postDelayed方法和removeCallbacks方法的使用

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方法postDelayed的作用是延迟多少毫秒后开始运行，而removeCallbacks方法是删除指定的Runnable对象，使线程对象停止运行。

方法声明如下：

public final boolean postDelayed (Runnable r, long delayMillis)

其中参数Runnable r在Handler对象所运行的线程中执行。

创建名称为handler2的Android项目，Main.java的核心代码如下：

public class Main extends Activity {
    private Button button1;
    private Button button2;

     private Handler handler = new Handler();

     private int count = 0;

     private Runnable runnableRef = new Runnable() {
        public void run() {
            Log.v("2", Thread.currentThread().getName());
            count++;
             Log.v("!", "count=" + count);
            handler.postDelayed(runnableRef, 1000);
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Log.v("1", Thread.currentThread().getName());

         button1 = (Button) this.findViewById(R.id.button1);
         button2 = (Button) this.findViewById(R.id.button2);

        button1.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {
                 Thread thread = new Thread(runnableRef);
                thread.start();
                Log.v("!!!!!!!!!!!!!", "end");
            }
        });

        button2.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {
                handler.removeCallbacks(runnableRef);
            }
        });

    }
}

 

程序运行后单击button1按钮开始循环，count累加1，运行结果如图6.41所示。

图6.41  循环加1效果

from:http://book.51cto.com/art/201211/363310.htm