使用CountDownTimer类轻松实现倒计时功能

package com.example.daojishi; 
 
import android.app.Activity; 
import android.os.Bundle; 
import android.os.CountDownTimer; 
import android.util.Log; 
import android.view.View; 
import android.widget.TextView; 
import android.widget.Toast; 
 
/** 
 * 
 * @author baozi 
 * 
 * 倒计时的类 CountDownTimer 
 * 
 */ 
public class MainActivity extends Activity { 
 
  private MyCountDownTimer mc; 
  private TextView tv; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    tv = (TextView) findViewById(R.id.show); 
    mc = new MyCountDownTimer(30000, 1000); 
    mc.start(); 
  } 
 
  public void oncancel(View view) { 
    Toast.makeText(MainActivity.this, "取消", Toast.LENGTH_LONG).show();// toast有显示时间延迟 
    mc.cancel(); 
  } 
 
  public void restart(View view) { 
    Toast.makeText(MainActivity.this, "重新开始", Toast.LENGTH_LONG).show();// toast有显示时间延迟 
    mc.start(); 
  } 
 
  /** 
   * 继承 CountDownTimer 防范 
   * 
   * 重写 父类的方法 onTick() 、 onFinish() 
   */ 
 
  class MyCountDownTimer extends CountDownTimer { 
    /** 
     * 
     * @param millisInFuture 
     *      表示以毫秒为单位 倒计时的总数 
     * 
     *      例如 millisInFuture=1000 表示1秒 
     * 
     * @param countDownInterval 
     *      表示 间隔 多少微秒 调用一次 onTick 方法 
     * 
     *      例如: countDownInterval =1000 ; 表示每1000毫秒调用一次onTick() 
     * 
     */ 
    public MyCountDownTimer(long millisInFuture, long countDownInterval) { 
      super(millisInFuture, countDownInterval); 
    } 
 
    @Override 
    public void onFinish() { 
      tv.setText("done"); 
    } 
 
    @Override 
    public void onTick(long millisUntilFinished) { 
      Log.i("MainActivity", millisUntilFinished + ""); 
      tv.setText("倒计时(" + millisUntilFinished / 1000 + ")..."); 
    } 
  } 
} 
//┏┓　　　┏┓ 
//┏┛┻━━━┛┻┓ 
//┃　　　　　　　┃ 　 
//┃　　　━　　　┃ 
//┃　┳┛　┗┳　┃ 
//┃　　　　　　　┃ 
//┃　　　┻　　　┃ 
//┃　　　　　　　┃ 
//┗━┓　　　┏━┛ 
//┃　　　┃  神兽保佑　　　　　　　　 
//┃　　　┃  代码无BUG！ 
//┃　　　┗━━━┓ 
//┃　　　　　　　┣┓ 
//┃　　　　　　　┏┛ 
//┗┓┓┏━┳┓┏┛ 
// ┃┫┫　┃┫┫ 
// ┗┻┛　┗┻┛ 

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  xmlns:tools="http://schemas.android.com/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:paddingBottom="@dimen/activity_vertical_margin" 
  android:paddingLeft="@dimen/activity_horizontal_margin" 
  android:paddingRight="@dimen/activity_horizontal_margin" 
  android:paddingTop="@dimen/activity_vertical_margin" 
  tools:context=".MainActivity" > 
 
  <TextView 
    android:id="@+id/show" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="@string/hello_world" /> 
 
  <Button 
    android:id="@+id/button1" 
    android:onClick="oncancel" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/show" 
    android:layout_below="@+id/show" 
    android:layout_marginLeft="50dp" 
    android:layout_marginTop="106dp" 
    android:text="cancel" /> 
 
  <Button 
    android:id="@+id/button2" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/button1" 
    android:layout_below="@+id/button1" 
    android:layout_marginTop="63dp" 
    android:onClick="restart" 
    android:text="restart" /> 
 
</RelativeLayout> 

/* 
 * Copyright (C) 2008 The Android Open Source Project 
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); 
 * you may not use this file except in compliance with the License. 
 * You may obtain a copy of the License at 
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0 
 * 
 * Unless required by applicable law or agreed to in writing, software 
 * distributed under the License is distributed on an "AS IS" BASIS, 
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 * See the License for the specific language governing permissions and 
 * limitations under the License. 
 */ 
 
package android.os; 
 
import android.util.Log; 
 
/** 
 * Schedule a countdown until a time in the future, with 
 * regular notifications on intervals along the way. 
 * 
 * Example of showing a 30 second countdown in a text field: 
 * 
 * 
 * new CountDownTimer(30000, 1000) { 
 * 
 *   public void onTick(long millisUntilFinished) { 
 *     mTextField.setText("seconds remaining: " + millisUntilFinished / 1000); 
 *   } 
 * 
 *   public void onFinish() { 
 *     mTextField.setText("done!"); 
 *   } 
 * }.start(); 
 * 
 * 
 * The calls to {@link #onTick(long)} are synchronized to this object so that 
 * one call to {@link #onTick(long)} won't ever occur before the previous 
 * callback is complete. This is only relevant when the implementation of 
 * {@link #onTick(long)} takes an amount of time to execute that is significant 
 * compared to the countdown interval. 
 */ 
public abstract class CountDownTimer { 
 
  /** 
   * Millis since epoch when alarm should stop. 
   */ 
  private final long mMillisInFuture; 
 
  /** 
   * The interval in millis that the user receives callbacks 
   */ 
  private final long mCountdownInterval; 
 
  private long mStopTimeInFuture; 
 
  /** 
   * @param millisInFuture The number of millis in the future from the call 
   *  to {@link #start()} until the countdown is done and {@link #onFinish()} 
   *  is called. 
   * @param countDownInterval The interval along the way to receive 
   *  {@link #onTick(long)} callbacks. 
   */ 
  public CountDownTimer(long millisInFuture, long countDownInterval) { 
    mMillisInFuture = millisInFuture; 
    mCountdownInterval = countDownInterval; 
  } 
 
  /** 
   * Cancel the countdown. 
   */ 
  public final void cancel() { 
    mHandler.removeMessages(MSG); 
  } 
 
  /** 
   * Start the countdown. 
   */ 
  public synchronized final CountDownTimer start() { 
    if (mMillisInFuture <= 0) { 
      onFinish(); 
      return this; 
    } 
    mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture; 
    mHandler.sendMessage(mHandler.obtainMessage(MSG)); 
    return this; 
  } 
 
 
  /** 
   * Callback fired on regular interval. 
   * @param millisUntilFinished The amount of time until finished. 
   */ 
  public abstract void onTick(long millisUntilFinished); 
 
  /** 
   * Callback fired when the time is up. 
   */ 
  public abstract void onFinish(); 
 
 
  private static final int MSG = 1; 
 
 
  // handles counting down 
  private Handler mHandler = new Handler() { 
 
    @Override 
    public void handleMessage(Message msg) { 
 
      synchronized (CountDownTimer.this) { 
        final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime(); 
 
        if (millisLeft <= 0) { 
          onFinish(); 
        } else if (millisLeft < mCountdownInterval) { 
          // no tick, just delay until done 
          sendMessageDelayed(obtainMessage(MSG), millisLeft); 
        } else { 
          long lastTickStart = SystemClock.elapsedRealtime(); 
          onTick(millisLeft); 
 
          // take into account user's onTick taking time to execute 
          long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime(); 
 
          // special case: user's onTick took more than interval to 
          // complete, skip to next interval 
          while (delay < 0) delay += mCountdownInterval; 
 
          sendMessageDelayed(obtainMessage(MSG), delay); 
        } 
      } 
    } 
  }; 
}