PagerTab.java

package com.nonobank.ui.widget;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.support.v4.view.ViewCompat;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.support.v4.widget.EdgeEffectCompat;
import android.support.v4.widget.ScrollerCompat;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.ViewTreeObserver;
import android.widget.ImageButton;
import android.widget.TextView;

import com.nonobank.R;
import com.nonobank.common.utils.LogUtils;
import com.nonobank.ui.activity.BaseActivity;
import com.nonobank.utils.UIUtils;

/**
 * <p>Created by mio on 14-12-26. </p>
 * **如果要实现ViewPager的OnPageChangeListener请使用PagerTab的OnPageChangeListener**
 */
public class PagerTab extends ViewGroup {

    private ViewPager mViewPager;
    private PageListener mPageListener = new PageListener ();//用于注册给ViewPager监听状态和滚动
    /**
     * 外界设置的OnPageChangeListener(委托)--PageTab设置的
     */
    private OnPageChangeListener mDelegatePageListener;

    /**
     * 分割线上下的padding
     */
    private int mDividerPadding = 12;
    private int mDividerWidth = 1;
    private int mDividerColor = 0x1A000000;//分割线颜色
    private Paint mDividerPaint;//分割线的画笔

    /**
     * 指示器的高度
     */
    private int mIndicatorHeight = 4;
    private int mIndicatorWidth;//指示器的宽度，是动态的随着tab的宽度变化
    private int mIndicatorLeft;//指示器的距离左边的距离
    private int mIndicatorColor = 0xff96b63c;//指示器颜色
    private Paint mIndicatorPaint; //指示器的画笔

    private int mContentWidth;//记录自身内容的宽度
    private int mContentHeight;//记录自身内容的高度

    /**
     * tab左右的内边距
     */
    private int mTabPadding = 24;
    private int mTabTextSize = 16; //tab文字大小
    private int mTabBackgroundResId = R.drawable.bg_tab_text;// tab背景资源
    private int mTabTextColorResId = R.color.tab_text_color; //tab文字颜色
    private int mTabCount;//tab的个数

    private int mCurrentPosition = 0;//当前光标所处的tab，规则是以光标的最左端所在的item的position
    private float mCurrentOffsetPixels;//光标左边距离当前光标所处的tab的左边距离
    private int mSelectedPosition = 0; //当前被选中的tab，用于记录手指点击tab的position

    private boolean mIsBeingDragged = false;//是否处于拖动中
    private float mLastMotionX;//上一次手指触摸的x坐标
    private VelocityTracker mVelocityTracker;//用于记录速度的帮助类
    private int mMinimumVelocity;//系统默认的最小满足fling的速度
    private int mMaximumVelocity;//系统默认最大的fling速度
    private int mTouchSlop;//系统默认满足滑动的最小位移

    /**
     * 处理滚动的帮助者
     */
    private ScrollerCompat mScroller;
    private int mLastScrollX;//记录上一次滚动的x位置，这是用于处理overScroll，实际位置可能会受到限制

    private int mMaxScrollX = 0;// 控件最大可滚动的距离
    private int mSplitScrollX = 0;// 根据item的个数，计算出每移动一个item控件需要移动的距离

    /**
     * 处理overScroll的反馈效果,类似ViewPager滑到头有效果
     */
    private EdgeEffectCompat mLeftEdge;
    private EdgeEffectCompat mRightEdge;
    private int defalutPosition = 0;

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

    public PagerTab(Context context, AttributeSet attrs) {
        this (context, attrs, 0);
    }

    public PagerTab(Context context, AttributeSet attrs, int defStyle) {
        super (context, attrs, defStyle);
        init ();
        initPaint ();
    }

    /**
     * 初始化一些常量
     */
    private void init() {
        //把一个值从dip转换成px
        mIndicatorHeight = UIUtils.dip2px (mIndicatorHeight);
        mDividerPadding = UIUtils.dip2px (mDividerPadding);
        mTabPadding = UIUtils.dip2px (mTabPadding);
        mDividerWidth = UIUtils.dip2px (mDividerWidth);
        mTabTextSize = UIUtils.dip2px (mTabTextSize);
        //创建一个scroller
        mScroller = ScrollerCompat.create (getContext ());
        //获取一个系统关于View的常量配置类
        final ViewConfiguration configuration = ViewConfiguration.get (getContext ());
        //获取滑动的最小距离
        mTouchSlop = configuration.getScaledTouchSlop ();
        //获取fling的最小速度
        mMinimumVelocity = configuration.getScaledMinimumFlingVelocity ();
        //获取fling的最大速度
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity ();

        mLeftEdge = new EdgeEffectCompat (getContext ());
        mRightEdge = new EdgeEffectCompat (getContext ());
    }

