Does pressing Back always cause Activity to finish()?

Question

I've heard that pressing the back button will essentially cause the current Activity to finish(). Is this always the case? Seems like it would be with the way it pops the Activity off the stack.

The one situation I'm not so sure about is when the root Activity in a Task has back pressed. I'm currently experiencing a very weird effect, described as follows:

On loading my application, the first Activity is for initialization, and once it finishes, it calls my main Activity (a TabActivity). This first init activity has android:noHistory="true" set in the Manifest so pressing Back from my main Activity won't go back to that. It goes to the Launcher. When I click on my App in the Launcher a second time, the initialization activity loads again, and loads the main Activity when done. Almost immediately after, it loads a second instance of my main Activity. But ONLY after the Application has already been run once, and was exited by pressing BACK from the main Activity. It does it every subsequent time until I force quit the app or load a new version from the IDE.

Based on this, I am suspecting some kind of Activity instance is lying around and being reused, since it only happens on the second+ time I run the application (and exit with BACK -- using HOME just returns to the last state of the app, no big deal). Anyone have any thoughts??

Answer 1

I've heard that pressing the back button will essentially cause the current Activity to finish(). Is this always the case?

No it is not. The most activities have this behaviour but not all. For example you could create a Dialog and set it setCancelable(false) and it won't close if you click BACK button.

Furthermore you could customize activity behaviour on BACK button pressed by overriding onBackPressed

Called when the activity has detected the user's press of the back key. The default implementation simply finishes the current activity, but you can override this to do whatever you want.

About your application behaviour..Did you verify if the activity launcher is finished after it loads your main activity? I mean if the onDestroy() method is called. Maybe after it runs the main activity it remains there and when you click back you just go back to the old Launcher...

hope this helps..

Answer 2

Read through the Activity and Task design guidelines on the Android developer site; they explain how the Home and Back buttons work. Obviously, if you override the default behavior (as mentioned by hara above), the back button will not finish the activity.

On your specific issue, check your logcat. You should be able to see there whether it is bringing an old process back to life or starting up a new one. If that is unclear, insert a couple of log statements into onCreate, onPause, onDestroyed, etc., so that you can see exactly what is happening with your process.

Answer 3

You can control BACK-BUTTON by writing the following code.

public boolean onKeyDown(int keyCode, KeyEvent event) 
{
    if (keyCode == KeyEvent.KEYCODE_BACK ) {
        //preventing default implementation previous to 
        //android.os.Build.VERSION_CODES.ECLAIR
        return false;
    }     
    return super.onKeyDown(keyCode, event);    
}