干货三：CountDownTimer倒计时工具类

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;    @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

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);                }            }        }    };}