Android: Catch Back Button

Your intend can be implemented without further ado. You have only to override the event onBackPressed(), which is executed when the back button is clicked. Just copy the following lines into the code of your respective activity:

@Override
public void onBackPressed() {
    super.onBackPressed();
}

With this, the behavior of your app is like ever before. The super.onBackPressed() ensures that the default action of the back button is still running. But if you omit this line, nothing happens when clicking on the back button.

What you also need is a condition deciding which action should be executed by clicking the back button. For this, we are introducing the variable canClose.

private boolean canClose = true;

public void showDetails() {
   // Code to display the detailed view
   canClose = false;
}

public void showOverview() {
   // Code to display the overview
   canClose = true;
}

@Override
public void onBackPressed() {
    if (canClose) {
        super.onBackPressed();
    } else {
        showOverview();       
    }
}

We declare the canClose-variable directly in our activity and set it to true at the beginning. That means, when clicking the back button immediately after starting the app, this would close the application.

But, if we select some of the details after starting the app (showDetails), we temporarily set canClose to false. This has the effect, that with an open detail view, clicking the back button first shows the overview (showOverview). At the same time, we set canClose to ture, so that the next click on the back button actually closes the entire app.
2013-10-05 at 13:34