安卓handler.post问题

 protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         btn = (Button) findViewById(R.id.button1);
         progressBar = (ProgressBar) findViewById(R.id.progressBar1);

         btn.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View v) {
                 // 立即把消息加到消息队列中,postDelayed(r,3000)延迟3秒加到消息队列
                 handler.post(r);
             }
         });
     }

     Handler handler = new Handler() {
         public void handleMessage(android.os.Message msg) {
             progressBar.setProgress(msg.arg1);
             handler.post(r);

             if (i == 80)
                 // 移除消息
                 handler.removeCallbacks(r);
         };

     };
     int i = 0;
     Runnable r = new Runnable() {

         @Override
         public void run() {
             i = i + 10;
             message = new Message();
             message.arg1 = i;

             try {
                 Thread.sleep(1000);
             } catch (InterruptedException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }

             handler.sendMessage(message);

         }
     };
 }

在第11行不是使用post启动线程r了吗,为什么在第19行还要再post一次??求指点