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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.os;
     18 
     19 import android.util.Log;
     20 
     21 /**
     22  * Schedule a countdown until a time in the future, with
     23  * regular notifications on intervals along the way.
     24  *
     25  * Example of showing a 30 second countdown in a text field:
     26  *
     27  * <pre class="prettyprint">
     28  * new CountDownTimer(30000, 1000) {
     29  *
     30  *     public void onTick(long millisUntilFinished) {
     31  *         mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
     32  *     }
     33  *
     34  *     public void onFinish() {
     35  *         mTextField.setText("done!");
     36  *     }
     37  *  }.start();
     38  * </pre>
     39  *
     40  * The calls to {@link #onTick(long)} are synchronized to this object so that
     41  * one call to {@link #onTick(long)} won't ever occur before the previous
     42  * callback is complete.  This is only relevant when the implementation of
     43  * {@link #onTick(long)} takes an amount of time to execute that is significant
     44  * compared to the countdown interval.
     45  */
     46 public abstract class CountDownTimer {
     47 
     48     /**
     49      * Millis since epoch when alarm should stop.
     50      */
     51     private final long mMillisInFuture;
     52 
     53     /**
     54      * The interval in millis that the user receives callbacks
     55      */
     56     private final long mCountdownInterval;
     57 
     58     private long mStopTimeInFuture;
     59 
     60     /**
     61      * @param millisInFuture The number of millis in the future from the call
     62      *   to {@link #start()} until the countdown is done and {@link #onFinish()}
     63      *   is called.
     64      * @param countDownInterval The interval along the way to receive
     65      *   {@link #onTick(long)} callbacks.
     66      */
     67     public CountDownTimer(long millisInFuture, long countDownInterval) {
     68         mMillisInFuture = millisInFuture;
     69         mCountdownInterval = countDownInterval;
     70     }
     71 
     72     /**
     73      * Cancel the countdown.
     74      */
     75     public final void cancel() {
     76         mHandler.removeMessages(MSG);
     77     }
     78 
     79     /**
     80      * Start the countdown.
     81      */
     82     public synchronized final CountDownTimer start() {
     83         if (mMillisInFuture <= 0) {
     84             onFinish();
     85             return this;
     86         }
     87         mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;
     88         mHandler.sendMessage(mHandler.obtainMessage(MSG));
     89         return this;
     90     }
     91 
     92 
     93     /**
     94      * Callback fired on regular interval.
     95      * @param millisUntilFinished The amount of time until finished.
     96      */
     97     public abstract void onTick(long millisUntilFinished);
     98 
     99     /**
    100      * Callback fired when the time is up.
    101      */
    102     public abstract void onFinish();
    103 
    104 
    105     private static final int MSG = 1;
    106 
    107 
    108     // handles counting down
    109     private Handler mHandler = new Handler() {
    110 
    111         @Override
    112         public void handleMessage(Message msg) {
    113 
    114             synchronized (CountDownTimer.this) {
    115                 final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();
    116 
    117                 if (millisLeft <= 0) {
    118                     onFinish();
    119                 } else if (millisLeft < mCountdownInterval) {
    120                     // no tick, just delay until done
    121                     sendMessageDelayed(obtainMessage(MSG), millisLeft);
    122                 } else {
    123                     long lastTickStart = SystemClock.elapsedRealtime();
    124                     onTick(millisLeft);
    125 
    126                     // take into account user's onTick taking time to execute
    127                     long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime();
    128 
    129                     // special case: user's onTick took more than interval to
    130                     // complete, skip to next interval
    131                     while (delay < 0) delay += mCountdownInterval;
    132 
    133                     sendMessageDelayed(obtainMessage(MSG), delay);
    134                 }
    135             }
    136         }
    137     };
    138 }
    139