Android Application Development For Dummies, 2nd Edition

Creating Your First Activity

You may have already created your first activity if you created a project using the New Android Project Wizard in Chapter 3: the MainActivity activity. Open the MainActivity.java file in your project to enhance it in the following sections.

Starting with onCreate

The entry point into your application is the onCreate() method. The code for the MainActivity.java file already contains an implementation of the onCreate() method. It’s where you start writing code! For now, your code should look like this:

public class MainActivity extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

}

You write the initialization code directly below the setContentView() method.

Be sure to always include this method call to your onCreate() method:

super.onCreate(savedInstanceState);

It’s required for the application to run. This line directs the base Activity class to perform setup work for the MainActivity class. If you omit this line of code, you receive a runtime exception.

Telling Android to display the user interface

By default, an activity has no idea what its user interface is. It can be a simple form that allows the user to type information to be saved; a visual, camera-based, augmented, virtual reality application ...