为什么我的线程不起作用？

Question

I make an app that can count down. But it doesn't work and it just shows 100 in textview.

Here is my code:

public class MainActivity extends Activity {

    private TextView textView;
    private Button start;
    Thread thread;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView) findViewById(R.id.textView1);
        start = (Button) findViewById(R.id.button1);
        start.setOnClickListener(onStart);
        thread = new Thread( //it's my thread
                new Runnable() {
                    @Override
                    public void run() {
                        for (int i = 99; i > 0; i--) {
                            Log.i("Where am I?", "I'm in for loop .");
                            try {
                                textView.setText(String.valueOf(i));
                            } catch (Exception e) {
                                Log.e("Exception.getCause", String.valueOf(e.getCause()), e.getCause());
                            }
                            Log.i("INDEX", String.valueOf(i));
                        }
                    }
                });
    }

    private View.OnClickListener onStart = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Log.i("Where am I?", "I in View.OnClickListener .");
            thread.start();
        }
    };
}

Answer 1

Update your TextView using runOnUiThread as below...

runOnUiThread(new Runnable() {
   @Override    
   public void run() {

       textView.setText(String.valueOf(i));

   }
});

Update:

For delay in count you can use Handler as below. Create an object of Handler and create a Thread .

private Handler mTimerHandler = new Handler();

private Runnable mTimerExecutor = new Runnable() {

    @Override
    public void run() {

         //add your code here which should execute after the specified delay

    }
};

Then pass that thread inside postDelayed() method Handler with the time which should be delayed to execute the thread as below...

mTimerHandler.postDelayed(mTimerExecutor, 1000);

And if you want to cancel the thread to execute, use removeCallbacks() method as below...

mTimerHandler.removeCallbacks(mTimerExecutor);

Answer 2

Catching for Exception inside the Thread is kind of misleading. As matter of fact, textView.setText(String.valueOf(i)); executed in a Thread different from the UI Thread should make you app crashes for CalledFromTheWrongThreadException . You should use an Handler to execute that line in the UI Thread's context

Answer 3

textView.setText(String.valueOf(i));

必须仅在UI线程中使用。

Answer 4

textView.setText(String.valueOf(i)); 

This is UI action, You can handle UI action only in a main thread.

You can send a message to the handle of activity.

Answer 5

You cannot use Thread class to interact with UI you should use AsyncTask or Handler classes. Sample tutorial: http://www.vogella.com/tutorials/AndroidBackgroundProcessing/article.html

Answer 6

Use AsyncTask instead.

Checkout:

http://www.vogella.com/tutorials/AndroidBackgroundProcessing/article.html