First Steps with the Android SDK - Beginning Android Games - page 35

button= new Button( this );
button.setText( "Touch me!" );
The next line in onCreate() sets the OnClickListener of the Button . OnClickListener is a
callback interface with a single method, OnClickListener.onClick() , which gets called when the
Button is clicked. We want to be notified of clicks, so we let our HelloWorldActivity implement
that interface and register it as the OnClickListener of the Button .
button.setOnClickListener( this );
The last line in the onCreate() method sets the Button as the content View of our Activity .
View s can be nested, and the content View of the Activity is the root of this hierarchy. In our
case, we simply set the Button as the View to be displayed by the Activity . For simplicity's
sake, we won't get into details of how the Activity will be laid out given this content View .
setContentView(button);
}
The next step is simply the implementation of the OnClickListener.onClick() method, which
the interface requires of our Activity . This method gets called each time the Button is clicked.
In this method, we increase the touchCount counter and set the Button 's text to a new string.
public void onClick(View v) {
touchCount++;
button.setText("Touched me"+touchCount+"times");
}
Thus, to summarize our Hello World application, we construct an Activity with a Button .
Each time the Button is clicked, we set its text accordingly. This may not be the most exciting
application on the planet, but it will do for further demonstration purposes.

Note that we never had to compile anything manually. The ADT plug-in, together with Eclipse,
will recompile the project every time we add, modify, or delete a source file or resource. The
result of this compilation process is an APK file ready to be deployed to the emulator or an
Android device. The APK file is located in the bin/ folder of the project.
You'll use this application in the following sections to learn how to run and debug Android
applications on emulator instances and on devices.

Running the Application on a Device or Emulator
Once we've written the first iteration of our application code, we want to run and test it to
identify potential problems or just be amazed at its glory. We have two ways we can achieve this:

We can run our application on a real device connected to the development

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PC via USB.

We can fire up the emulator included in the SDK and test our application there.

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In both cases, we have to do a little bit of setup work before we can finally see our application
in action.