25,390 --> 00:40:29,590
which is now standard in Ice Cream Sandwich and Jelly Bean,

541
00:40:29,590 --> 00:40:33,100
if you want to bring that sort of user experience to users on older versions

542
00:40:33,100 --> 00:40:39,290
and save yourself from worrying about how the user is going to navigate

543
00:40:39,290 --> 00:40:42,490
on older versions when that thing isn't there you can include this library

544
00:40:42,490 --> 00:40:46,770
and then you just have to reference—rather than the default Android

545
00:40:46,770 --> 00:40:50,250
libraries for the action bar, you reference this support library.

546
00:40:50,250 --> 00:40:53,090
>> Things like Scoreloop, it's great if you're going to include a game.

547
00:40:53,090 --> 00:40:57,280
It lets you add leader boards and achievements to games.

548
00:40:57,280 --> 00:41:00,900
Admob is a way of putting ads into your applications

549
00:41:00,900 --> 00:41:02,900
in case you want to make a little bit of money off of it.

550
00:41:02,900 --> 00:41:05,730
Of course, there is Facebook and Twitter for integrating there 

551
00:41:05,730 --> 00:41:08,170
if you want to share things easily, et cetera.

552
00:41:08,170 --> 00:41:15,120
Dropbox, likewise, and Google Analytics is that chart looking one there.

553
00:41:15,120 --> 00:41:19,070
That will be very important if you actually want to see who is interacting 

554
00:41:19,070 --> 00:41:25,800
with your app or who it is, how they interact, et cetera.

555
00:41:25,800 --> 00:41:30,650
Google, by default, tells you a lot of statistics about who has installed your app

556
00:41:30,650 --> 00:41:35,020
and what phones they have, what operating system versions they have.

557
00:41:35,020 --> 00:41:38,080
But if you want to see who is using it on a daily basis and how they use it

558
00:41:38,080 --> 00:41:42,860
then you'll want to include some sort of tracking system like that.

559
00:41:42,860 --> 00:41:44,990
>> When you're ready to distribute your app

560
00:41:44,990 --> 00:41:46,930
I don't need to go into that in too much depth.

561
00:41:46,930 --> 00:41:49,090
Click on the link here, Google Play.

562
00:41:49,090 --> 00:41:51,080
It used to be the Android market.

563
00:41:51,080 --> 00:41:53,470
They rebranded everything with Google Play,

564
00:41:53,470 --> 00:41:55,230
so now you submit to that.

565
00:41:55,230 --> 00:41:57,140
It's very straightforward.

566
00:41:57,140 --> 00:42:01,070
You have to include a description, some screenshots.

567
00:42:01,070 --> 00:42:05,660
Like I said, there's no approval process like iOS.

568
00:42:05,660 --> 00:42:07,270
And where to go from here?

569
00:42:07,270 --> 00:42:09,450
I showed you a really simple example.

570
00:42:09,450 --> 00:42:13,270
Hopefully if it seems terribly simple

571
00:42:13,270 --> 00:42:15,740
then that's probably a good sign.

572
00:42:15,740 --> 00:42:20,080
If you at all felt a little bit confused or unsure about exactly what I was typing

573
00:42:20,080 --> 00:42:26,160
that's also fine, but from here go to Google Guides.

574
00:42:26,160 --> 00:42:28,330
This is a great place to start.

575
00:42:28,330 --> 00:42:31,460
It will talk you through what they expect in terms of the application design,

576
00:42:31,460 --> 00:42:33,380
how the users normally interact with it.

577
00:42:33,380 --> 00:42:36,450
It's much more free form than iOS, I'd say,

578
00:42:36,450 --> 00:42:41,330
which it seems like table views are—I don't know, that's their bread and butter.

579
00:42:41,330 --> 00:42:44,690
Everything is a table view sliding up and down.

580
00:42:44,690 --> 00:42:48,160
With Android they definitely encourage people to look at it from  

581
00:42:48,160 --> 00:42:51,720
a whole bunch of different perspectives.

582
00:42:51,720 --> 00:42:56,000
>> When you include the software development kit in this ADT

583
00:42:56,000 --> 00:43:03,010
by default you have a whole bunch of sample projects in Android.