    /**
     * 初始画笔
     */
    private void initPaint() {
        mIndicatorPaint = new Paint ();
        mIndicatorPaint.setAntiAlias (true);
        mIndicatorPaint.setStyle (Paint.Style.FILL);
        mIndicatorPaint.setColor (mIndicatorColor);

        mDividerPaint = new Paint ();
        mDividerPaint.setAntiAlias (true);
        mDividerPaint.setStrokeWidth (mDividerWidth);
        mDividerPaint.setColor (mDividerColor);
    }

    /**
     * 设置ViewPager
     */
    public void setViewPager(ViewPager viewPager) {
        if (viewPager == null || viewPager.getAdapter () == null) {
            throw new IllegalStateException ("ViewPager is null or ViewPager does not have adapter instance.");
        }
        mViewPager = viewPager;
        onViewPagerChanged ();
    }

    private void onViewPagerChanged() {
        mViewPager.setOnPageChangeListener (mPageListener);//给ViewPager设置监听
        mTabCount = mViewPager.getAdapter ().getCount ();//有多少个tab需要看ViewPager有多少个页面

        for(int i = 0; i < mTabCount; i++) {
            if (mViewPager.getAdapter () instanceof IconTabProvider) {//如果想要使用icon作为tab，则需要adapter实现IconTabProvider接口
                addIconTab (i, ((IconTabProvider) mViewPager.getAdapter ()).getPageIconResId (i));
            } else {
                addTextTab (i, mViewPager.getAdapter ().getPageTitle (i).toString ());
            }
        }
        ViewTreeObserver viewTreeObserver = getViewTreeObserver ();
        if (viewTreeObserver != null) {//监听第一个的全局layout事件，来设置当前的mCurrentPosition，显示对应的tab
            viewTreeObserver.addOnGlobalLayoutListener (new ViewTreeObserver.OnGlobalLayoutListener () {
                @Override
                public void onGlobalLayout() {
                    getViewTreeObserver ().removeGlobalOnLayoutListener (this);//只需要监听一次，之后通过listener回调即可
                    mCurrentPosition = mViewPager.getCurrentItem ();
                    if (mDelegatePageListener != null) {
                        mDelegatePageListener.onPageSelected (mCurrentPosition);
                    }
                }
            });
        }
    }

    /**
     * 设置监听，因为Tab会监听ViewPager的状态，所以不要给ViewPager设置监听了，设置给Tab，由Tab转发
     */
    public void setOnPageChangeListener(OnPageChangeListener listener) {
        mDelegatePageListener = listener;
    }

    /**
     * 添加文字tab
     */
    private void addTextTab(final int position, String title) {

        TextView tab = new TextView (getContext ());
        tab.setText (title);
        tab.setGravity (Gravity.CENTER);
        tab.setSingleLine ();
        tab.setTextSize (TypedValue.COMPLEX_UNIT_PX, mTabTextSize);
        tab.setTypeface (Typeface.defaultFromStyle (Typeface.BOLD));
        tab.setTextColor (UIUtils.getColorStateList (mTabTextColorResId));
        tab.setBackgroundDrawable (UIUtils.getDrawable (mTabBackgroundResId));
        tab.setLayoutParams (new LayoutParams (LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT));
        //默认第1个tab是选中状态
        if (position == defalutPosition) {
            tab.setSelected (true);
            mViewPager.setCurrentItem (defalutPosition);
        }
        addTab (position, tab);
    }

    /**
     * 添加图片icon
     */
    private void addIconTab(final int position, int resId) {
        ImageButton tab = new ImageButton (getContext ());
        tab.setImageResource (resId);
        tab.setLayoutParams (new LayoutParams (LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
        addTab (position, tab);
    }

    /**
     * 将Tab添加到自身 & 添加点击事件  *
     */
    private void addTab(final int position, View tab) {
        tab.setFocusable (true);
        //设置tab的点击事件，当tab被点击时候切换pager的页面
        tab.setOnClickListener (new OnClickListener () {
            @Override
            public void onClick(View v) {
                mViewPager.setCurrentItem (position);
            }
        });
        tab.setPadding (mTabPadding, 0, mTabPadding, 0);
        addView (tab, position);
    }

