[java] Clicking the back button twice to exit an activity

Recently, I needed to implement this back button feature in an app of mine. The answers on the original question were useful, but I had to take two more points into consideration:

1. At some points in time, the back button is disabled
2. The main activity is using fragments in combination with a back stack

Based on the answers and comments, I created the following code:

private static final long BACK_PRESS_DELAY = 1000;

private boolean mBackPressCancelled = false;
private long mBackPressTimestamp;
private Toast mBackPressToast;

@Override
public void onBackPressed() {
    // Do nothing if the back button is disabled.
    if (!mBackPressCancelled) {
        // Pop fragment if the back stack is not empty.
        if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
            super.onBackPressed();
        } else {
            if (mBackPressToast != null) {
                mBackPressToast.cancel();
            }

            long currentTimestamp = System.currentTimeMillis();

            if (currentTimestamp < mBackPressTimestamp + BACK_PRESS_DELAY) {
                super.onBackPressed();
            } else {
                mBackPressTimestamp = currentTimestamp;

                mBackPressToast = Toast.makeText(this, getString(R.string.warning_exit), Toast.LENGTH_SHORT);
                mBackPressToast.show();
            }
        }
    }
}

The code above assumes that the support library is used. If you use fragments but not the support library, you want to replace getSupportFragmentManager() by getFragmentManager().

Remove the first if, if the back button is never cancelled. Remove the second if, if you don`t use fragments or a fragment back stack

Also, it is important to be aware that the method onBackPressed is supported since Android 2.0. Check this page for an elaborate description. To make the back press feature work on older versions as well, add the following method to your activity:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
    if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.ECLAIR
            && keyCode == KeyEvent.KEYCODE_BACK
            && event.getRepeatCount() == 0) {
        // Take care of calling this method on earlier versions of
        // the platform where it doesn't exist.
        onBackPressed();
    }

    return super.onKeyDown(keyCode, event);
}