Android自动滚动轮播循环的ViewPager

来源：http://www.trinea.cn/android/auto-scroll-view-pager/

1.实现方式

没有通过ScheduledExecutorService或Timer定期执行某个任务实现，而是简单的通过handler发送消息去完成一次滚动，在完成一次滚动后发送另外一个delay的滚动消息，如此循环实现。

2.自定义ViewPager

public class AutoScrollViewPager extends ViewPager {    public static final int        DEFAULT_INTERVAL            = 1500;    public static final int        LEFT                        = 0;    public static final int        RIGHT                       = 1;    /** do nothing when sliding at the last or first item **/    public static final int        SLIDE_BORDER_MODE_NONE      = 0;    /** cycle when sliding at the last or first item **/    public static final int        SLIDE_BORDER_MODE_CYCLE     = 1;    /** deliver event to parent when sliding at the last or first item **/    public static final int        SLIDE_BORDER_MODE_TO_PARENT = 2;    /** auto scroll time in milliseconds, default is {@link #DEFAULT_INTERVAL} **/    private long                   interval                    = DEFAULT_INTERVAL;    /** auto scroll direction, default is {@link #RIGHT} **/    private int                    direction                   = RIGHT;    /** whether automatic cycle when auto scroll reaching the last or first item, default is true **/    private boolean                isCycle                     = true;    /** whether stop auto scroll when touching, default is true **/    private boolean                stopScrollWhenTouch         = true;    /** how to process when sliding at the last or first item, default is {@link #SLIDE_BORDER_MODE_NONE} **/    private int                    slideBorderMode             = SLIDE_BORDER_MODE_NONE;    /** whether animating when auto scroll at the last or first item **/    private boolean                isBorderAnimation           = true;    private Handler                handler;    private boolean                isAutoScroll                = false;    private boolean                isStopByTouch               = false;    private float                  touchX                      = 0f, downX = 0f;    private CustomDurationScroller scroller                    = null;    public static final int        SCROLL_WHAT                 = 0;    public AutoScrollViewPager(Context paramContext) {        super(paramContext);        init();    }    public AutoScrollViewPager(Context paramContext, AttributeSet paramAttributeSet) {        super(paramContext, paramAttributeSet);        init();    }    private void init() {        handler = new MyHandler();        setViewPagerScroller();    }    /**     * start auto scroll, first scroll delay time is {@link #getInterval()}     */    public void startAutoScroll() {        isAutoScroll = true;        sendScrollMessage(interval);    }    /**     * start auto scroll     *     * @param delayTimeInMills first scroll delay time     */    public void startAutoScroll(int delayTimeInMills) {        isAutoScroll = true;        sendScrollMessage(delayTimeInMills);    }    /**     * stop auto scroll     */    public void stopAutoScroll() {        isAutoScroll = false;        handler.removeMessages(SCROLL_WHAT);    }    /**     * set the factor by which the duration of sliding animation will change     */    public void setScrollDurationFactor(double scrollFactor) {        scroller.setScrollDurationFactor(scrollFactor);    }    private void sendScrollMessage(long delayTimeInMills) {        /** remove messages before, keeps one message is running at most **/        handler.removeMessages(SCROLL_WHAT);        handler.sendEmptyMessageDelayed(SCROLL_WHAT, delayTimeInMills);    }    /**     * set ViewPager scroller to change animation duration when sliding     */    private void setViewPagerScroller() {        try {            Field scrollerField = ViewPager.class.getDeclaredField("mScroller");            scrollerField.setAccessible(true);            Field interpolatorField = ViewPager.class.getDeclaredField("sInterpolator");            interpolatorField.setAccessible(true);            scroller = new CustomDurationScroller(getContext(), (Interpolator)interpolatorField.get(null));            scrollerField.set(this, scroller);        } catch (Exception e) {            e.printStackTrace();        }    }    /**     * scroll only once     */    public void scrollOnce() {        PagerAdapter adapter = getAdapter();        int currentItem = getCurrentItem();        int totalCount;        if (adapter == null || (totalCount = adapter.getCount()) <= 1) {            return;        }        int nextItem = (direction == LEFT) ? --currentItem : ++currentItem;        if (nextItem < 0) {            if (isCycle) {                setCurrentItem(totalCount - 1, isBorderAnimation);            }        } else if (nextItem == totalCount) {            if (isCycle) {                setCurrentItem(0, isBorderAnimation);            }        } else {            setCurrentItem(nextItem, true);        }    }    /**     *      * if stopScrollWhenTouch is true     * if event is down, stop auto scroll.
     * if event is up, start auto scroll again.
     * 
