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百度如何建网站,徐州百度搜索网站排名,在淘宝介绍里边怎么做网站链接,企业oa系统哪个好（一）介绍 官方文档。CountDownTimer是一个倒计时的类，还可以指定时间间隔定期通知，举个栗子，比如说你倒计时是100秒的，可以指定每20秒通知一次，这样开始的时候会回调一次，20秒时会回…

（一）介绍

官方文档。CountDownTimer是一个倒计时的类，还可以指定时间间隔定期通知，举个栗子，比如说你倒计时是100秒的，可以指定每20秒通知一次，这样开始的时候会回调一次，20秒时会回调一次，40秒时会回调一次…，200秒时的回调和时间间隔的回调不同方法的。

（二）使用

CountDownTimer只有一个构造，

/*** @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;}
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从方法的注释中可以看出，第一个参数是总的倒计时时间，第二个参数是定期的回调时间。

使用的时候：

new CountDownTimer(10000, 2000) {@Overridepublic void onTick(long millisUntilFinished) {Log.v("CountDownTimerTest", "onTick millisUntilFinished = " + millisUntilFinished);}@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}
}.start();
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onTick()方法是定期间隔回调的方法，onFinish()就是结束时回调的方法了。

"![运行结果截图](https://img-blog.csdn.net/20170305143654931?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvY2VraWFzb28=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)<br/” title=”“>
可以看出在9970毫秒的时候回调了一次onTick()方法，因为消息传递会消耗一点时间，使用传过来时是9976毫秒，后面的也是，这里执行了onTick()方法4次，那剩下2秒的时候不应该还要执行一次么？怎么3964后就不执行onTick()方法了？原因是3964毫秒再经过2秒就剩下1900多毫秒，比2秒小，使用不执行onTick()方法。

CountDownTimer的核心代码

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);long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime();while (delay < 0) delay += mCountdownInterval;sendMessageDelayed(obtainMessage(MSG), delay);
}
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如果倒计时后不让它执行了也可以取消倒计时，调用CountDownTimer的cancel()方法就可以取消倒计时了。

（三）封装

有时候我们并不关心onTick()，只需要关心onFinish()方法的执行，我们可以封装个工具类，把这两个功能分开，想单独用时就单独用，想合起来用时就合起来用。

package com.ce.countdowntimertest.utils;
import android.os.CountDownTimer;
/*** 倒计时工具类*/
public class CountDownTimerUtils {/*** 倒计时结束的回调接口*/public interface FinishDelegate {void onFinish();}/*** 定期回调的接口*/public interface TickDelegate {void onTick(long pMillisUntilFinished);}private final static long ONE_SECOND = 1000;/*** 总倒计时时间*/private long mMillisInFuture = 0;/*** 定期回调的时间 必须大于0 否则会出现ANR*/private long mCountDownInterval;/*** 倒计时结束的回调*/private FinishDelegate mFinishDelegate;/*** 定期回调*/private TickDelegate mTickDelegate;private MyCountDownTimer mCountDownTimer;/*** 获取 CountDownTimerUtils* @return CountDownTimerUtils*/public static CountDownTimerUtils getCountDownTimer() {return new CountDownTimerUtils();}/*** 设置定期回调的时间 调用{@link #setTickDelegate(TickDelegate)}* @param pCountDownInterval 定期回调的时间 必须大于0* @return CountDownTimerUtils*/public CountDownTimerUtils setCountDownInterval(long pCountDownInterval) {this.mCountDownInterval=pCountDownInterval;return this;}/*** 设置倒计时结束的回调* @param pFinishDelegate 倒计时结束的回调接口* @return CountDownTimerUtils*/public CountDownTimerUtils setFinishDelegate(FinishDelegate pFinishDelegate) {this.mFinishDelegate=pFinishDelegate;return this;}/*** 设置总倒计时时间* @param pMillisInFuture 总倒计时时间* @return CountDownTimerUtils*/public CountDownTimerUtils setMillisInFuture(long pMillisInFuture) {this.mMillisInFuture=pMillisInFuture;return this;}/*** 设置定期回调* @param pTickDelegate 定期回调接口* @return CountDownTimerUtils*/public CountDownTimerUtils setTickDelegate(TickDelegate pTickDelegate) {this.mTickDelegate=pTickDelegate;return this;}public void create() {if (mCountDownTimer != null) {mCountDownTimer.cancel();mCountDownTimer = null;}if (mCountDownInterval <= 0) {mCountDownInterval = mMillisInFuture + ONE_SECOND;}mCountDownTimer = new MyCountDownTimer(mMillisInFuture, mCountDownInterval);mCountDownTimer.setTickDelegate(mTickDelegate);mCountDownTimer.setFinishDelegate(mFinishDelegate);}/*** 开始倒计时*/public void start() {if (mCountDownTimer == null) {create();}mCountDownTimer.start();}/*** 取消倒计时*/public void cancel() {if (mCountDownTimer != null) {mCountDownTimer.cancel();}}private static class MyCountDownTimer extends CountDownTimer {private FinishDelegate mFinishDelegate;private TickDelegate mTickDelegate;/*** @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 MyCountDownTimer(long millisInFuture, long countDownInterval) {super(millisInFuture, countDownInterval);}@Overridepublic void onTick(long millisUntilFinished) {if (mTickDelegate != null) {mTickDelegate.onTick(millisUntilFinished);}}@Overridepublic void onFinish() {if (mFinishDelegate != null) {mFinishDelegate.onFinish();}}void setFinishDelegate(FinishDelegate pFinishDelegate) {this.mFinishDelegate=pFinishDelegate;}void setTickDelegate(TickDelegate pTickDelegate) {this.mTickDelegate=pTickDelegate;}}
}
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使用也简单,用getCountDownTimer()方法获取实例；setMillisInFuture()方法是设置总倒计时时间；setFinishDelegate()方法是设置倒计时完成的回调；setCountDownInterval()方法是设置定期回调的时间间隔,但值要大于0，不然会出现ANR的，因为不停的回调会导致Looper消息处理不过来；setTickDelegate()方法是设置定期回调的。
只需要最终倒计时的使用：

