multithreading - Android update TextView in Thread and Runnable

Question

I want to make a simple timer in Android that updates a TextView every second. It simply counts seconds like in Minesweeper.

The problem is when i ignore the tvTime.setText(...) (make it //tvTime.setText(...), in LogCat will be printed the following number every second. But when i want to set this number to a TextView (created in another Thread), the program crashes.

Does anyone have an idea how to solve this easily?

Here's the code (method is called on startup):

private void startTimerThread() {
    Thread th = new Thread(new Runnable() {
        private long startTime = System.currentTimeMillis();
        public void run() {
            while (gameState == GameState.Playing) {
                System.out.println((System.currentTimeMillis() - this.startTime) / 1000);
                tvTime.setText("" + ((System.currentTimeMillis() - this.startTime) / 1000));
                try {
                    Thread.sleep(1000);
                }
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    th.start();
}

EDIT:

Finally, I got it. Here is the solution, for those who are interested in.

private void startTimerThread() {       
    Thread th = new Thread(new Runnable() {
        private long startTime = System.currentTimeMillis();
        public void run() {
            while (gameState == GameState.Playing) {                
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        tvTime.setText(""+((System.currentTimeMillis()-startTime)/1000));
                    }
                });
                try {
                    Thread.sleep(1000);
                } 
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    th.start();
}

Answer 1

The UserInterface can only be updated by the UI Thread. You need a Handler, to post to the UI Thread:

private void startTimerThread() {
    Handler handler = new Handler();
    Runnable runnable = new Runnable() {
        private long startTime = System.currentTimeMillis();
        public void run() {
            while (gameState == GameState.Playing) {  
                try {
                    Thread.sleep(1000);
                }    
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
                handler.post(new Runnable(){
                    public void run() {
                       tvTime.setText("" + ((System.currentTimeMillis() - this.startTime) / 1000));
                }
            });
            }
        }
    };
    new Thread(runnable).start();
}