Android Notification如何实现动态显示通话时间

....省略部分代码
    //震动时长，这里为不振动
    private static final long[] IN_CALL_VIBRATE_PATTERN_NULL = new long[] {0, 0, 0};
    //线程隔多久执行一次已ms为单位，这里为1S
    private static final long CALL_TIME_UPDATE_INTERVAL_MS = 1000;

    //我们需要获取一些全局的变量，已到达不停的创建notification并更新同一个notification的UI
    private CallTimer mCallTimer;
    private Notification.Builder mCopyBuilder;
    private int  mCopyCallState;
    private ContactCacheEntry mCopyContactInfo;
    private int mCopyNotificationType; //当前notification的ID,通过这个ID我们可以一直更新同一个notification并且只会弹出一次
    private Bitmap mCopyLargeIcon;

    public StatusBarNotifier(Context context, ContactInfoCache contactInfoCache) {
        .......省略部分代码
        //StatusBarNotifier初始化的时候就创建CallTimer对象，用来计算时间和更新UI
        mCallTimer = new CallTimer(new Runnable() {
            @Override
            public void run() {
                updateCallTime(); //更新UI的函数
            }
        });
    }

    @Override
    public void onStateChange(InCallState oldState, InCallState newState, CallList callList) {
        if (callList.getActiveCall() == null || callList.getActiveCall().getState() != Call.State.ACTIVE){
            //当通话结束时需要取消计算时间的线程
            mCallTimer.cancel();
        }
    }

    //系统构建notification的方法
    private void buildAndSendNotification(Call originalCall, ContactCacheEntry contactInfo) {
        ....省略部分代码
        else if (callState == Call.State.ACTIVE && !mIsCallUiShown) {
            //保存一个公共的变量到全部变量里面，方便后面构造新的notification并刷新
            copyInfoFromHeadsUpView(builder, callState, contactInfo, notificationType, largeIcon);
            //下面是计算显示的时间
            final long callStart = call.getConnectTimeMillis();
            final long duration = System.currentTimeMillis() - callStart;
            //创建一个HeadsUpView显示在notification上面
            RemoteViews inCall = createInCallHeadsUpView(duration / 1000, largeIcon);
            builder.setContent(inCall);
            builder.setCustomHeadsUpContentView(inCall);
            //系统原生的方法最后notify通知
            fireNotification(builder, callState, contactInfo, notificationType);
            //开始我们的计时线程
            mCallTimer.start(CALL_TIME_UPDATE_INTERVAL_MS);
        }

        .....省略部分代码
    }

    private RemoteViews createInCallHeadsUpView(Long callDuration, Bitmap contactAvatar) {
        RemoteViews headsUpView = new RemoteViews(mContext.getPackageName(), R.layout.in_call_headsup);
        if (null != contactAvatar) {
            headsUpView.setImageViewBitmap(R.id.in_call_hu_avatar, contactAvatar);
        }
        //格式化时间
        String callTimeElapsed = DateUtils.formatElapsedTime(callDuration);
        headsUpView.setTextViewText(R.id.in_call_hu_elapsedTime, callTimeElapsed);
        return headsUpView;
    }

    /*according the mCallTimer to update time data*/
    public void updateCallTime() {
        Call call = CallList.getInstance().getActiveCall();
        final long callStart = call.getConnectTimeMillis();
        final long duration = System.currentTimeMillis() - callStart;
        RemoteViews inCall = createInCallHeadsUpView(duration / 1000, mCopyLargeIcon);
        mCopyBuilder.setContent(inCall);
        mCopyBuilder.setCustomHeadsUpContentView(inCall);
        Notification notification = mCopyBuilder.build();
        notification.vibrate = IN_CALL_VIBRATE_PATTERN_NULL;
        mNotificationManager.notify(mCopyNotificationType, notification);

    }

    /*Change local variables  to global variables*/
    private void copyInfoFromHeadsUpView(Notification.Builder builder, int callState, ContactCacheEntry contactInfo,
                          int notificationType, Bitmap largeIcon){
        mCopyBuilder = builder;
        mCopyCallState = callState;
        mCopyContactInfo = contactInfo;
        mCopyNotificationType = notificationType;
        mCopyLargeIcon = largeIcon;
    }

........省略部分代码

package com.android.incallui;

import com.google.common.base.Preconditions;

import android.os.Handler;
import android.os.SystemClock;

/**
 * Helper class used to keep track of events requiring regular intervals.
 */
public class CallTimer extends Handler {
    private Runnable mInternalCallback;
    private Runnable mCallback;
    private long mLastReportedTime;
    private long mInterval;
    private boolean mRunning;

    public CallTimer(Runnable callback) {
        Preconditions.checkNotNull(callback);

        mInterval = 0;
        mLastReportedTime = 0;
        mRunning = false;
        mCallback = callback;
        mInternalCallback = new CallTimerCallback();
    }

    public boolean start(long interval) {
        if (interval <= 0) {
            return false;
        }

        // cancel any previous timer
        cancel();

        mInterval = interval;
        mLastReportedTime = SystemClock.uptimeMillis();

        mRunning = true;
        periodicUpdateTimer();

        return true;
    }

    public void cancel() {
        removeCallbacks(mInternalCallback);
        mRunning = false;
    }

    private void periodicUpdateTimer() {
        if (!mRunning) {
            return;
        }

        final long now = SystemClock.uptimeMillis();
        long nextReport = mLastReportedTime + mInterval;
        while (now >= nextReport) {
            nextReport += mInterval;
        }

        postAtTime(mInternalCallback, nextReport);
        mLastReportedTime = nextReport;

        // Run the callback
        mCallback.run();
    }

    private class CallTimerCallback implements Runnable {
        @Override
        public void run() {
            periodicUpdateTimer();
        }
    }
}