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