Android Android programming without an IDE


Example

This is a minimalist Hello World example that uses only the most basic Android tools.

Requirements and assumptions

This example assumes Linux. You may have to adjust the syntax for your own platform.

Setting up the Android SDK

After unpacking the SDK release:

  1. Install additional packages using the SDK manager. Don't use android update sdk --no-ui as instructed in the bundled Readme.txt; it downloads some 30 GB of unnecessary files. Instead use the interactive SDK manager android sdk to get the recommended minimum of packages.

  2. Append the following JDK and SDK directories to your execution PATH. This is optional, but the instructions below assume it.

    • JDK/bin
    • SDK/platform-tools
    • SDK/tools
    • SDK/build-tools/LATEST (as installed in step 1)
  3. Create an Android virtual device. Use the interactive AVD Manager (android avd). You might have to fiddle a bit and search for advice; the on-site instructions aren't always helpful.

    (You can also use your own device)

  4. Run the device:

    emulator -avd DEVICE
    
  5. If the device screen appears to be locked, then swipe to unlock it.

    Leave it running while you code the app.

Coding the app

  1. Change to an empty working directory.

  2. Make the source file:

    mkdir --parents src/dom/domain
    touch src/dom/domain/SayingHello.java
    

    Content:

    package dom.domain;
    import android.widget.TextView;
    
    public final class SayingHello extends android.app.Activity
    {
        protected @Override void onCreate( final android.os.Bundle activityState )
        {
            super.onCreate( activityState );
            final TextView textV = new TextView( SayingHello.this );
            textV.setText( "Hello world" );
            setContentView( textV );
        }
    }
    
  3. Add a manifest:

    touch AndroidManifest.xml
    

    Content:

    <?xml version='1.0'?>
    <manifest xmlns:a='http://schemas.android.com/apk/res/android'
     package='dom.domain' a:versionCode='0' a:versionName='0'>
        <application a:label='Saying hello'>
            <activity a:name='dom.domain.SayingHello'>
                 <intent-filter>
                    <category a:name='android.intent.category.LAUNCHER'/>
                    <action a:name='android.intent.action.MAIN'/>
                    </intent-filter>
                </activity>
            </application>
        </manifest>
    
  4. Make a sub-directory for the declared resources:

    mkdir res
    

    Leave it empty for now.

Building the code

  1. Generate the source for the resource declarations. Substitute here the correct path to your SDK, and the installed API to build against (e.g. "android-23"):

    aapt package -f \
      -I SDK/platforms/android-API/android.jar \
      -J src -m \
      -M AndroidManifest.xml -S res -v
    

    Resource declarations (described further below) are actually optional. Meantime the above call does nothing if res/ is still empty.

  2. Compile the source code to Java bytecode (.java → .class):

    javac \
      -bootclasspath SDK/platforms/android-API/android.jar \
      -classpath src -source 1.7 -target 1.7 \
      src/dom/domain/*.java
    
  3. Translate the bytecode from Java to Android (.class → .dex):

    First using Jill (.class → .jayce):

    java -jar SDK/build-tools/LATEST/jill.jar \
      --output classes.jayce src
    

    Then Jack (.jayce → .dex):

    java -jar SDK/build-tools/LATEST/jack.jar \
      --import classes.jayce --output-dex .
    

    Android bytecode used to be called "Dalvik executable code", and so "dex".

    You could replace steps 11 and 12 with a single call to Jack if you like; it can compile directly from Java source (.java → .dex). But there are advantages to compiling with javac. It's a better known, better documented and more widely applicable tool.

  4. Package up the resource files, including the manifest:

    aapt package -f \
      -F app.apkPart \
      -I SDK/platforms/android-API/android.jar \
      -M AndroidManifest.xml -S res -v
    

    That results in a partial APK file (Android application package).

  5. Make the full APK using the ApkBuilder tool:

    java -classpath SDK/tools/lib/sdklib.jar \
      com.android.sdklib.build.ApkBuilderMain \
      app.apkUnalign \
      -d -f classes.dex -v -z app.apkPart
    

    It warns, "THIS TOOL IS DEPRECATED. See --help for more information." If --help fails with an ArrayIndexOutOfBoundsException, then instead pass no arguments:

    java -classpath SDK/tools/lib/sdklib.jar \
      com.android.sdklib.build.ApkBuilderMain
    

    It explains that the CLI (ApkBuilderMain) is deprecated in favour of directly calling the Java API (ApkBuilder). (If you know how to do that from the command line, please update this example.)

  6. Optimize the data alignment of the APK (recommended practice):

    zipalign -f -v 4 app.apkUnalign app.apk
    

Installing and running

  1. Install the app to the Android device:

    adb install -r app.apk
    
  2. Start the app:

    adb shell am start -n dom.domain/.SayingHello
    

    It should run and say hello.

That's all. That's what it takes to say hello using the basic Android tools.

Declaring a resource

This section is optional. Resource declarations aren't required for a simple "hello world" app. If they aren't required for your app either, then you could streamline the build somewhat by omitting step 10, and removing the reference to the res/ directory from step 13.

Otherwise, here's a brief example of how to declare a resource, and how to reference it.

  1. Add a resource file:

    mkdir res/values
    touch res/values/values.xml
    

    Content:

    <?xml version='1.0'?>
    <resources>
        <string name='appLabel'>Saying hello</string>
    </resources>
    
  2. Reference the resource from the XML manifest. This is a declarative style of reference:

    <!-- <application a:label='Saying hello'> -->
         <application a:label='@string/appLabel'>
    
  3. Reference the same resource from the Java source. This is an imperative reference:

    // v.setText( "Hello world" );
       v.setText( "This app is called "
         + getResources().getString( R.string.appLabel ));
    
  4. Test the above modifications by rebuilding, reinstalling and re-running the app (steps 10-17).

    It should restart and say, "This app is called Saying hello".

Uninstalling the app

adb uninstall dom.domain

See also