ViewPagerIndicator-master源码分析 3

1 TitlePageIndicator

效果图

public class TitlePageIndicator extends View implements PageIndicator {
    /**
     * Percentage indicating what percentage of the screen width away from
     * center should the underline be fully faded. A value of 0.25 means that
     * halfway between the center of the screen and an edge.
     * 指示条和透明度的变化区间值
     */
    private static final float SELECTION_FADE_PERCENTAGE = 0.25f;

    /**
     * Percentage indicating what percentage of the screen width away from
     * center should the selected text bold turn off. A value of 0.05 means
     * that 10% between the center and an edge.--中心到边界
     * 粗体的变化区间值，
     */
    private static final float BOLD_FADE_PERCENTAGE = 0.05f;
    // 枚举的典型例子
    public enum IndicatorStyle {
        None(0), Triangle(1), Underline(2);
        public final int value;
        private IndicatorStyle(int value) {
            this.value = value;
        }
        public static IndicatorStyle fromValue(int value) {
            for (IndicatorStyle style : IndicatorStyle.values()) {
                if (style.value == value) {
                    return style;
                }
            }
            return null;
        }
    }

    public enum LinePosition {
        Bottom(0), Top(1);
        public final int value;
        private LinePosition(int value) {
            this.value = value;
        }
        public static LinePosition fromValue(int value) {
            for (LinePosition position : LinePosition.values()) {
                if (position.value == value) {
                    return position;
                }
            }
            return null;
        }
    }

    private ViewPager mViewPager;
    private ViewPager.OnPageChangeListener mListener;
    private int mCurrentPage = -1;
    private float mPageOffset;
    private int mScrollState;
    private final Paint mPaintText = new Paint();
    private boolean mBoldText;
    private int mColorText;
    private int mColorSelected;
    private Path mPath = new Path();
    private final Rect mBounds = new Rect();
    private final Paint mPaintFooterLine = new Paint();
    private IndicatorStyle mFooterIndicatorStyle;
    private LinePosition mLinePosition;
    private final Paint mPaintFooterIndicator = new Paint();
    private float mFooterIndicatorHeight;
    private float mFooterIndicatorUnderlinePadding;
    private float mFooterPadding;
    private float mTitlePadding;
    private float mTopPadding;
    /** Left and right side padding for not active view titles. */
    private float mClipPadding;
    private float mFooterLineHeight;

    private static final int INVALID_POINTER = -1;

    private int mTouchSlop;
    private float mLastMotionX = -1;
    private int mActivePointerId = INVALID_POINTER;
    private boolean mIsDragging;

    public TitlePageIndicator(Context context) {
        this(context, null);
    }
    public TitlePageIndicator(Context context, AttributeSet attrs) {
        this(context, attrs, R.attr.vpiTitlePageIndicatorStyle);
    }
    public TitlePageIndicator(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        if (isInEditMode()) return;// edit mode
        //Load defaults from resources
        final Resources res = getResources();
        // 赋值略...
        mPaintText.setTextSize(textSize);
        mPaintText.setAntiAlias(true);
        // Geometry and text drawn with this style will be both filled and stroked at the same time
        mPaintFooterLine.setStyle(Paint.Style.FILL_AND_STROKE); 
        mPaintFooterLine.setStrokeWidth(mFooterLineHeight);
        mPaintFooterLine.setColor(footerColor);
        mPaintFooterIndicator.setStyle(Paint.Style.FILL_AND_STROKE);
        mPaintFooterIndicator.setColor(footerColor);

        final ViewConfiguration configuration = ViewConfiguration.get(context);
        mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (mViewPager == null) {
            return;
        }
        final int count = mViewPager.getAdapter().getCount();
        if (count == 0) {
            return;
        }
        // mCurrentPage is -1 on first start and after orientation changed. If so, retrieve the correct index from viewpager.
        if (mCurrentPage == -1 && mViewPager != null) {
            mCurrentPage = mViewPager.getCurrentItem();
        }
        //Calculate views bounds 计算所有的标题区间，重要！！！否则下面不好理解
        ArrayList<Rect> bounds = calculateAllBounds(mPaintText);
        final int boundsSize = bounds.size();

