Writing Your First Android Application
You should now have a workable Android development environment set up on your computer. Ideally, you have an Android device as well. Now it’s time for you to start writing some Android code. In this chapter, you learn how to install the Android sample applications and to add and create Android projects from within the Android IDE. You also learn how to verify that your Android development environment is set up correctly. You then write and debug your first Android application in the software emulator and on an Android device.
Testing Your Development Environment
The best way to make sure you configured your development environment correctly is to run an existing Android application. You can do this easily by using one of the sample applications provided as part of the Android SDK in the samples subdirectory found where your Android SDK is installed.
Within the Android SDK sample applications, you will find a classic game called Snake (http://en.wikipedia.org/wiki/Snake_(video_game)). To build and run the Snake application, you must create a new Android project in your Android IDE workspace based on the existing Android sample project, create an appropriate Android Virtual Device (AVD) profile, and configure a launch configuration for that project. After you have everything set up correctly, you can build the application and run it on the Android emulator and on an Android device. By testing your development environment with a sample application, you can rule out project configuration and coding issues and focus on determining whether the tools are set up properly for Android development. After this fact has been established, you can move on to writing and compiling your own applications.
Adding the Android Samples Using the SDK Manager
One quick way to learn how to develop Android applications is by reviewing an application that has already been created. There are many Android applications available for this purpose, but first we must download them. Here is how:
From within the Android IDE, click the Android SDK Manager icon () to open the Android SDK Manager. You should see a dialog similar to that in Figure 3.1.
Figure 3.1 The Android SDK Manager.
- You now need to install the Samples for SDK listed under Android 4.3 (API 18), so go ahead and select this item. You may also want to install a few additional items along with the samples, so select the following for installation (shown in Figure 3.1): Documentation for Android SDK and Google APIs. Then click Install Packages. Make sure that the proper SDK Tools, Platform-tools, Build-tools, SDK Platform, and System Image are installed as well; if they are not, you should select those for installation now, too.
A new dialog appears (see Figure 3.2) asking you to accept the license agreement for the packages that you will be installing. You may accept or reject each license individually by highlighting a particular package in the left pane and choosing Accept or Reject, or you can accept them all at once by highlighting Android SDK License in the left pane and choosing Accept License. Let’s accept all the licenses together by selecting Android SDK License in the left pane, choosing Accept License, and then clicking Install. This will initiate the installation of the selected packages. Wait until the installation is complete.
Figure 3.2 Accepting the license agreements.
Now that the installation is completed, you are ready to begin loading Android sample projects into your workspace.
Adding the Snake Project to Your Android IDE Workspace
To add the Snake project to your Android IDE workspace, follow these steps:
- Choose File, New, Other....
Choose Android, Android Sample Project (see Figure 3.3). Click Next.
Figure 3.3 Creating a new Android sample project.
Choose your build target (see Figure 3.4). In this case, we’ve picked Android 4.3, API Level 18, from the Android Open Source Project. Click Next.
Figure 3.4 Choose an API level for the sample.
Select which sample you want to create (see Figure 3.5). Choose Snake.
Figure 3.5 Picking the Snake sample project.
Click Finish. You now see the Snake project files in your workspace (see Figure 3.6).
Figure 3.6 The Snake project files.
Creating an AVD for Your Snake Project
The next step is to create an AVD that describes what type of device you want to emulate when running the Snake application. This AVD profile describes what type of device you want the emulator to simulate, including which Android platform to support. You do not need to create new AVDs for each application, only for each device you want to emulate. You can specify different screen sizes and orientations, and you can specify whether the emulator has an SD card and, if it does, what capacity the card has.
For the purposes of this example, an AVD for the default installation of Android 4.3 suffices. Here are the steps to create a basic AVD:
Launch the Android Virtual Device Manager from within the Android IDE by clicking the little Android device icon on the toolbar (). If you cannot find the icon, you can also launch the manager through the Window menu of the Android IDE. You should now see the Android Virtual Device Manager window (see Figure 3.7).
Figure 3.7 Android Virtual Device Manager.
- Click the New button.
- Choose a name for your AVD. Because we are going to take all the defaults, give this AVD a name of AndroidVanilla.
