Creating an Android app Lesson 4 Running Your App

If you followed the previous lesson to create an Android project, it includes a default set of "Hello World" source files that allow you to immediately run the app.

How you run your app depends on two things: whether you have a real Android-powered device and whether you're using Eclipse. This lesson shows you how to install and run your app on a real device and on the Android emulator, and in both cases with either Eclipse or the command line tools.

Before you run your app, you should be aware of a few directories and files in the Android project:

AndroidManifest.xml

                The manifest file describes the fundamental characteristics of the app and defines each of its components. You'll learn about various declarations in this file as you read more training classes.

One of the most important elements your manifest should include is the <uses-sdk> element. This declares your app's compatibility with different Android versions using the android:minSdkVersion and android:targetSdkVersion attributes. For your first app, it should look like this:

                <manifest xmlns:android="http://schemas.android.com/apk/res/android" ... >

  <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="17" />

    ...

</manifest>

You should always set the android:targetSdkVersion as high as possible and test your app on the corresponding platform version. For more information, read Supporting Different Platform Versions.

src/

Directory for your app's main source files. By default, it includes an Activity class that runs when your app is launched using the app icon.

res/

Contains several sub-directories for app resources. Here are just a few:

drawable-hdpi/

Directory for drawable objects (such as bitmaps) that are designed for high-density (hdpi) screens. Other drawable directories contain assets designed for other screen densities.

layout/

Directory for files that define your app's user interface.

values/

Directory for other various XML files that contain a collection of resources, such as string and color definitions.

When you build and run the default Android app, the default Activity class starts and loads a layout file that says "Hello World." The result is nothing exciting, but it's important that you understand how to run your app before you start developing.