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.
