<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="horizontal" >

  <Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="clickButton"
    android:text="开始计时" />


</LinearLayout>

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;

public class FirstActivity extends Activity{

  private Button button;
  private int count = 60;
  private int COUNT_TIME = 0;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.first_activity);
    button = (Button) findViewById(R.id.button);

  }

  private Handler handler = new Handler(){

    @Override
    public void handleMessage(Message msg) {
      if(count <= 0){
        count = 60;
        button.setText("重新计时");
        button.setClickable(true);
        return;
      }
      count--;
      button.setText(""+count);
      sendEmptyMessageDelayed(COUNT_TIME,1000);
    }
  };

  public void clickButton(View view){
    handler.sendEmptyMessage(COUNT_TIME);
    button.setClickable(false);
  }
}

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;

public class FirstActivity extends Activity{

  private Button button;
  private int count = 30;
  private int COUNT_TIME = 0;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.first_activity);
    button = (Button) findViewById(R.id.button);

  }

  private Handler handler = new Handler(){

    @Override
    public void handleMessage(Message msg) {
      button.setText(""+count);
      if(count <= 0){
        count = 30;
        button.setClickable(true);
        button.setText("重新计时");
        timerTask.cancel(); //取消该任务
      }
    }
  };

  private Timer timer = new Timer();
  private TimerTask timerTask;
  public void clickButton(View view){
    button.setClickable(false);

    timerTask = new TimerTask() {

      @Override
      public void run() {
        count--;
        handler.sendEmptyMessage(COUNT_TIME);
      }
    };
    timer.schedule(timerTask,0,1000); //0秒后，每过一秒钟执行一次该任务
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();
    //释放资源
    if(timerTask != null){
      timerTask.cancel();
      timerTask = null;
    }
    if(timer != null){
      timer.cancel();
      timer = null;
    }
  }
}

import android.app.Activity;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.view.View;
import android.widget.Button;

public class FirstActivity extends Activity{

  private Button button;

  private CountDownTimer timer;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.first_activity);
    button = (Button) findViewById(R.id.button);

  }

  public void clickButton(View view){
    button.setClickable(false);
    //第一个参数：倒计时的毫秒数；第二个参数：接收onTick回调的时间间隔
    timer = new CountDownTimer(30000, 10) {
       public void onTick(long millisUntilFinished) {
         button.setText(millisUntilFinished / 1000 + "秒");
       }
       public void onFinish() {
         button.setText("重新计时");
         button.setClickable(true);
       }
     };
    timer.start();
  }
  @Override
  protected void onDestroy() {
    super.onDestroy();
    if(timer != null){
      timer.cancel();
    }
  }
}