Hola Android -- Stage 2

Ok, so you've got your first Android application that prints 'Hello World'; nothing to write home about.

Let's expand on it a bit and make use of some of the User Interface capabilities. First though, let's remove the printing of 'Hello World'.

If you search the code you'll find no reference to our elusive string, instead it's hiding in the resources layout definition file res/layout/main.xml.

user@River:~/HolaAndroid$ cat -n res/layout/main.xml
1  <?xml version="1.0" encoding="utf-8"?>
2  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3      android:orientation="vertical"
4      android:layout_width="fill_parent"
5      android:layout_height="fill_parent"
6      >
7  <TextView
8      android:layout_width="fill_parent"
9      android:layout_height="wrap_content"
10      android:text="Hello World, HolaAndroid"
11      />
12  </LinearLayout>
13
user@River:~/HolaAndroid$

Removing line 10 and you'll now have an application that renders a blank screen. Rebuild and re-run and you'll get:

user@River:~/HolaAndroid$ vi res/layout/main.xml
user@River:~/HolaAndroid$ make
ant debug
Buildfile: build.xml
  [setup] Android SDK Tools Revision 6
  [setup] Project Target: Android 1.5
  [setup] API level: 3
  [setup] WARNING: No minSdkVersion value set. Application will install on all Android versions.
  [setup] Importing rules file: platforms/android-3/ant/ant_rules_r2.xml

-compile-tested-if-test:

-dirs:
   [echo] Creating output directories if needed...

-resource-src:
   [echo] Generating R.java / Manifest.java from the resources...

-aidl:
   [echo] Compiling aidl files into Java classes...

compile:
  [javac] Compiling 1 source file to /home/user/HolaAndroid/bin/classes

-dex:
   [echo] Converting compiled files and external libraries into /home/user/HolaAndroid/bin/classes.dex...

-package-resources:
   [echo] Packaging resources
[aaptexec] Creating full resource package...

-package-debug-sign:
[apkbuilder] Creating HolaAndroid-debug-unaligned.apk and signing it with a debug key...
[apkbuilder] Using keystore: /home/user/.android/debug.keystore

debug:
   [echo] Running zip align on final apk...
   [echo] Debug Package: /home/user/HolaAndroid/bin/HolaAndroid-debug.apk

BUILD SUCCESSFUL
Total time: 1 second
user@River:~/HolaAndroid$ make run
adb install -r ./bin/HolaAndroid-debug.apk
97 KB/s (4342 bytes in 0.043s)
 pkg: /data/local/tmp/HolaAndroid-debug.apk
Success
adb shell am start -a android.intent.action.HolaAndroid -n com.example.holaandroid/com.example.holaandroid.HolaAndroid
Starting: Intent { act=android.intent.action.HolaAndroid cmp=com.example.holaandroid/.HolaAndroid }
user@River:~/HolaAndroid$

Now, you can play with your screen design by editing the res/layout/main.xml file. Note below we've added lines 11-15 to add a button to the main window.

user@River:~/HolaAndroid$ cat -n res/layout/main.xml
1    <?xml version="1.0" encoding="utf-8"?>
2    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3        android:orientation="vertical"
4        android:layout_width="fill_parent"
5        android:layout_height="fill_parent"
6        >
7    <TextView
8        android:layout_width="fill_parent"
9        android:layout_height="wrap_content"
10        />
11    <Button android:id="@+id/button1"
12        android:layout_width="fill_parent"
13        android:layout_height="wrap_content"
14        android:layout_alignParentBottom="true"
15        android:text="Menu1" />
16    </LinearLayout>
user@River:~/HolaAndroid$

Rebuild and run and you'll get:



Alas, while you've created a button, the button has no action associated with it. Press it as you'd like you'll never get it to do anything.

So, let's make it do something. In order to tie your newly created button to an action you'll need to edit the src/com/example/holaandroid/HolaAndroid.java source. We'll add a button member, or attribute, and assign an action method to be called on the button click.

Below is our modified source code:

user@River:~/HolaAndroid$ cat -n src/com/example/holaandroid/HolaAndroid.java 
     1  package com.example.holaandroid;
     2
     3  import android.app.Activity;
     4  import android.os.Bundle;
     5  import android.widget.Button;
     6  import android.view.View;
     7  import android.view.View.OnClickListener;
     8  import android.util.Log;
     9
    10  public class HolaAndroid extends Activity
    11  {
    12      private static final String ClassName = "HolaAndroid";
    13      private Button b1_;
    14
    15      /** Called when the activity is first created. */
    16      @Override
    17      public void onCreate(Bundle savedInstanceState)
    18      {
    19          final String MethodName = "onStart";
    20
    21          super.onCreate(savedInstanceState);
    22          setContentView(R.layout.main);
    23
    24          b1_ = (Button)this.findViewById(R.id.button1);
    25          b1_.setOnClickListener(new OnClickListener() {
    26                  public void onClick (View v){
    27                    Log.d(ClassName+"::"+MethodName, "entry");
    28                  }
    29              });
    30      }
    31  }
user@River:~/HolaAndroid$ 

Now, if you're running the debugger you'll notice upon button click the debugger will receive a 'D/HolaAndroid::onStart( 1525): entry' message. To make our action a bit more obvious, follow line 27 with:

    ..
    ..
    25         b1_.setOnClickListener(new OnClickListener() {
    26                 public void onClick (View v){
    27                   Log.d(ClassName+"::"+MethodName, "entry");
    28                   finish();
    29                 }
    30             });
    ..
    ..

Now, your application will terminate when you press the button.