        //Make sure we're on a page that still exists
        if (mCurrentPage >= boundsSize) {
            setCurrentItem(boundsSize - 1);
            return;
        }

        final int countMinusOne = count - 1;
        final float halfWidth = getWidth() / 2f;
        final int left = getLeft();
        final float leftClip = left + mClipPadding;//左边距
        final int width = getWidth();
        int height = getHeight();
        final int right = left + width;
        final float rightClip = right - mClipPadding;

        int page = mCurrentPage;
        float offsetPercent;
        if (mPageOffset <= 0.5) {
            offsetPercent = mPageOffset;
        } else {
            page += 1; // 说明正在从中心页向右滑动，中心页=mCurrentPage+1
            // 或者向左滑动了超过了页面的一半距离
            offsetPercent = 1 - mPageOffset;
        }
        final boolean currentSelected = (offsetPercent <= SELECTION_FADE_PERCENTAGE);//透明效果
        final boolean currentBold = (offsetPercent <= BOLD_FADE_PERCENTAGE);//黑体
        final float selectedPercent = (SELECTION_FADE_PERCENTAGE - offsetPercent) / SELECTION_FADE_PERCENTAGE;//百分比

        //Verify if the current view must be clipped to the screen
        Rect curPageBound = bounds.get(mCurrentPage);
        float curPageWidth = curPageBound.right - curPageBound.left;
        if (curPageBound.left < leftClip) {
            //Try to clip to the screen (left side)
            clipViewOnTheLeft(curPageBound, curPageWidth, left);
        }
        if (curPageBound.right > rightClip) {
            //Try to clip to the screen (right side)
            clipViewOnTheRight(curPageBound, curPageWidth, right);
        }
        //Left views starting from the current position 裁剪左边view
        if (mCurrentPage > 0) {
            for (int i = mCurrentPage - 1; i >= 0; i--) {
                Rect bound = bounds.get(i);
                //Is left side is outside the screen
                if (bound.left < leftClip) {
                    int w = bound.right - bound.left;
                    //Try to clip to the screen (left side)
                    clipViewOnTheLeft(bound, w, left);
                    //Except if there's an intersection with the right view
                    Rect rightBound = bounds.get(i + 1);
                    //Intersection
                    if (bound.right + mTitlePadding > rightBound.left) {
                        bound.left = (int) (rightBound.left - w - mTitlePadding);
                        bound.right = bound.left + w;
                    }
                }
            }
        }
        //Right views starting from the current position裁剪右边view
        if (mCurrentPage < countMinusOne) {
            for (int i = mCurrentPage + 1 ; i < count; i++) {
                Rect bound = bounds.get(i);
                //If right side is outside the screen
                if (bound.right > rightClip) {
                    int w = bound.right - bound.left;
                    //Try to clip to the screen (right side)
                    clipViewOnTheRight(bound, w, right);
                    //Except if there's an intersection with the left view
                    Rect leftBound = bounds.get(i - 1);
                    //Intersection
                    if (bound.left - mTitlePadding < leftBound.right) {
                        bound.left = (int) (leftBound.right + mTitlePadding);
                        bound.right = bound.left + w;
                    }
                }
            }
        }
        //Now draw views
        int colorTextAlpha = mColorText >>> 24;
        for (int i = 0; i < count; i++) {
            //Get the title
            Rect bound = bounds.get(i);
            //Only if one side is visible 只画显示出来的
            if ((bound.left > left && bound.left < right) || (bound.right > left && bound.right < right)) {
                final boolean currentPage = (i == page); //page是上面计算的，指明了那个标题该...
                final CharSequence pageTitle = getTitle(i);

                //Only set bold if we are within bounds----setFakeBoldText
                mPaintText.setFakeBoldText(currentPage && currentBold && mBoldText);

