定时运行在一段时候后停止的倒计时，在倒计时运行过程中会在固定间隔时间得到通知（译者：触发onTick方法），以下的样例显示在一个文本框中显示一个30s倒计时： 

 new CountdownTimer(30000, 1000) {
      public void onTick(long millisUntilFinished) {
          mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
      }
      public void onFinish() {
          mTextField.setText("done!");
      }
  }.start();

onTick的调用是同步的，保证这次调用不会在之前调用完毕前发生。这里的同步机制主要是用来：onTick的实现须要非常多时间运行比倒计时间隔更重要的事情。 

构造函数 

         public CountDownTimer (long millisInFuture, long countDownInterval) 

參数 

                   millisInFuture  从開始调用start()到倒计时完毕并onFinish()方法被调用的毫秒数。（译者注：倒计时时间，单位毫秒） 

                   countDownInterval  接收onTick(long)回调的间隔时间。（译者注：单位毫秒） 

公共方法 

public final void cancel () 

         取消倒计时（译者：取消后，再次启动会又一次開始倒计时）        

                  

public abstract void onFinish () 

         倒计时完毕时被调用    

public abstract void onTick (long millisUntilFinished) 

         固定间隔被调用 

參数 

                            millisUntilFinished   倒计时剩余时间。 

public synchronized final CountDownTimer start () 

         启动倒计时 

 import android.app.Activity;
 import android.os.Bundle;
 import android.os.CountDownTimer;
 import android.util.Log;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.TextView;

 import com.test.R;

 public class CountDownTimeActivity extends Activity implements OnClickListener {

     TextView mTextView;
     Button mButton1;
     Button mButton2;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.countdown);

        mTextView = (TextView)findViewById(R.id.textView1);
        mButton1 = (Button)findViewById(R.id.button1);
        mButton2 = (Button)findViewById(R.id.button2);
        mButton1.setOnClickListener(this);
        mButton2.setOnClickListener(this);
     }

     CountDownTimer timer = new CountDownTimer(40000,1000) {

        @Override
        public void onTick(long millisUntilFinished) {
            mTextView.setText("seconds remaining: " + millisUntilFinished / 1000);
            try {
               Thread.sleep(1200);
            } catch (InterruptedException e) {
               e.printStackTrace();
            }
            Log.e("CountDown",millisUntilFinished+"");
        }

        @Override
        public void onFinish() {
            mTextView.setText("done！");
        }
     };

     @Override
     public void onClick(View v) {
        switch(v.getId()){
        case R.id.button1:
            timer.start();
            break;
        case R.id.button2:
            timer.cancel();
            break;
        }

     }
 }