须知CountDownTimer轻松实现倒计时功能的方法

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);         }       }     }   }; }