                //Draw text as unselected
                mPaintText.setColor(mColorText);
                if(currentPage && currentSelected) {
                    //Fade out/in unselected text as the selected text fades in/out
                    mPaintText.setAlpha(colorTextAlpha - (int)(colorTextAlpha * selectedPercent));
                }

                //Except if there's an intersection with the right view ? 再次检测
                if (i < boundsSize - 1)  {
                    Rect rightBound = bounds.get(i + 1);
                    //Intersection
                    if (bound.right + mTitlePadding > rightBound.left) {
                        int w = bound.right - bound.left;
                        bound.left = (int) (rightBound.left - w - mTitlePadding);
                        bound.right = bound.left + w;
                    }
                }
                canvas.drawText(pageTitle, 0, pageTitle.length(), bound.left, bound.bottom + mTopPadding, mPaintText);

                //If we are within the selected bounds draw the selected text
                if (currentPage && currentSelected) {
                    mPaintText.setColor(mColorSelected);
                    // 渐变的字体颜色
                    mPaintText.setAlpha((int)((mColorSelected >>> 24) * selectedPercent));
                    canvas.drawText(pageTitle, 0, pageTitle.length(), bound.left, bound.bottom + mTopPadding, mPaintText);
                }
            }
        }

        //If we want the line on the top change height to zero and invert the line height to trick the drawing code
        float footerLineHeight = mFooterLineHeight;
        float footerIndicatorLineHeight = mFooterIndicatorHeight;
        if (mLinePosition == LinePosition.Top) {
            height = 0;
            footerLineHeight = -footerLineHeight;
            footerIndicatorLineHeight = -footerIndicatorLineHeight;
        }

        //Draw the footer line
        mPath.reset();
        mPath.moveTo(0, height - footerLineHeight / 2f);
        mPath.lineTo(width, height - footerLineHeight / 2f);
        mPath.close();
        canvas.drawPath(mPath, mPaintFooterLine);

        float heightMinusLine = height - footerLineHeight;
        switch (mFooterIndicatorStyle) {
            case Triangle:
                mPath.reset();
                mPath.moveTo(halfWidth, heightMinusLine - footerIndicatorLineHeight);
                mPath.lineTo(halfWidth + footerIndicatorLineHeight, heightMinusLine);
                mPath.lineTo(halfWidth - footerIndicatorLineHeight, heightMinusLine);
                mPath.close();
                canvas.drawPath(mPath, mPaintFooterIndicator);
                break;
            case Underline:
                if (!currentSelected || page >= boundsSize) {
                    break;
                }
                Rect underlineBounds = bounds.get(page);
                final float rightPlusPadding = underlineBounds.right + mFooterIndicatorUnderlinePadding;
                final float leftMinusPadding = underlineBounds.left - mFooterIndicatorUnderlinePadding;
                final float heightMinusLineMinusIndicator = heightMinusLine - footerIndicatorLineHeight;

                mPath.reset();
                mPath.moveTo(leftMinusPadding, heightMinusLine);
                mPath.lineTo(rightPlusPadding, heightMinusLine);
                mPath.lineTo(rightPlusPadding, heightMinusLineMinusIndicator);
                mPath.lineTo(leftMinusPadding, heightMinusLineMinusIndicator);
                mPath.close();

                mPaintFooterIndicator.setAlpha((int)(0xFF * selectedPercent));
                canvas.drawPath(mPath, mPaintFooterIndicator);
                mPaintFooterIndicator.setAlpha(0xFF);
                break;
        }
    }
    // 基本和之前一样，留着看吧
    public boolean onTouchEvent(android.view.MotionEvent ev) {
        if (super.onTouchEvent(ev)) {
            return true;
        }
        if ((mViewPager == null) || (mViewPager.getAdapter().getCount() == 0)) {
            return false;
        }
        final int action = ev.getAction() & MotionEventCompat.ACTION_MASK;
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
                mLastMotionX = ev.getX();
                break;
            case MotionEvent.ACTION_MOVE: {
                final int activePointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
                final float x = MotionEventCompat.getX(ev, activePointerIndex);
                final float deltaX = x - mLastMotionX;