    /**
     * 测量时的回调
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // 获取控件自身的宽高,模式
        int widthSize = MeasureSpec.getSize (widthMeasureSpec) - getPaddingLeft () - getPaddingRight ();
        int heightSize = MeasureSpec.getSize (heightMeasureSpec) - getPaddingBottom () - getPaddingBottom ();
        int widthMode = MeasureSpec.getMode (widthMeasureSpec);
        int heightMode = MeasureSpec.getMode (heightMeasureSpec);

        int totalWidth = 0;
        int highest = 0;
        int goneChildCount = 0;
        for(int i = 0; i < mTabCount; i++) {
            final View child = getChildAt (i);
            if (child == null || child.getVisibility () == View.GONE) {
                goneChildCount++;
                continue;
            }
            int childWidthMeasureSpec;
            int childHeightMeasureSpec;

            LayoutParams childLayoutParams = child.getLayoutParams ();
            if (childLayoutParams == null) {
                childLayoutParams = new LayoutParams (LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
            }

            if (childLayoutParams.width == LayoutParams.MATCH_PARENT) {
                childWidthMeasureSpec = MeasureSpec.makeMeasureSpec (widthSize, MeasureSpec.EXACTLY);
            } else if (childLayoutParams.width == LayoutParams.WRAP_CONTENT) {
                childWidthMeasureSpec = MeasureSpec.makeMeasureSpec (widthSize, MeasureSpec.AT_MOST);
            } else {
                childWidthMeasureSpec = MeasureSpec.makeMeasureSpec (childLayoutParams.width, MeasureSpec.EXACTLY);
            }

            if (childLayoutParams.height == LayoutParams.MATCH_PARENT) {
                childHeightMeasureSpec = MeasureSpec.makeMeasureSpec (heightSize, MeasureSpec.EXACTLY);
            } else if (childLayoutParams.height == LayoutParams.WRAP_CONTENT) {
                childHeightMeasureSpec = MeasureSpec.makeMeasureSpec (heightSize, MeasureSpec.AT_MOST);
            } else {
                childHeightMeasureSpec = MeasureSpec.makeMeasureSpec (childLayoutParams.height, MeasureSpec.EXACTLY);
            }

            child.measure (childWidthMeasureSpec, childHeightMeasureSpec);

            int childWidth = child.getMeasuredWidth ();
            int childHeight = child.getMeasuredHeight ();

            totalWidth += childWidth;
            highest = highest < childHeight ? childHeight : highest;
        }

        if (totalWidth <= widthSize) {//如果子Tab的总宽度小于PagerTab，则采用平分模式
            int splitWidth = (int) (widthSize / (mTabCount - goneChildCount + 0.0f) + 0.5f);
            for(int i = 0; i < mTabCount; i++) {
                final View child = getChildAt (i);
                if (child == null || child.getVisibility () == View.GONE) {
                    continue;
                }
                int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec (splitWidth, MeasureSpec.EXACTLY);
                int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec (child.getMeasuredHeight (), MeasureSpec.EXACTLY);
                child.measure (childWidthMeasureSpec, childHeightMeasureSpec);
            }
            mMaxScrollX = 0;
            mSplitScrollX = 0;
        } else {//如果所有子View大于控件的宽度
            mMaxScrollX = totalWidth - widthSize;
            mSplitScrollX = (int) (mMaxScrollX / (mTabCount - goneChildCount - 1.0f) + 0.5f);
        }

        if (widthMode == MeasureSpec.EXACTLY) {
            mContentWidth = widthSize;
        } else {
            mContentWidth = totalWidth;
        }

        if (heightMode == MeasureSpec.EXACTLY) {
            mContentHeight = heightSize;
        } else {
            mContentHeight = highest;
        }

        int measureWidth = mContentWidth + getPaddingLeft () + getPaddingRight ();
        int measureHeight = mContentHeight + getPaddingTop () + getPaddingBottom ();
        setMeasuredDimension (measureWidth, measureHeight);
    }

    /**
     * 布局时的回调
     */
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {//这里简化了，没有考虑margin的情况
        if (changed) {
            int height = b - t;//控件供子View显示的高度
            int left = l;
            for(int i = 0; i < mTabCount; i++) {
                final View child = getChildAt (i);
                if (child == null || child.getVisibility () == View.GONE) {
                    continue;
                }
                int top = (int) ((height - child.getMeasuredHeight ()) / 2.0f + 0.5f);//如果控件比tab要高，则居中显示
                int right = left + child.getMeasuredWidth ();
                child.layout (left, top, right, top + child.getMeasuredHeight ());//摆放tab
                left = right;//因为是水平摆放的，所以为下一个准备left值
            }
        }
    }

