android 源码——packages/apps/Music学习二

长按"上一首"、"下一首"按钮实现歌曲快退、快进功能，代码如下

重写按钮ImageButton，RepeatingImageButton.java

/**
 * A button that will repeatedly call a 'listener' method
 * as long as the button is pressed.
 */
public class RepeatingImageButton extends ImageButton {

    private long mStartTime;
    private int mRepeatCount;
    private RepeatListener mListener;
    private long mInterval = 500;
    
    public RepeatingImageButton(Context context) {
        this(context, null);
    }

    public RepeatingImageButton(Context context, AttributeSet attrs) {
        this(context, attrs, android.R.attr.imageButtonStyle);
    }

    public RepeatingImageButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        setFocusable(true);
        setLongClickable(true);
    }
    
    /**
     * Sets the listener to be called while the button is pressed and
     * the interval in milliseconds with which it will be called.
     * @param l The listener that will be called
     * @param interval The interval in milliseconds for calls 
     */
    public void setRepeatListener(RepeatListener l, long interval) {
        mListener = l;
        mInterval = interval;
    }
    
    @Override
    public boolean performLongClick() {
        mStartTime = SystemClock.elapsedRealtime();
        mRepeatCount = 0;
        post(mRepeater);
        return true;
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_UP) {
            // remove the repeater, but call the hook one more time
            removeCallbacks(mRepeater);
            if (mStartTime != 0) {
                doRepeat(true);
                mStartTime = 0;
            }
        }
        return super.onTouchEvent(event);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_CENTER:
            case KeyEvent.KEYCODE_ENTER:
                // need to call super to make long press work, but return
                // true so that the application doesn't get the down event.
                super.onKeyDown(keyCode, event);
                return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        switch (keyCode) {
        case KeyEvent.KEYCODE_DPAD_CENTER:
        case KeyEvent.KEYCODE_ENTER:
            // remove the repeater, but call the hook one more time
            removeCallbacks(mRepeater);
            if (mStartTime != 0) {
                doRepeat(true);
                mStartTime = 0;
            }
        }
        return super.onKeyUp(keyCode, event);
    }
    
    private Runnable mRepeater = new Runnable() {
        public void run() {
            doRepeat(false);
            if (isPressed()) {
                postDelayed(this, mInterval);
            }
        }
    };

    private  void doRepeat(boolean last) {
        long now = SystemClock.elapsedRealtime();
        if (mListener != null) {
            mListener.onRepeat(this, now - mStartTime, last ? -1 : mRepeatCount++);
        }
    }
    
    public interface RepeatListener {
        /**
         * This method will be called repeatedly at roughly the interval
         * specified in setRepeatListener(), for as long as the button
         * is pressed.
         * @param v The button as a View.
         * @param duration The number of milliseconds the button has been pressed so far.
         * @param repeatcount The number of previous calls in this sequence.
         * If this is going to be the last call in this sequence (i.e. the user
         * just stopped pressing the button), the value will be -1.  
         */
        void onRepeat(View v, long duration, int repeatcount);
    }
}

MediaPlaybackActivity.java中的代码如下：

        mNextButton = (RepeatingImageButton) findViewById(R.id.next);
        mNextButton.setOnClickListener(mNextListener);
        mNextButton.setRepeatListener(mFfwdListener, 260);

    private RepeatingImageButton.RepeatListener mFfwdListener =
        new RepeatingImageButton.RepeatListener() {
        public void onRepeat(View v, long howlong, int repcnt) {
            scanForward(repcnt, howlong);
        }
    };

    private void scanForward(int repcnt, long delta) {
        if(mService == null) return;
        try {
            if(repcnt == 0) {
                mStartSeekPos = mService.position();
                mLastSeekEventTime = 0;
                mSeeking = false;
            } else {
                mSeeking = true;
                if (delta < 5000) {
                    // seek at 10x speed for the first 5 seconds
                    delta = delta * 10; 
                } else {
                    // seek at 40x after that
                    delta = 50000 + (delta - 5000) * 40;
                }
                long newpos = mStartSeekPos + delta;
                long duration = mService.duration();
                if (newpos >= duration) {
                    // move to next track
                    mService.next();
                    mStartSeekPos -= duration; // is OK to go negative
                    newpos -= duration;
                }
                if (((delta - mLastSeekEventTime) > 250) || repcnt < 0){
                    mService.seek(newpos);
                    mLastSeekEventTime = delta;
                }
                if (repcnt >= 0) {
                    mPosOverride = newpos;
                } else {
                    mPosOverride = -1;
                }
                refreshNow();
            }
        } catch (RemoteException ex) {
        }
    }

        mPrevButton = (RepeatingImageButton) findViewById(R.id.prev);
        mPrevButton.setOnClickListener(mPrevListener);
        mPrevButton.setRepeatListener(mRewListener, 260);

    private RepeatingImageButton.RepeatListener mRewListener =
        new RepeatingImageButton.RepeatListener() {
        public void onRepeat(View v, long howlong, int repcnt) {
            scanBackward(repcnt, howlong);
        }
    };

    private void scanBackward(int repcnt, long delta) {
        if(mService == null) return;
        try {
            if(repcnt == 0) {
                mStartSeekPos = mService.position();
                mLastSeekEventTime = 0;
                mSeeking = false;
            } else {
                mSeeking = true;
                if (delta < 5000) {
                    // seek at 10x speed for the first 5 seconds
                    delta = delta * 10; 
                } else {
                    // seek at 40x after that
                    delta = 50000 + (delta - 5000) * 40;
                }
                long newpos = mStartSeekPos - delta;
                if (newpos < 0) {
                    // move to previous track
                    mService.prev();
                    long duration = mService.duration();
                    mStartSeekPos += duration;
                    newpos += duration;
                }
                if (((delta - mLastSeekEventTime) > 250) || repcnt < 0){
                    mService.seek(newpos);
                    mLastSeekEventTime = delta;
                }
                if (repcnt >= 0) {
                    mPosOverride = newpos;
                } else {
                    mPosOverride = -1;
                }
                refreshNow();
            }
        } catch (RemoteException ex) {
        }
    }