Clicking the back button twice to exit an activity

Question

I've noticed this pattern in a lot of Android apps and games recently: when clicking the back button to "exit" the application, a Toast comes up with a message similar to "Please click BACK again to exit".

I was wondering, as I'm seeing it more and more often, is that a built-in feature that you can somehow access in an activity? I've looked at the source code of many classes but I can't seem to find anything about that.

Of course, I can think about a few ways to achieve the same functionality quite easily (the easiest is probably to keep a boolean in the activity that indicates whether the user already clicked once...) but I was wondering if there's something already here.

EDIT: As @LAS_VEGAS mentioned, I didn't really mean "exit" in the traditional meaning. (i.e. terminated) I meant "going back to whatever was open before the application start activity was launched", if that makes sense :)

Answer 1

In Java Activity:

boolean doubleBackToExitPressedOnce = false;

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

    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();

    new Handler().postDelayed(new Runnable() {

        @Override
        public void run() {
            doubleBackToExitPressedOnce=false;                       
        }
    }, 2000);
} 

In Kotlin Activity:

private var doubleBackToExitPressedOnce = false
override fun onBackPressed() {
        if (doubleBackToExitPressedOnce) {
            super.onBackPressed()
            return
        }

        this.doubleBackToExitPressedOnce = true
        Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show()

        Handler().postDelayed(Runnable { doubleBackToExitPressedOnce = false }, 2000)
    }

I Think this handler helps to reset the variable after 2 second.