     */    @Override    public boolean onTouchEvent(MotionEvent ev) {        if (stopScrollWhenTouch) {            if (ev.getAction() == MotionEvent.ACTION_DOWN && isAutoScroll) {                isStopByTouch = true;                stopAutoScroll();            } else if (ev.getAction() == MotionEvent.ACTION_UP && isStopByTouch) {                startAutoScroll();            }        }        if (slideBorderMode == SLIDE_BORDER_MODE_TO_PARENT || slideBorderMode == SLIDE_BORDER_MODE_CYCLE) {            touchX = ev.getX();            if (ev.getAction() == MotionEvent.ACTION_DOWN) {                downX = touchX;            }            int currentItem = getCurrentItem();            PagerAdapter adapter = getAdapter();            int pageCount = adapter == null ? 0 : adapter.getCount();            /**             * current index is first one and slide to right or current index is last one and slide to left.
             * if slide border mode is to parent, then requestDisallowInterceptTouchEvent false.
             * else scroll to last one when current item is first one, scroll to first one when current item is last             * one.             */            if ((currentItem == 0 && downX <= touchX) || (currentItem == pageCount - 1 && downX >= touchX)) {                if (slideBorderMode == SLIDE_BORDER_MODE_TO_PARENT) {                    getParent().requestDisallowInterceptTouchEvent(false);                } else {                    if (pageCount > 1) {                        setCurrentItem(pageCount - currentItem - 1, isBorderAnimation);                    }                    getParent().requestDisallowInterceptTouchEvent(true);                }                return super.onTouchEvent(ev);            }        }        getParent().requestDisallowInterceptTouchEvent(true);        return super.onTouchEvent(ev);    }    private class MyHandler extends Handler {        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            switch (msg.what) {                case SCROLL_WHAT:                    scrollOnce();                    sendScrollMessage(interval);                default:                    break;            }        }    }    /**     * get auto scroll time in milliseconds, default is {@link #DEFAULT_INTERVAL}     *     * @return the interval     */    public long getInterval() {        return interval;    }    /**     * set auto scroll time in milliseconds, default is {@link #DEFAULT_INTERVAL}     *     * @param interval the interval to set     */    public void setInterval(long interval) {        this.interval = interval;    }    /**     * get auto scroll direction     *     * @return {@link #LEFT} or {@link #RIGHT}, default is {@link #RIGHT}     */    public int getDirection() {        return (direction == LEFT) ? LEFT : RIGHT;    }    /**     * set auto scroll direction     *     * @param direction {@link #LEFT} or {@link #RIGHT}, default is {@link #RIGHT}     */    public void setDirection(int direction) {        this.direction = direction;    }    /**     * whether automatic cycle when auto scroll reaching the last or first item, default is true     *     * @return the isCycle     */    public boolean isCycle() {        return isCycle;    }    /**     * set whether automatic cycle when auto scroll reaching the last or first item, default is true     *     * @param isCycle the isCycle to set     */    public void setCycle(boolean isCycle) {        this.isCycle = isCycle;    }    /**     * whether stop auto scroll when touching, default is true     *     * @return the stopScrollWhenTouch     */    public boolean isStopScrollWhenTouch() {        return stopScrollWhenTouch;    }    /**     * set whether stop auto scroll when touching, default is true     *     * @param stopScrollWhenTouch     */    public void setStopScrollWhenTouch(boolean stopScrollWhenTouch) {        this.stopScrollWhenTouch = stopScrollWhenTouch;    }    /**     * get how to process when sliding at the last or first item     *     * @return the slideBorderMode {@link #SLIDE_BORDER_MODE_NONE}, {@link #SLIDE_BORDER_MODE_TO_PARENT},     *         {@link #SLIDE_BORDER_MODE_CYCLE}, default is {@link #SLIDE_BORDER_MODE_NONE}     */    public int getSlideBorderMode() {        return slideBorderMode;    }    /**     * set how to process when sliding at the last or first item     *     * @param slideBorderMode {@link #SLIDE_BORDER_MODE_NONE}, {@link #SLIDE_BORDER_MODE_TO_PARENT},     *        {@link #SLIDE_BORDER_MODE_CYCLE}, default is {@link #SLIDE_BORDER_MODE_NONE}     */    public void setSlideBorderMode(int slideBorderMode) {        this.slideBorderMode = slideBorderMode;    }    /**     * whether animating when auto scroll at the last or first item, default is true     *     * @return     */    public boolean isBorderAnimation() {        return isBorderAnimation;    }    /**     * set whether animating when auto scroll at the last or first item, default is true     *     * @param isBorderAnimation     */    public void setBorderAnimation(boolean isBorderAnimation) {        this.isBorderAnimation = isBorderAnimation;    }}