584
00:43:03,010 --> 00:43:05,470
Right here, Android, Android Sample Project.

585
00:43:05,470 --> 00:43:11,870
If I click on that, then I can choose a version for which of the sample projects apply.

586
00:43:11,870 --> 00:43:13,300
There's a whole bunch of different things here.

587
00:43:13,300 --> 00:43:16,690
It starts off with action bar compatibility,

588
00:43:16,690 --> 00:43:24,610
accelerometer play, backup and restore, Bluetooth, gesture builder.

589
00:43:24,610 --> 00:43:28,930
JetBoy is a sample game they give you, as is LunarLander.

590
00:43:28,930 --> 00:43:31,250
There are a whole bunch of sample applications here,

591
00:43:31,250 --> 00:43:35,290
and they're all targeted at different aspects of Android's API,

592
00:43:35,290 --> 00:43:41,520
and the idea is that as you make your application

593
00:43:41,520 --> 00:43:44,110
you don't need to learn everything about Android to make an Android app.

594
00:43:44,110 --> 00:43:47,300
You only have to learn about the parts that you're actually going to use.

595
00:43:47,300 --> 00:43:49,340
Look at these sample libraries. 

596
00:43:49,340 --> 00:43:51,510
Feel free to copy and paste the code and reapply it.

597
00:43:51,510 --> 00:43:53,850
It's a great thing to look at more difficult code

598
00:43:53,850 --> 00:43:57,060
and try to understand it, which is of course why in CS50 

599
00:43:57,060 --> 00:44:01,510
we often give you large amounts of source code.

600
00:44:01,510 --> 00:44:04,620
Look at some of these if you're going to use similar libraries

601
00:44:04,620 --> 00:44:08,630
and then apply it to your own code.

602
00:44:08,630 --> 00:44:10,430
And of course, there are tutorials.

603
00:44:10,430 --> 00:44:12,690
Search for tutorials.

604
00:44:12,690 --> 00:44:17,020
I found a lot of good ones online which can bring you up to speed

605
00:44:17,020 --> 00:44:20,080
with what fragments really are and how you can use them.

606
00:44:20,080 --> 00:44:22,240
>> Some of these new design things, like fragments,

607
00:44:22,240 --> 00:44:26,840
you really don't have to be worried about unless you're making a 

608
00:44:26,840 --> 00:44:30,560
pretty large in scope project.

609
00:44:30,560 --> 00:44:32,510
They are things that Google is trying to phase in.

610
00:44:32,510 --> 00:44:35,570
Stackoverflow is of course your friend.

611
00:44:35,570 --> 00:44:37,930
Hopefully I sold you a bit on Android, 

612
00:44:37,930 --> 00:44:41,640
realizing it's much more easy to approach in terms of just the coding language.

613
00:44:41,640 --> 00:44:45,970
Java is I'd say much easier to understand than Objective-C.

614
00:44:45,970 --> 00:44:50,780
Android is growing I think much more than iOS.

615
00:44:50,780 --> 00:44:54,890
I mean, the data is there too, aside from what I think.

616
00:44:54,890 --> 00:44:56,920
It's going to be around for a while,

617
00:44:56,920 --> 00:45:00,880
and they are a few years behind in terms of their design cycles,

618
00:45:00,880 --> 00:45:04,690
so it's sort of understandable that they're still working through some of these 

619
00:45:04,690 --> 00:45:09,080
consistency questions, like this action bar is a new thing for them still,

620
00:45:09,080 --> 00:45:16,010
sort of creating similar user experience across all their apps.

621
00:45:16,010 --> 00:45:20,650
Hopefully you can go forward now and open up Eclipse 

622
00:45:20,650 --> 00:45:22,870
and make your own Android apps.

623
00:45:22,870 --> 00:45:30,240
>> Does anyone have any questions before we wrap up about anything?

624
00:45:30,240 --> 00:45:34,410
I can tell you the answer is 42.

625
00:45:34,410 --> 00:45:41,990
Well, happy coding everyone, and good luck.

626
00:45:41,990 --> 00:45:44,990
[CS50.TV]