Familiarizing Yourself with Eclipse
Let’s begin by writing a simple Android “Hello, World” application that displays a line of text to the user. As you do so, you will also be taking a tour through the Eclipse environment. Specifically, you will learn about some of the features offered by the Android Development Tools (ADT) plug-in for Eclipse. The ADT plug-in provides functionality for developing, compiling, packaging, and deploying Android applications. Specifically, the ADT plug-in provides the following features:
- The Android Project Wizard, which generates all the required project files
- Android-specific resource editors, including a Graphical Layout editor for designing Android application user interfaces
- The Android SDK Manager
- The Android Virtual Devices (AVD) Manager
- The Eclipse DDMS perspective for monitoring and debugging Android applications
- Integration with the Android LogCat logging utility
- Integration with the Android Hierarchy Viewer layout utility
- Automated builds and application deployment to Android emulators and devices
- Application packaging and code signing tools for release deployment, including ProGuard support for code optimization and obfuscation
Now, let’s take some of these features for a spin.
Creating Android Projects
The Android Project Wizard creates all the required files for an Android application. Open Eclipse and follow these steps to create a new project:
- Choose File, New, Android Project, or click the Android Project creator icon ) on the Eclipse toolbar.
- Choose a project name. In this case, name the project HelloKindle. The first time you try to create an Android Project in Eclipse, you might need to choose File, New, Project..., and then select the Android, Android Project. After you do this once, it appears in the Eclipse project types, and you can use the method described in Step 1.
- Choose a location for the project source code. Because this is a new project, select the Create New Project in Workspace radio button. If you prefer to store your project files in a location other than the default, simply uncheck the Use Default Location check box and browse to the directory of your choice. The settings should look like Figure 1.2.
Figure 1.2. Project Name and Location
- Press the Next button.
- Select a build target for your application, as shown in Figure 1.3. For most applications, you want to select the version of Android most appropriate for the devices used by your target audience and the needs of your application. For Kindle development, choose API Level 10 (Android 2.3.3) using the Android Open Source Project vender version (not the Google, Inc., vender version). Kindle Fire devices do not have access to Google add-ons.
Figure 1.3. Choose SDK Target
- Press the Next button.
- Specify an application name. This name is what users will see. In this case, call the application Hello Kindle.
- Specify a package name, following standard package namespace conventions for Java. Because all the code in this book falls under the com.kindlebook.* namespace, use the package name com.kindlebook.hellokindle.
- Check the Create Activity check box. This instructs the wizard to create a default launch Activity class for the application. Call your activity HelloKindleActivity.
- Confirm that the Minimum SDK field is correct. This field will be set to the API level of the build target by default. (Android 2.3.3 is API Level 10.) If you want to support older versions of the Android SDK, you need to change this value. For example, to support devices with Android 1.6, set the Min SDK Version to API Level 4. The Kindle is based on API Level 10, however, so an application just targeting the Kindle does not need to worry about this. Your project settings will look like what’s shown in Figure 1.4.
Figure 1.4. Configure Package Name, Initial Activity, and Minimum SDK
- The Android Project Wizard allows you to create a test project in conjunction with your Android application, also shown in Figure 1.4. For this example, a test project is unnecessary. However, you can always add a test project later by clicking the Android Test Project creator icon, which is to the right of the Android Project Wizard icon ) on the Eclipse toolbar.
- Click the Finish button.
Exploring the Android Project Files
You will now see a new Android project called HelloKindle in the Eclipse File Explorer. In addition to linking the appropriate Android SDK jar file, the following core files and directories are created:
- AndroidManifest.xml—The central configuration file for the application.
- project.properties—A generated build file used by Eclipse and the Android ADT plug-in. Do not edit this file.
- proguard.cfg—A generated build file used by Eclipse, ProGuard, and the Android ADT plug-in. Edit this file to configure your code optimization and obfuscation settings for release builds.
- /src folder—Required folder for all source code.
- /src/com.kindlebook.hellokindle/HelloKindleActivity.java—Main entry point to this application, named HelloKindleActivity. This activity has been defined as the default launch activity in the Android manifest file.