                if (!mIsDragging) {
                    if (Math.abs(deltaX) > mTouchSlop) {
                        mIsDragging = true;
                    }
                }
                if (mIsDragging) {// 重要！！
                    mLastMotionX = x;
                    if (mViewPager.isFakeDragging() || mViewPager.beginFakeDrag()) {
                        mViewPager.fakeDragBy(deltaX);
                    }
                }
                break;
            }
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                if (!mIsDragging) {
                    final int count = mViewPager.getAdapter().getCount();
                    final int width = getWidth();
                    final float halfWidth = width / 2f;
                    final float sixthWidth = width / 6f;
                    final float leftThird = halfWidth - sixthWidth;
                    final float rightThird = halfWidth + sixthWidth;
                    final float eventX = ev.getX();
                    if (eventX < leftThird) {
                        if (mCurrentPage > 0) {
                            if (action != MotionEvent.ACTION_CANCEL) {
                                mViewPager.setCurrentItem(mCurrentPage - 1);
                            }
                            return true;
                        }
                    } else if (eventX > rightThird) {
                        if (mCurrentPage < count - 1) {
                            if (action != MotionEvent.ACTION_CANCEL) {
                                mViewPager.setCurrentItem(mCurrentPage + 1);
                            }
                            return true;
                        }
                    } else {
                        //Middle third
                        if (mCenterItemClickListener != null && action != MotionEvent.ACTION_CANCEL) {
                            mCenterItemClickListener.onCenterItemClick(mCurrentPage);
                        }
                    }
                }
                mIsDragging = false;
                mActivePointerId = INVALID_POINTER;
                if (mViewPager.isFakeDragging()) mViewPager.endFakeDrag();
                break;
            case MotionEventCompat.ACTION_POINTER_DOWN: {
                final int index = MotionEventCompat.getActionIndex(ev);
                mLastMotionX = MotionEventCompat.getX(ev, index);
                mActivePointerId = MotionEventCompat.getPointerId(ev, index);
                break;
            }
            case MotionEventCompat.ACTION_POINTER_UP:
                final int pointerIndex = MotionEventCompat.getActionIndex(ev);
                final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);
                if (pointerId == mActivePointerId) {
                    final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                    mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
                }
                mLastMotionX = MotionEventCompat.getX(ev, MotionEventCompat.findPointerIndex(ev, mActivePointerId));
                break;
        }
        return true;
    }

    /**
     * Set bounds for the right textView including clip padding.
     *
     * @param curViewBound
     *            current bounds.
     * @param curViewWidth
     *            width of the view.
     */
    private void clipViewOnTheRight(Rect curViewBound, float curViewWidth, int right) {
        curViewBound.right = (int) (right - mClipPadding);
        curViewBound.left = (int) (curViewBound.right - curViewWidth);
    }
    /**
     * Set bounds for the left textView including clip padding.
     *
     * @param curViewBound
     *            current bounds.
     * @param curViewWidth
     *            width of the view.
     */
    private void clipViewOnTheLeft(Rect curViewBound, float curViewWidth, int left) {
        curViewBound.left = (int) (left + mClipPadding);
        curViewBound.right = (int) (mClipPadding + curViewWidth);
    }
    /**
     * Calculate views bounds and scroll them according to the current index
     *
     * @param paint
     * @return
     */
    private ArrayList<Rect> calculateAllBounds(Paint paint) {
        ArrayList<Rect> list = new ArrayList<Rect>();
        //For each views (If no values then add a fake one)
        final int count = mViewPager.getAdapter().getCount();
        final int width = getWidth();
        final int halfWidth = width / 2;
        for (int i = 0; i < count; i++) {
            Rect bounds = calcBounds(i, paint);
            int w = bounds.right - bounds.left;
            int h = bounds.bottom - bounds.top;
            // 1 当静止的时候mPageOffset=0，如果i == mCurrentPage,此时bounds.left的值就是将此子view放于父view中心的位置
            // 2 静止后，如果向左轻轻滑动，那么i == mCurrentPage，- mPageOffset * width的绝对值就是子view左移的长度
            // 3 静止后，如果向右滑动，那么i = mCurrentPage + 1，因此(1- mPageOffset * width)的值就是子view右移的长度，，
            // ，此时，在刚开始滑动时mPageOffset的值是接近1的，因此右移的距离很小，而后，右滑增大，mPageOffset的值也变小,
            //,,因此(1- mPageOffset * width)的值就变大，即向右滑动增大了。
            // 这样实现了跟随viewpager的滑动
            bounds.left = (int)(halfWidth - (w / 2f) + ((i - mCurrentPage - mPageOffset) * width));
            bounds.right = bounds.left + w;
            bounds.top = 0;
            bounds.bottom = h;
            list.add(bounds);
        }
        return list;
    }

