使用CountDownTimer类轻松实现倒计时功能

CountDownTimer由系统提供
查资料的时候发现了CountDownTimer这个类之后果断抛弃了以前的倒计时做法
功能:
30秒倒计时每次间隔1秒
参数:
mc.start（）;方法开始
mc.cancel（）;方法结束
new MyCountDownTimer（30000, 1000）; 第一个参数表示总的时间为30000毫秒,间隔1000毫秒
直接上代码:

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！ //┃   ┗━━━┓ //┃       ┣┓ //┃       ┏┛ //┗┓┓┏━┳┓┏┛ // ┃┫┫ ┃┫┫ // ┗┻┛ ┗┻┛

布局:

<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>

附:
CountDownTimer源码:

/** 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）; } } } }; }