自定义ViewPager时用的Scroller

public class CustomDurationScroller extends Scroller {    private double scrollFactor = 1;    public CustomDurationScroller(Context context) {        super(context);    }    public CustomDurationScroller(Context context, Interpolator interpolator) {        super(context, interpolator);    }    /**     * Set the factor by which the duration will change     */    public void setScrollDurationFactor(double scrollFactor) {        this.scrollFactor = scrollFactor;    }    @Override    public void startScroll(int startX, int startY, int dx, int dy, int duration) {        super.startScroll(startX, startY, dx, dy, (int)(duration * scrollFactor));    }}

3.自动滚动核心代码

用户调用startAutoScroll()后发送一条滚动消息，执行完滚动后重新发送一条滚动消息

 /**     * start auto scroll, first scroll delay time is {@link #getInterval()}     */    public void startAutoScroll() {        isAutoScroll = true;        sendScrollMessage(interval);    } private void sendScrollMessage(long delayTimeInMills) {        /** remove messages before, keeps one message is running at most **/        handler.removeMessages(SCROLL_WHAT);        handler.sendEmptyMessageDelayed(SCROLL_WHAT, delayTimeInMills);    } private class MyHandler extends Handler {        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            switch (msg.what) {                case SCROLL_WHAT:                    scrollOnce();                    sendScrollMessage(interval);                default:                    break;            }        }    }

---

4.自动滚动和滑动冲突解决

 /**     *      * if stopScrollWhenTouch is true     * if event is down, stop auto scroll.
     * if event is up, start auto scroll again.
     * 
     */    @Override    public boolean onTouchEvent(MotionEvent ev) {        if (stopScrollWhenTouch) {            if (ev.getAction() == MotionEvent.ACTION_DOWN && isAutoScroll) {                isStopByTouch = true;                stopAutoScroll();            } else if (ev.getAction() == MotionEvent.ACTION_UP && isStopByTouch) {                startAutoScroll();            }        }        ......

5.滑动到边界时的处理

/** * current index is first one and slide to right or current index is last one and slide to left.
 * if slide border mode is to parent, then requestDisallowInterceptTouchEvent false.
 * else scroll to last one when current item is first one, scroll to first one when current item is last * one. */if ((currentItem == 0 && downX <= touchX) || (currentItem == pageCount - 1 && downX >= touchX)) {if (slideBorderMode == SLIDE_BORDER_MODE_TO_PARENT) {getParent().requestDisallowInterceptTouchEvent(false);} else {if (pageCount > 1) {setCurrentItem(pageCount - currentItem - 1, isBorderAnimation);}getParent().requestDisallowInterceptTouchEvent(true);}return super.onTouchEvent(ev);}
   
   
   
    至于ViewPager嵌套引起子ViewPager无法触摸问题是通过在子ViewPager的onTouchEvent中添加
                                                 Java                                                                             1                                                          getParent().requestDisallowInterceptTouchEvent(true);                           
      
     
           禁止父控件对touch event做intercept解决的。
     
    ViewPager滑动速度的设置是通过反射的方式重新设置ViewPager的Scroller，改变Scroller的startScroll的间隔时间完成的。调用setScrollDurationFactor(double)即可。
    
   
   


   
   
   
   





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