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:

干货三:CountDownTimer倒计时工具类_CountDownT

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;


@Override
protected 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onTick
mc = 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);
}

@Override
public void onTick(long millisUntilFinished) {
countBtn.setText("倒计时(" + millisUntilFinished / 1000 + ")...");
}

@Override
public void onFinish() {
countBtn.setText("done");
}
}
}

运行图

干货三:CountDownTimer倒计时工具类_CountDownT_02

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 down
private Handler mHandler = new Handler() {

@Override
public 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 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);
}
}
}
};
}