android 只有主线程能更新UI

1 Handler handler= new Handler(){
2     @Override
3     public void handleMessage(Message msg){
4         TextView myTextView=(TextView )findViewById(R.id.MyTextView);
5         myTextView.setText("Button Pressed");
6     }
7     };

Runnable runnable=  new Runnable() {
            public void run() {
                
                long endTime=System.currentTimeMillis()+20*1000;
                while (System.currentTimeMillis()<endTime) 
                {
                    synchronized (this) {
                        try {
                               wait(endTime - System.currentTimeMillis());
                             } catch (Exception e) {
                            }
                        }
                    
                    handler.sendEmptyMessage(0);
                }
            }
        } ;
        
        
        Thread thread=new Thread(runnable);
        thread.start();