java - Check if back key was pressed in android?

Question

Say I'm on my main activity and I start a new activity

MainActivity > NewActivity

And from NewActivity I press the back key

MainActivity < NewActivity

I want MainActivity to do something if it's being displayed after NewActivity is closed, but not when MainActivity is run normally, such as when first running the application. Does anyone know if this is possible?

Answer 1

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK)) {
        Log.d(this.getClass().getName(), "back button pressed");
    }
    return super.onKeyDown(keyCode, event);
}

@Update. If you want to be notified when NewActivity is finished, you have to start it by startActivityForResult(Intent, requestCode). Then, you must override onActivityResult() on MainActivity. Check the requestcode parameter here, if the return code equals the submit code (when you start childActivity), put some code to do your business.

int MYCODE=1000;
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Result OK.d.
    if (requestCode == MYCODE) {
        // do something good
    }
}