- Choose a device. This option controls the different resolutions of the emulator. We want to choose a typical device size, so in this case, select Nexus 4 (4.7”, 768 × 1280: xhdpi). This option most directly correlates to the popular Nexus 4 Google-branded device. Feel free to choose the most appropriate device to match the Android device on which you plan to run the application.
- Choose a build target. We want a typical Android 4.3 device, so choose Google APIs (Google Inc.) – API Level 18 from the drop-down menu. In addition to including the Android APIs, this option will also include the Google APIs and applications, such as the Maps application, as part of the platform image. Although we could choose the standard Android 4.3 – APIs Level 18 for this project, it is important to be aware of the additional options the Google APIs provide.
- For the Memory Options setting, you may have to try different values for optimal performance depending on the memory configuration of your development machine. The default RAM value for this virtual device is 1907 and the VM Heap is 64. If your machine is older and does not have a lot of memory, you may need to lower this value significantly to something like 512. The development machine used for this book has 8GB of RAM with a fairly powerful quad-core processor, and the RAM value we decided to use is 768 with the VM Heap set to 64.
- Choose an SD card capacity, in either kibibytes or mibibytes. (Not familiar with kibibytes? See this Wikipedia entry: http://en.wikipedia.org/wiki/Kibibyte.) This SD card image will take up space on your hard drive and may also take a long time to allocate, so choose something reasonable, such as 1024MiB.
Seriously consider enabling the Snapshot feature listed under Emulation Options. This greatly improves emulator startup performance. See Appendix B, “Quick-Start Guide: The Android Emulator,” for details.
Your project settings will look like Figure 3.8.
Figure 3.8 Creating a new AVD.
- Click the OK button to create the AVD, and then wait for the operation to complete.
You should now see the AVD that you just created listed within your Android Virtual Device Manager (see Figure 3.9).
Figure 3.9 The new AVD is now listed.
For more information on creating different types of AVDs, check out Appendix B.
Creating a Launch Configuration for Your Snake Project
Next, you must create a launch configuration in the Android IDE to configure under what circumstances the Snake application builds and launches. The launch configuration is where you configure the emulator options to use and the entry point for your application.
You can create Run configurations and Debug configurations separately, each with different options. These configurations are created under the Run menu in the Android IDE (Run, Run Configurations... and Run, Debug Configurations...). Follow these steps to create a basic Debug configuration for the Snake application:
- Choose Run, Debug Configurations....
- Double-click Android Application to create a new configuration.
- Name your Debug configuration SnakeDebugConfig.
Choose the project by clicking the Browse button and choosing the Snake project (see Figure 3.10).
Figure 3.10 Naming the Debug configuration in the Android IDE.
Switch to the Target tab and, from the preferred AVD list, choose the AndroidVanilla AVD created earlier, as shown in Figure 3.11.
Figure 3.11 Target AVD for the Debug configuration in the Android IDE.
- Choose Apply and then Close.
You can set other emulator and launch options on the Target and Common tabs, but for now we are leaving the defaults as they are.
Running the Snake Application in the Android Emulator
Now you can run the Snake application using the following steps:
- Choose the Debug As icon drop-down menu on the toolbar ().
- Pull the drop-down menu and choose the SnakeDebugConfig you created. If you do not see the SnakeDebugConfig listed, find it in the Debug Configurations... listing and click the Debug button. Subsequent launches can be initiated from the little bug drop-down.
The Android emulator starts up; this might take a few moments to initialize. Then the application will be installed or reinstalled onto the emulator.
Figure 3.12 Configuring AVD launch options.
If necessary, swipe the screen from left to right to unlock the emulator, as shown in Figure 3.13.
Figure 3.13 The Android emulator launching (locked).
The Snake application starts and you can play the game, as shown in Figure 3.14.
Figure 3.14 The Snake game in the Android emulator.
You can interact with the Snake application through the emulator and play the game. You can also launch the Snake application from the All Apps screen at any time by clicking its application icon. There is no need to shut down and restart the emulator every time you rebuild and reinstall your application for testing. Simply leave the emulator running on your computer in the background while you work in the Android IDE and then redeploy using the Debug configuration again.