    /**
     * 绘制时的回调
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw (canvas);
        final int height = getHeight ();
        //画指示器
        canvas.drawRect (mIndicatorLeft, height - mIndicatorHeight, mIndicatorLeft + mIndicatorWidth, height, mIndicatorPaint);

        // 画分割线
        for(int i = 0; i < mTabCount - 1; i++) {//分割线的个数比tab的个数少一个
            final View child = getChildAt (i);
            if (child == null || child.getVisibility () == View.GONE) {
                continue;
            }
            if (child != null) {
                canvas.drawLine (child.getRight (), mDividerPadding, child.getRight (), mContentHeight - mDividerPadding, mDividerPaint);
            }
        }
        // 因为overScroll效果是一个持续效果，所以需要持续画--参见ViewPager源码
        boolean needsInvalidate = false;
        if (!mLeftEdge.isFinished ()) {//如果效果没停止
            final int restoreCount = canvas.save ();//先保存当前画布
            final int heightEdge = getHeight () - getPaddingTop () - getPaddingBottom ();
            final int widthEdge = getWidth ();
            canvas.rotate (270);
            canvas.translate (-heightEdge + getPaddingTop (), 0);
            mLeftEdge.setSize (heightEdge, widthEdge);
            needsInvalidate |= mLeftEdge.draw (canvas);
            canvas.restoreToCount (restoreCount);
        }
        if (!mRightEdge.isFinished ()) {
            final int restoreCount = canvas.save ();
            final int widthEdge = getWidth ();
            final int heightEdge = getHeight () - getPaddingTop () - getPaddingBottom ();
            canvas.rotate (90);
            canvas.translate (-getPaddingTop (), -(widthEdge + mMaxScrollX));
            mRightEdge.setSize (heightEdge, widthEdge);
            needsInvalidate |= mRightEdge.draw (canvas);
            canvas.restoreToCount (restoreCount);
        }
        if (needsInvalidate) {
            postInvalidate ();
        }
    }

    /**
     * 触摸事件是否拦截的方法
     */
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        final int action = ev.getAction ();
        if (mIsBeingDragged && action == MotionEvent.ACTION_MOVE) {//当已经处于拖动，并且当前事件是MOVE，直接消费掉
            return true;
        }
        switch (action) {
            case MotionEvent.ACTION_DOWN: {
                final float x = ev.getX ();
                mLastMotionX = x; //记录住当前的x坐标
                mIsBeingDragged = !mScroller.isFinished ();//如果按下的时候还在滚动，则把状态处于拖动状态
                LogUtils.d ("onInterceptTouchEvent--->mIsBeingDragged:"+mIsBeingDragged);
                break;
            }
            case MotionEvent.ACTION_MOVE: {
                final float x = ev.getX ();
                final int xDiff = (int) Math.abs (x - mLastMotionX);//计算两次的差值
                if (xDiff > mTouchSlop) {//如果大于最小移动的距离，则把状态改变为拖动状态
                    mIsBeingDragged = true;
                    mLastMotionX = x;
                    ViewParent parent = getParent ();//并请求父View不要再拦截自己触摸事件，交给自己处理
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent (true);
                    }
                }
                break;
            }
            case MotionEvent.ACTION_CANCEL://当手指离开或者触摸事件取消的时候，把拖动状态取消掉
            case MotionEvent.ACTION_UP:
                mIsBeingDragged = false;
                break;
        }
        LogUtils.d ("onInterceptTouchEvent--->mIsBeingDragged before return :"+mIsBeingDragged);
        return mIsBeingDragged;//如果是拖动状态，则拦截事件，交给自己的onTouch处理
    }

