android计时器类CountDownTime的运用及扩展

最近需要一个倒数计时器，要求实现倒数计时，暂停，继续，和快进快退的功能。Android本身提供了一个CountdownTimer的类，采用Handler的方式实现，但是只提供了倒数计时的功能，对于暂停，继续，快进快退功能未提供支持，于是在CounterDownTimer的基础上重写了一个类，最终满足要求。

import android.os.Handler;
import android.os.Message;

public abstract class AdvancedCountdownTimer {

	private final long mCountdownInterval;

	private long mTotalTime;

	private long mRemainTime;

	
	public AdvancedCountdownTimer(long millisInFuture, long countDownInterval) {
		mTotalTime = millisInFuture;
		mCountdownInterval = countDownInterval;

		mRemainTime = millisInFuture;
	}

	public final void seek(int value) {
		synchronized (AdvancedCountdownTimer.this) {
			mRemainTime = ((100 - value) * mTotalTime) / 100;
		}
	}

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

	public final void resume() {
		mHandler.removeMessages(MSG_PAUSE);
		mHandler.sendMessageAtFrontOfQueue(mHandler.obtainMessage(MSG_RUN));
	}

	public final void pause() {
		mHandler.removeMessages(MSG_RUN);
		mHandler.sendMessageAtFrontOfQueue(mHandler.obtainMessage(MSG_PAUSE));
	}

	
	public synchronized final AdvancedCountdownTimer start() {
		if (mRemainTime <= 0) {
			onFinish();
			return this;
		}
		mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG_RUN),
				mCountdownInterval);
		return this;
	}

	public abstract void onTick(long millisUntilFinished, int percent);

	
	public abstract void onFinish();

	private static final int MSG_RUN = 1;
	private static final int MSG_PAUSE = 2;

	private Handler mHandler = new Handler() {

		@Override
		public void handleMessage(Message msg) {

			synchronized (AdvancedCountdownTimer.this) {
				if (msg.what == MSG_RUN) {
					mRemainTime = mRemainTime - mCountdownInterval;

					if (mRemainTime <= 0) {
						onFinish();
					} else if (mRemainTime < mCountdownInterval) {
						sendMessageDelayed(obtainMessage(MSG_RUN), mRemainTime);
					} else {

						onTick(mRemainTime, new Long(100
								* (mTotalTime - mRemainTime) / mTotalTime)
								.intValue());

					
						sendMessageDelayed(obtainMessage(MSG_RUN),
								mCountdownInterval);
					}
				} else if (msg.what == MSG_PAUSE) {

				}
			}
		}
	};
}

android自带的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:
 *
 * <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;

    /***
     * @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);
                }
            }
        }
    };
}

这个是CountDownTimer的实际运用例子：
http://gundumw100.iteye.com/admin/blogs/1057989