- /gen/com.kindlebook.hellokindle/R.java—A generated resource management source file. Do not edit this file.
- /assets folder—Required folder where uncompiled file resources can be included in the project.
- /res folder—Required folder where all application resources are managed. Application resources include animations, drawable graphics, layout files, data-like strings and numbers, and raw files.
- /res/drawable-* folders—Application icon graphic resources are included in several sizes for different device screen resolutions.
- /res/layout/main.xml—Layout resource file used by DroidActivity to organize controls on the main application screen.
- /res/values/strings.xml—The resource file where string resources are defined.
Editing Project Resources
The Android manifest file is the central configuration file for an Android application. Double-click the AndroidManifest.xml file within your new project to launch the Android manifest file editor (see Figure 1.5).
Figure 1.5. Editing the Android Manifest File in Eclipse
Editing the Android Manifest File
The Android manifest file editor organizes the manifest information into a number of tabs:
- Manifest—This tab, shown in Figure 1.5, is used for general application-wide settings, such as the package name and application version information (used for installation and upgrade purposes).
- Application—This tab is defines application details, such as the name and icon the application displays, as well as the “guts” of the application, such as what activities can be run (including the default launch DroidActivity) and other functionality and services that the application provides.
- Permissions—This tab defines the application’s permissions. For example, if the application requires the ability to access Internet resources, it must register a uses-permission tag within the manifest, with the name android.permission.INTERNET.
- Instrumentation—This tab is used for unit testing, using the various instrumentation classes available within the Android SDK.
- AndroidManifest.xml—This tab provides a simple XML editor to directly edit the manifest file. Because all Android resource files, including the Android manifest file, are simply XML files, you can always edit the XML instead of using the resource editors. You can create a new Android XML resource file by clicking the Android XML creator icon () on the Eclipse toolbar.
If you switch to the AndroidManifest.xml tab, your manifest file will look something like this:
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.kindlebook.hellokindle" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="10" android:targetSdkVersion="10" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".HelloKindleActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
Editing Other Resource Files
Android applications are made up of functions (Java code, classes) and data (including resources like graphics, strings, and so on). Most Android application resources are stored under the /res subdirectory of the project. The following subdirectories are also available by default in a new Android project:
- /drawable-ldpi, /drawable-hdpi, /drawable-mdpi—These subdirectories store graphics and drawable resource files for different screen densities and resolutions. If you browse through these directories using the Eclipse Project Explorer, you will find the icon.png graphics file in each one; this is your application’s icon.
- /layout—This subdirectory stores user interface layout files. Within this subdirectory, you will find the main.xml screen layout resource file that defines the user interface for the one activity in this simple application.
- /values—This subdirectory organizes the various types of resources, such as text strings, color values, and other primitive types. Here, you find the strings.xml resource file, which contains all the string resources used by the application.
If you double-click any of resource files, the resource editor will launch. Remember that you can always directly edit the XML. For example, let’s try editing a string resource file. If you inspect the main.xml layout file of the project, you notice that it displays a simple layout with a single TextView control. This user interface control simply displays a string. In this case, the string displayed is defined in the string resource called @string/hello. To edit the string resource called @string/hello, using the string resource editor, follow these steps:
- Open the strings.xml file in the resource editor by double-clicking it in the Eclipse Package Explorer.
- Select the String called hello and note the name (hello) and value (Hello World, HelloKindleActivity!) shown in the resource editor.
- Within the Value field, change the text to Hello, Kindle Fire.
- Save the file.
If you switch to the strings.xml tab and look through the raw XML, you notice that two string elements are defined within a <resources> block:
<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello, Kindle Fire</string> <string name="app_name">Hello Kindle</string> </resources>
The first resource is the string called @string/hello. The second resource is the string called @string/app_name, which contains the name label for the application. If you look at the Android manifest file again, you see @string/app_name used in the application configuration.
We talk more about project resources in Chapter 4, “Managing Application Resources.” For now, let’s move on to compiling and running the application.