概述

毫无疑问，我们先来看下官方文档中给的介绍

CountDownTimer

官方定义如下：

Schedule a countdown until a time in the future, with regular
notifications on intervals along the way.

同时官方也给出了使用的demo:

构造函数方法以及参数含义请参考官方文档，已经很明确的说明了，这里就不重复了~

Code


import android.os.Bundle;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;import com.turing.base.R;/*** 倒计时演示* <p/>* Android中有个countDownTimer类，* 从名字上就可以看出来，它的功能是记录下载时间，* 将后台线程的创建和Handler队列封装成为了一个方便的调用.* <p/>* CountDownTimer由系统提供,果断抛弃了自己以前使用Handler更新UI的做法*/
public class CountDownActivity extends AppCompatActivity {private MyCountDownTimer mc;private Button countBtn;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_count_down);countBtn = (Button) findViewById(R.id.show);// 共计30S,1S调用一次onTickmc = new MyCountDownTimer(30000, 1000);mc.start();}public void oncancel(View view) {mc.cancel();}public void restart(View view) {mc.start();}/*** 自定义倒计时类*/class MyCountDownTimer extends CountDownTimer {/*** @param millisInFuture    表示以毫秒为单位 倒计时的总数*                          <p/>*                          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*                          <p/>*                          例如: countDownInterval =1000 ;*                          表示每1000毫秒调用一次onTick()*/public MyCountDownTimer(long millisInFuture, long countDownInterval) {super(millisInFuture, countDownInterval);}@Overridepublic void onTick(long millisUntilFinished) {countBtn.setText("倒计时(" + millisUntilFinished / 1000 + ")...");}@Overridepublic void onFinish() {countBtn.setText("done");}}
}

运行图

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;/*** 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:** <pre class="prettyprint">* new CountDownTimer(30000, 1000) {**     public void onTick(long millisUntilFinished) {*         mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);*     }**     public void onFinish() {*         mTextField.setText("done!");*     }*  }.start();* </pre>** 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;/*** boolean representing if the timer was cancelled*/private boolean mCancelled = false;/*** @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 synchronized final void cancel() {mCancelled = true;mHandler.removeMessages(MSG);}/*** Start the countdown.*/public synchronized final CountDownTimer start() {mCancelled = false;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 downprivate Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {synchronized (CountDownTimer.this) {if (mCancelled) {return;}final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();if (millisLeft <= 0) {onFinish();} else if (millisLeft < mCountdownInterval) {// no tick, just delay until donesendMessageDelayed(obtainMessage(MSG), millisLeft);} else {long lastTickStart = SystemClock.elapsedRealtime();onTick(millisLeft);// take into account user's onTick taking time to executelong delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime();// special case: user's onTick took more than interval to// complete, skip to next intervalwhile (delay < 0) delay += mCountdownInterval;sendMessageDelayed(obtainMessage(MSG), delay);}}}};
}

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干货三：CountDownTimer倒计时工具类

概述

Code

运行图

CountDownTimer源码

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