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);
}
}
}
};
}

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