    /**
     * Calculate the bounds for a view's title
     *
     * @param index
     * @param paint
     * @return
     */
    private Rect calcBounds(int index, Paint paint) {
        //Calculate the text bounds
        Rect bounds = new Rect();
        CharSequence title = getTitle(index);
        bounds.right = (int) paint.measureText(title, 0, title.length());
        bounds.bottom = (int) (paint.descent() - paint.ascent());
        return bounds;
    }
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        mCurrentPage = position; //随时更新的
        mPageOffset = positionOffset;
        invalidate();
        if (mListener != null) {
            mListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
        }
    }

    @Override
    public void onPageSelected(int position) {
        if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
            mCurrentPage = position;//静止时才会赋值
            invalidate();
        }
        if (mListener != null) {
            mListener.onPageSelected(position);
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        //Measure our width in whatever mode specified
        final int measuredWidth = MeasureSpec.getSize(widthMeasureSpec);
        //Determine our height
        float height;
        final int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightSpecMode == MeasureSpec.EXACTLY) {
            //We were told how big to be
            height = MeasureSpec.getSize(heightMeasureSpec);
        } else {
            //Calculate the text bounds
            mBounds.setEmpty();
            mBounds.bottom = (int) (mPaintText.descent() - mPaintText.ascent());
            height = mBounds.bottom - mBounds.top + mFooterLineHeight + mFooterPadding + mTopPadding;
            if (mFooterIndicatorStyle != IndicatorStyle.None) {
                height += mFooterIndicatorHeight;
            }
        }
        final int measuredHeight = (int)height;
        setMeasuredDimension(measuredWidth, measuredHeight);
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
   // 和前面一样，自定义view时最好写这个方法去维护变量值
}

说明，除了拖动viewpager带动标题栏滚动时，onTouch事件也支持动态改变viewpager的页面，从而

带动标题栏的滑动。可以通过修改，calculateAllBounds中可以修改title间的距离，标题们可以同时多个显示在屏幕上，

并且可以修改比例值改变黑体和透明的变化范围。最终效果可以类似苹果拍照应用的标题效果

2 UnderlinePageIndicator

拖动时显示，出来，之后渐变消失掉

public class UnderlinePageIndicator extends View implements PageIndicator {
    private static final int INVALID_POINTER = -1;
    private static final int FADE_FRAME_MS = 30;
    private final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    private boolean mFades;//是否允许渐消失
    private int mFadeDelay;//当停止后多久开始执行隐藏
    private int mFadeLength;//经过多长时间消失完全
    private int mFadeBy;//每次消失多少

    private ViewPager mViewPager;
    private ViewPager.OnPageChangeListener mListener;
    private int mScrollState;
    private int mCurrentPage;
    private float mPositionOffset;

    private int mTouchSlop;
    private float mLastMotionX = -1;
    private int mActivePointerId = INVALID_POINTER;
    private boolean mIsDragging;

    private final Runnable mFadeRunnable = new Runnable() {
      @Override public void run() {
        if (!mFades) return;
        final int alpha = Math.max(mPaint.getAlpha() - mFadeBy, 0);
        mPaint.setAlpha(alpha);
        invalidate();
        if (alpha > 0) {
          postDelayed(this, FADE_FRAME_MS);
        }
      }
    };

