倒计时器源码

最新推荐文章于 2023-10-23 14:16:55 发布

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最新推荐文章于 2023-10-23 14:16:55 发布

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本文深入探讨了Android OS中的CountDownTimer类，详细解释了其构造、启动、取消和核心方法，如onTick和onFinish。通过实例演示如何在Android应用中使用此类来实现计时功能。

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package android.os;

import android.util.Log;

public abstract class CountDownTimer {
private final long mMillisInFuture;
private final long mCountdownInterval;
private long mStopTimeInFuture;

public CountDownTimer(long millisInFuture, long countDownInterval) {
mMillisInFuture = millisInFuture;
mCountdownInterval = countDownInterval;
}

public final void cancel() {
mHandler.removeMessages(MSG);
}

public synchronized final CountDownTimer start() {
if (mMillisInFuture <= 0) {
onFinish();
return this;
}

mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;
mHandler.sendMessage(mHandler.obtainMessage(MSG));
return this;
}
public abstract void onTick(long millisUntilFinished);
public abstract void onFinish();
private static final int MSG = 1;
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) {
sendMessageDelayed(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);
}
}

}

};
}