Android users click the return key twice to exit

For Android applications, we often need to determine the user's operation on the Return key. Generally, to prevent misoperation, the user is prompted whether to exit the application when the user presses the return key twice in a row.

The basic principle of the first implementation is that when the BACK key is pressed, it will be captured by onKeyDown. If it is determined to be the BACK key, the exit method is executed.
In the exit method, the isExit value is determined first. If it is set to false, the isExit value is set to true. A prompt is displayed, and a message is sent after 2000 milliseconds (2 seconds, in Handler, this value is restored to false. If you press the BACK key again within 2 seconds of the message sending interval, the exit method is executed again. If the value of isExit is already true, the exit method is executed.

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Package com. gaolei. exitdemo; import android. app. activity; import android. OS. bundle; import android. OS. handler; import android. OS. message; import android. view. keyEvent; import android. widget. toast; public class MainActivity extends Activity {// defines a variable to identify whether to exit private static boolean isExit = false; Handler mHandler = new Handler () {@ Override public void handleMessage (Message msg) {super. handleMessage (msg ); IsExit = false ;}}; @ Override protected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. activity_main) ;}@ Override public boolean onKeyDown (int keyCode, KeyEvent event) {if (keyCode = KeyEvent. KEYCODE_BACK) {exit (); return false;} return super. onKeyDown (keyCode, event);} private void exit () {if (! IsExit) {isExit = true; Toast. makeText (getApplicationContext (), "exit the program again", Toast. LENGTH_SHORT ). show (); // use handler to send the change status message mHandler. sendEmptyMessageDelayed (0, 2000);} else {finish (); System. exit (0 );}}}

The second method is to calculate the time difference by recording the key time:

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Package com. gaolei. exitdemo; import android. app. activity; import android. OS. bundle; import android. view. keyEvent; import android. widget. toast; public class MainActivity extends Activity {private long exitTime = 0; @ Override protected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. activity_main) ;}@ Override public boolean onKeyDown (int keyCode, KeyEvent event) {if (keyCode = KeyEvent. KEYCODE_BACK) {exit (); return false;} return super. onKeyDown (keyCode, event);} public void exit () {if (System. currentTimeMillis ()-exitTime)> 2000) {Toast. makeText (getApplicationContext (), "exit the program again", Toast. LENGTH_SHORT ). show (); exitTime = System. currentTimeMillis ();} else {finish (); System. exit (0 );}}}