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();
        }
    }
}

Chinaman

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);

Space

@Space said that "handler to run the very same Runnable after 1000 milliseconds" ,but the Runnable also includes the gameover() method that should be executed each time whenever the run method executes. – Fico

Isn't the gameOver() called infinitely every second, rather than being called twice? It looks like infinite recursion. – Crispen

Answer 2

Below is the code that I use which works same as the accepted answer but is quite simple to write and understand.

final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
    @Override
    public void run() {
        // Write whatever to want to do after delay specified (1 sec)
        Log.d("Handler", "Running Handler");
    }
}, 1000);

Larcenous

Answer 3

Thread(Runnable {
    // background work here ... 
    Handler(Looper.getMainLooper()).postDelayed(Runnable {
        // Update UI here ...
    }, 10000) // It will wait 10 sec before updating UI
}).start()

Peterman

Answer 4

Using a parameterless Handler constructor is deprecated, and not using lambdas also make the code look clunky, so with that being said, here's how it looks a more modern use:

final Runnable _r_ = new Runnable(){...};

Handler handler = new Handler(Looper.getMainLooper());
handler.postDelayed(() -> _r_.run(), 666);

You might also update it to use method reference

handler.postDelayed(_r_::run(), 666);

Or more simple with just a qualifier

handler.postDelayed(_r_, 666);

Kodok

Answer 5

Saw this example, should be as easy as that :

Handler().postDelayed({
    val intent = Intent(this, MainActivity::class.java)
    startActivity(intent)
    finish()
}, 4000) // delaying for 4 seconds...

Psychosurgery