使用介紹
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開發(fā)中經(jīng)常會(huì)遇到一些和倒計(jì)時(shí)有關(guān)的場(chǎng)景，比如發(fā)送驗(yàn)證碼的按鈕，會(huì)在點(diǎn)擊發(fā)送后，顯示倒計(jì)時(shí)間，倒計(jì)時(shí)結(jié)束后才能夠刷新按鈕，再次允許點(diǎn)擊。為了不阻塞軟件的運(yùn)行，又要實(shí)時(shí)刷新界面，我們通常會(huì)用到 Handler 或者 AsyncTask 等技術(shù)，自己寫邏輯實(shí)現(xiàn)。其實(shí) Android 中已經(jīng)封裝好了一套 CountDownTimer 來實(shí)現(xiàn)這個(gè)功能需求。
CountDownTimer(long millisInFuture, long countDownInterval)
CountDownTimer的兩個(gè)參數(shù)分別表示倒計(jì)時(shí)的總時(shí)間 millisInFuture和間隔時(shí)間 countDownInterval。
具體的調(diào)用如下：
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重慶分公司
TextView vertifyBtn;
CountDownTimer timer = new CountDownTimer(60000, 1000) {
@Override
public void onTick(long millisUntilFinished) {
vertifyBtn.setText((millisUntilFinished / 1000) + " second");
}
@Override
public void onFinish() {
vertifyBtn.setEnabled(true);
vertifyBtn.setText("Send");
}
};
timer.start();
上面的調(diào)用舉例表示總計(jì) 60 秒，每 1 秒都會(huì)執(zhí)行一次 onTick 方法，其參數(shù) millisUntilFinished 表示倒計(jì)時(shí)剩余時(shí)間毫秒數(shù)，最后倒計(jì)時(shí)結(jié)束執(zhí)行 onFinish 方法。
實(shí)現(xiàn)原理
下面是 CountDownTimer 的源碼，代碼非常少，很好理解。從源代碼中可以看出，其實(shí) CountDownTimer 也是利用 Handler 的消息處理機(jī)制來實(shí)現(xiàn)效果的。初始化設(shè)定好起始和終止時(shí)間后，每隔一定的間隔時(shí)間通過 Handler 給主線程發(fā)送消息，然后再在消息處理中回調(diào)方法。好好利用官方封裝好的工具類，可以避免我們重復(fù)的造輪子，當(dāng)然了解輪子的原理就更好了！
package android.os;
public abstract class CountDownTimer {
private final long mMillisInFuture;
private final long mCountdownInterval;
private long mStopTimeInFuture;
private boolean mCancelled = false;
public CountDownTimer(long millisInFuture, long countDownInterval) {
mMillisInFuture = millisInFuture;
mCountdownInterval = countDownInterval;
}
public synchronized final void cancel() {
mCancelled = true;
mHandler.removeMessages(MSG);
}
public synchronized final CountDownTimer start() {
mCancelled = false;
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) {
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);
}
}
}
};
}
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持創(chuàng)新互聯(lián)。
