how to use postDelayed() correctly in android studio?

Question

I have a countDownTimer and if the user does not hit the gameButton within the 12th second I want the gameOver method called.

The problem is that either the game function instantly gets called when the countDownTimer is 12 or the timer just keeps counting down.

So I am trying to use the postDelayed() method to give the user a full second to hit the button and let the countDownTimer continue, but as my code is right now the game stops on 12 regardless.

import android.app.Activity; import android.os.CountDownTimer; import android.os.Handler; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.TextView; import android.widget.Toast;  public class GameScreen extends Activity {     private TextView time;     private Button start;     private Button cancel;     private Button gameButton;     private CountDownTimer countDownTimer;     public static int count = 0;     public static int countFail = 0;      final Handler handler = new Handler();     final Runnable r = new Runnable() {         public void run() {             handler.postDelayed(this, 1000);             gameOver();         }     };      private View.OnClickListener btnClickListener = new View.OnClickListener() {         @Override         public void onClick(View v) {             switch(v.getId()){                 case R.id.start_ID :                     start();                     break;                 case R.id.cancel :                     cancel();                     break;                 case R.id.gameButton_ID :                     gameButton();                     break;             }         }     };       @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_game_screen);          start = (Button) findViewById(R.id.start_ID);         start.setOnClickListener(btnClickListener);         cancel = (Button) findViewById(R.id.cancel);         cancel.setOnClickListener(btnClickListener);         time = (TextView) findViewById(R.id.time);         gameButton = (Button) findViewById(R.id.gameButton_ID);         gameButton.setOnClickListener(btnClickListener);     }      public void start() {         time.setText("16");         //This doesn't work and makes app crash when you hit start button         countDownTimer = new CountDownTimer(16 * 1000, 1000) {             @Override             public void onTick(long millsUntilFinished) {                 time.setText("" + millsUntilFinished / 1000);                  //turns textview string to int                 int foo = Integer.parseInt(time.getText().toString());                  if (time.getText().equals("12")) {                     r.run();                 }             }              public void onFinish() {                 time.setText("Done !");             }         };         countDownTimer.start();     }      private void cancel() {         if(countDownTimer != null){             countDownTimer.cancel();             countDownTimer = null;         }     }      private void gameOver() {         Toast.makeText(getApplicationContext(), "You scored " + count, Toast.LENGTH_SHORT).show();         count = 0;         countFail = 0;         cancel();     }      private void gameButton() {         int foo = Integer.parseInt(time.getText().toString());          if(foo  % 2 == 0 ) {             Toast.makeText(getApplicationContext(), "PASS", Toast.LENGTH_SHORT).show();             handler.removeCallbacks(r);             ++count;         }         else {             gameOver();         }     } } 

Answer 1

You're almost using postDelayed(Runnable, long) correctly, but just not quite. Let's take a look at your Runnable.

final Runnable r = new Runnable() {     public void run() {         handler.postDelayed(this, 1000);         gameOver();     } }; 

When we call r.run(); the first thing it's going to do is tell your handler to run the very same Runnable after 1000 milliseconds, and then to call gameOver(). What this will actually result in is your gameOver() method being called twice: once right away, and a second time once the Handler is done waiting 1000 milliseconds.

Instead, you should change your Runnable to this:

final Runnable r = new Runnable() {     public void run() {         gameOver();     } }; 

And call it like this:

handler.postDelayed(r, 1000); 

Hope this helps.