Programming in Android

Welcome to Android application development!

This class teaches you how to build your first Android app. You’ll learn how to create an Android project and run a debuggable version of the app. You'll also learn some fundamentals of Android app design, including how to build a simple user interface and handle user input.

Before you start this class, be sure you have your development environment set up. You need to:

1.    Download the Android SDK.

2.    Install the ADT plugin for Eclipse (if you’ll use the Eclipse IDE).

3.    Download the latest SDK tools and platforms using the SDK Manager.

Create a Project with Command Line Tools

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If you're not using the Eclipse IDE with the ADT plugin, you can instead create your project using the SDK tools from a command line:

1.    Change directories into the Android SDK’s tools/ path.

2.    Execute:

android list targets

This prints a list of the available Android platforms that you’ve downloaded for your SDK. Find the platform against which you want to compile your app. Make a note of the target id. We recommend that you select the highest version possible. You can still build your app to support older versions, but setting the build target to the latest version allows you to optimize your app for the latest devices.

If you don't see any targets listed, you need to install some using the Android SDK Manager tool. See Adding Platforms and Packages.

3.    Execute:

4.  android create project --target <target-id> --name MyFirstApp \

5.  --path <path-to-workspace>/MyFirstApp --activity MainActivity \

6.  --package com.example.myfirstapp

Replace <target-id> with an id from the list of targets (from the previous step) and replace <path-to-workspace> with the location in which you want to save your Android projects.

Create a Project with Command Line Tools

---

If you're not using the Eclipse IDE with the ADT plugin, you can instead create your project using the SDK tools from a command line:

1.    Change directories into the Android SDK’s tools/ path.

2.    Execute:

android list targets

This prints a list of the available Android platforms that you’ve downloaded for your SDK. Find the platform against which you want to compile your app. Make a note of the target id. We recommend that you select the highest version possible. You can still build your app to support older versions, but setting the build target to the latest version allows you to optimize your app for the latest devices.

If you don't see any targets listed, you need to install some using the Android SDK Manager tool. See Adding Platforms and Packages.

3.    Execute:

4.  android create project --target <target-id> --name MyFirstApp \

5.  --path <path-to-workspace>/MyFirstApp --activity MainActivity \

6.  --package com.example.myfirstapp

Replace <target-id> with an id from the list of targets (from the previous step) and replace <path-to-workspace> with the location in which you want to save your Android projects.

Running Your 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 andandroid: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="19" />

    ...

</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.