Log.v("CountDownTimerTest", "Start");CountDownTimerUtils.getCountDownTimer().setMillisInFuture(5000).setFinishDelegate(new CountDownTimerUtils.FinishDelegate() {@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}}).start();
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运行结果截图

也可以只要定期的间隔回调，不过要设置设置下总倒计时时间：

Log.v("CountDownTimerTest", "Start");CountDownTimerUtils.getCountDownTimer().setMillisInFuture(10000).setCountDownInterval(2000).setTickDelegate(new CountDownTimerUtils.TickDelegate() {@Overridepublic void onTick(long pMillisUntilFinished) {Log.v("CountDownTimerTest", "pMillisUntilFinished = " + pMillisUntilFinished);}}).start();
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运行结果截图

当然也可以两个都有：

Log.v("CountDownTimerTest", "Start");CountDownTimerUtils.getCountDownTimer().setMillisInFuture(10000).setCountDownInterval(2000).setTickDelegate(new CountDownTimerUtils.TickDelegate() {@Overridepublic void onTick(long pMillisUntilFinished) {Log.v("CountDownTimerTest", "pMillisUntilFinished = " + pMillisUntilFinished);}}).setFinishDelegate(new CountDownTimerUtils.FinishDelegate() {@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}}).start();
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运行结果截图

（四）改进

虽然CountDownTimer很好用，但有个缺点，就是只能在主线程中运行，如果在子线程中运行就会报错，

new Thread(new Runnable() {@Overridepublic void run() {Log.v("CountDownTimerTest", "SubThread Start");new android.os.CountDownTimer(10000, 2000) {@Overridepublic void onTick(long millisUntilFinished) {Log.v("CountDownTimerTest", "onTick millisUntilFinished = " + millisUntilFinished);}@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}}.start();}}).start();
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运行结果截图

原因是在主线程中Handler的Looper Android系统已经在framework层帮我们prepare(prepareMainLooper())过了，但在我们这个子线程没有Looper，那怎么办？我们可以借助HandlerThread完成，新建个自己的CountDownTimer类，把Android的CountDownTimer的源代码复制到我们新建的CountDownTimer类中，修改下包名，就不要用Android的CountDownTimer这个类的了，改造如下：

package com.ce.countdowntimertest.common;/** 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.*/import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.os.SystemClock;/**** Created by CE** 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;if (!isMainThread()) {mHandlerThread = new HandlerThread("CountDownTimerThread");mHandlerThread.start();mHandler = new Handler(mHandlerThread.getLooper(), mCallback);} else {mHandler = new Handler(mCallback);}}/*** 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;}private boolean isMainThread() {return Looper.getMainLooper().getThread().equals(Thread.currentThread());}/*** 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 android.os.Handler mHandler = new android.os.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);}}}};*/private HandlerThread mHandlerThread;private Handler mHandler;private Handler.Callback mCallback = new Handler.Callback() {@Overridepublic boolean handleMessage(Message msg) {synchronized (CountDownTimer.this) {if (mCancelled) {return true;}final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();if (millisLeft <= 0) {onFinish();if (mHandlerThread != null) mHandlerThread.quit();} else if (millisLeft < mCountdownInterval) {// no tick, just delay until donemHandler.sendMessageDelayed(mHandler.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;mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG), delay);}}return false;}};
}
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如果是主线程就不用管了，如果是子线程我们就把HandlerThread的getLooper()拿出来给Handler。这里我用的是Handler.Callback来进行对消息处理的。现在我们把刚才在子线程中运行的CountDownTimer类改成我们自己定义的CountDownTimer类在运行一下：

new Thread(new Runnable() {@Overridepublic void run() {Log.v("CountDownTimerTest", "SubThread Start");new com.ce.countdowntimertest.common.CountDownTimer(10000, 2000) {@Overridepublic void onTick(long millisUntilFinished) {Log.v("CountDownTimerTest", "onTick millisUntilFinished = " + millisUntilFinished);}@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}}.start();}
}).start();
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运行结果截图

可以运行了，当然在主线程也是正常的：

Log.v("CountDownTimerTest", "Start");new com.ce.countdowntimertest.common.CountDownTimer(10000, 2000) {@Overridepublic void onTick(long millisUntilFinished) {Log.v("CountDownTimerTest", "onTick millisUntilFinished = " + millisUntilFinished);}@Overridepublic void onFinish() {Log.v("CountDownTimerTest", "onFinish");}}.start();
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运行结果截图

如果在CountDownTimerUtils类里想用这个改进的CountDownTimer，改下CountDownTimer的包名就可以运行。

源码地址

                    <link rel="stylesheet" href="https://csdnimg.cn/release/phoenix/production/markdown_views-68a8aad09e.css">

转自: https://blog.csdn.net/cekiasoo/article/details/60467143
http://www.jmfq.cn/news/5274271.html

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