Rectangle 27 156

Sudheesh B Nair's has a nice (and accepted) answer on the question, which i think should have a better alternative such as;

What's wrong with measuring time passed and checking if TIME_INTERVAL miliseconds (say 2000) passed since the last back press. The following sample code uses System.currentTimeMillis(); to store the time onBackPressed() is called;

private static final int TIME_INTERVAL = 2000; // # milliseconds, desired time passed between two back presses.
private long mBackPressed;

@Override
public void onBackPressed()
{
    if (mBackPressed + TIME_INTERVAL > System.currentTimeMillis()) 
    { 
        super.onBackPressed(); 
        return;
    }
    else { Toast.makeText(getBaseContext(), "Tap back button in order to exit", Toast.LENGTH_SHORT).show(); }

    mBackPressed = System.currentTimeMillis();
}

Back on accepted answer critique; Using a flag to indicate if it was pressed in last TIME_INTERVAL (say 2000) milliseconds and set - reset is via Handler's postDelayed() method was the first thing to come in my mind. But the postDelayed() action should be cancelled when activity is closing, removing the Runnable.

In order to remove the Runnable, it must not be declared anonymous, and be declared as member along with the Handler aswell. Then removeCallbacks() method of Handler can be called appropriately.

The following sample is the demonstration;

private boolean doubleBackToExitPressedOnce;
private Handler mHandler = new Handler();

private final Runnable mRunnable = new Runnable() {
    @Override
    public void run() {
        doubleBackToExitPressedOnce = false;                       
    }
};

@Override 
protected void onDestroy() 
{ 
    super.onDestroy();

    if (mHandler != null) { mHandler.removeCallbacks(mRunnable); }
}

@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();

    mHandler.postDelayed(mRunnable, 2000);
}

Thanks to @NSouth for contributing; In order to prevent toast message appearing even after the application is closed, Toast can be declared as a member - say mExitToast - and can be cancelled via mExitToast.cancel(); just before super.onBackPressed(); call.

For the ones who think that it's the same what Sudheesh B Nair said: Same functionality, better performance. so +1.

The first code block has the best answer.

I like this answer and I think it's the best. I mean i don't THINK it is, IT IS the best answer, for the reasons stated above. I hope you get more upvotes for this one. One comment though: no one finds it a it odd that the toast persists a couple of seconds after the app closes? No one cares to cancel the toast? I know it may be a small detail but I think that should happen. What do you guys think?

@NSouth Second code block was a sample using mHandlers in order to show it required more effort. I suggest you consider using the first code block, which doesn't use a handler.

java - Clicking the back button twice to exit an activity - Stack Over...

java android back-button