    public UnderlinePageIndicator(Context context) {
        this(context, null);
    }

    public UnderlinePageIndicator(Context context, AttributeSet attrs) {
        this(context, attrs, R.attr.vpiUnderlinePageIndicatorStyle);
    }

    public UnderlinePageIndicator(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        if (isInEditMode()) return;
        final Resources res = getResources();
        // ...
        setFades(a.getBoolean(R.styleable.UnderlinePageIndicator_fades, defaultFades));
        setSelectedColor(a.getColor(R.styleable.UnderlinePageIndicator_selectedColor, defaultSelectedColor));
        setFadeDelay(a.getInteger(R.styleable.UnderlinePageIndicator_fadeDelay, defaultFadeDelay));
        setFadeLength(a.getInteger(R.styleable.UnderlinePageIndicator_fadeLength, defaultFadeLength));
        final ViewConfiguration configuration = ViewConfiguration.get(context);
        mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
    }

    public void setFades(boolean fades) {
        if (fades != mFades) {
            mFades = fades;
            if (fades) {
                post(mFadeRunnable);
            } else {
                removeCallbacks(mFadeRunnable);
                mPaint.setAlpha(0xFF);
                invalidate();
            }
        }
    }
    // mFadeLength / FADE_FRAME_MS 表示执行几次
    public void setFadeLength(int fadeLength) {
        mFadeLength = fadeLength;
        mFadeBy = 0xFF / (mFadeLength / FADE_FRAME_MS);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (mViewPager == null) {
            return;
        }
        final int count = mViewPager.getAdapter().getCount();
        if (count == 0) {
            return;
        }
        if (mCurrentPage >= count) {
            setCurrentItem(count - 1);
            return;
        }
        final int paddingLeft = getPaddingLeft();
        final float pageWidth = (getWidth() - paddingLeft - getPaddingRight()) / (1f * count);
        final float left = paddingLeft + pageWidth * (mCurrentPage + mPositionOffset);
        final float right = left + pageWidth;
        final float top = getPaddingTop();
        final float bottom = getHeight() - getPaddingBottom();
        canvas.drawRect(left, top, right, bottom, mPaint);
    }

    public boolean onTouchEvent(MotionEvent ev) {
        // 高度太小，操作很不便。。。，但还是有了，和之前一样
        return true;
    }

    @Override
    public void setViewPager(ViewPager viewPager) {
        if (mViewPager == viewPager) {
            return;
        }
        if (mViewPager != null) {
            //Clear us from the old pager.
            mViewPager.setOnPageChangeListener(null);
        }
        if (viewPager.getAdapter() == null) {
            throw new IllegalStateException("ViewPager does not have adapter instance.");
        }
        mViewPager = viewPager;
        mViewPager.setOnPageChangeListener(this);
        invalidate();
        post(new Runnable() {
            @Override public void run() {
                if (mFades) {
                    post(mFadeRunnable);
                }
            }
        });
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        mScrollState = state;
        if (mListener != null) {
            mListener.onPageScrollStateChanged(state);
        }
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        mCurrentPage = position;
        mPositionOffset = positionOffset;
        if (mFades) {
            if (positionOffsetPixels > 0) {//表示在滑动，不用执行
                removeCallbacks(mFadeRunnable);
                mPaint.setAlpha(0xFF);
            } else if (mScrollState != ViewPager.SCROLL_STATE_DRAGGING) {//可以执行了
                postDelayed(mFadeRunnable, mFadeDelay);
            }
        }
        invalidate();
        if (mListener != null) {
            mListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
        }
    }

    @Override
    public void onPageSelected(int position) {
        if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {//测试发现一直不满足。。。
            mCurrentPage = position;
            mPositionOffset = 0;
            invalidate();
            mFadeRunnable.run();
        }
        if (mListener != null) {
            mListener.onPageSelected(position);
        }
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
       // 。。。。
}