    /**
     * 触摸事件的处理方法
     */
    public boolean onTouchEvent(MotionEvent ev) {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain ();
        }
        mVelocityTracker.addMovement (ev);
        final int action = ev.getAction ();
        switch (action) {
            case MotionEvent.ACTION_DOWN: {//如果是down事件，记录住当前的x坐标

                final float x = ev.getX ();
                if (!mScroller.isFinished ()) {
                    mScroller.abortAnimation ();
                }
                mLastMotionX = x;
                break;
            }
            case MotionEvent.ACTION_MOVE: {
                final float x = ev.getX ();
                final float deltaX = x - mLastMotionX;
//                if (!mIsBeingDragged) {//如果还没有处于拖动，则判断两次的差值是否大于最小拖动的距离
//                    if (Math.abs (deltaX) > mTouchSlop) {
//                        mIsBeingDragged = true;
//                    }
//                }
                if (mIsBeingDragged) {//如果处于拖动状态，记录住x坐标
                    mLastMotionX = x;
                    onMove (deltaX);
                }
                break;
            }
            case MotionEvent.ACTION_UP: {
                if (mIsBeingDragged) {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    //先对速度进行一个调整，第一个参数是时间单位，1000毫秒，第二个参数是最大速度。
                    velocityTracker.computeCurrentVelocity (1000, mMaximumVelocity);
                    float velocity = velocityTracker.getXVelocity ();//获取水平方向上的速度
                    onUp (velocity);
                }
            }
            case MotionEvent.ACTION_CANCEL: {
                mIsBeingDragged = false;
                if (mVelocityTracker != null) {
                    mVelocityTracker.recycle ();
                    mVelocityTracker = null;
                }
                break;
            }
        }
        return true;
    }

    private void onMove(float x) {
        if (mMaxScrollX <= 0) {
            if (mViewPager.isFakeDragging () || mViewPager.beginFakeDrag ()) { //模拟ViewPager的拖拽效果
                mViewPager.fakeDragBy (x);
            }
        } else {
            int scrollByX = -(int) (x + 0.5);
            if (getScrollX () + scrollByX < 0) {
                scrollByX = 0 - getScrollX ();
                mLeftEdge.onPull (Math.abs (x) / getWidth ());
            }
            if (getScrollX () + scrollByX > mMaxScrollX) {
                scrollByX = mMaxScrollX - getScrollX ();
                mRightEdge.onPull (Math.abs (x) / getWidth ());
            }
            scrollBy (scrollByX, 0);
            ViewCompat.postInvalidateOnAnimation (this);
        }
    }

    private void onUp(float velocity) {
        if (mMaxScrollX <= 0) {
            if (mViewPager.isFakeDragging ()) mViewPager.endFakeDrag ();
        } else {
            if (Math.abs (velocity) <= mMinimumVelocity) {
                return;
            }
            mScroller.fling (getScrollX (), 0, -(int) (velocity + 0.5), 0, 0, mMaxScrollX, 0, 0, 270, 0);
            ViewCompat.postInvalidateOnAnimation (this);
        }
    }

    @Override
    public void computeScroll() {
        if (!mScroller.isFinished() && mScroller.computeScrollOffset ()) {
            int oldX = mLastScrollX;
            mLastScrollX = mScroller.getCurrX ();
            if (mLastScrollX < 0 && oldX >= 0) {
                mLeftEdge.onAbsorb ((int) mScroller.getCurrVelocity ());
            } else if (mLastScrollX > mMaxScrollX && oldX <= mMaxScrollX) {
                mRightEdge.onAbsorb ((int) mScroller.getCurrVelocity ());
            }
            int x = mLastScrollX;
            if (mLastScrollX < 0) {
                x = 0;
            } else if (mLastScrollX > mMaxScrollX) {
                x = mMaxScrollX;
            }
            scrollTo (x, 0);
            ViewCompat.postInvalidateOnAnimation (this);
        }
    }

    /**
     * 检测mIndicatorOffset的合法性，并计算出其他有关tab的属性值
     */
    private void checkAndcalculate() {
        // 如果指示器起始位置比第一个tab的起始位置还要小，纠正为第一个tab的起始位置，指示器宽度就是第一个tab的宽度
        final View firstTab = getChildAt (0);
        if (mIndicatorLeft < firstTab.getLeft ()) {
            mIndicatorLeft = firstTab.getLeft ();
            mIndicatorWidth = firstTab.getWidth ();
        }
        // 如果指示器起始位置比最后一个tab的起始位置还要大，纠正为最后一个tab的起始位置，指示器宽度就是最后一个tab的宽度
        View lastTab = getChildAt (mTabCount - 1);
        if (mIndicatorLeft > lastTab.getLeft ()) {
            mIndicatorLeft = lastTab.getLeft ();
            mIndicatorWidth = lastTab.getWidth ();
        }
        // 通过指示器的起始位置计算出当前处于第几个position，并且计算出已经偏移了多少，偏移量是以当前所处的tab的宽度的百分比
        for(int i = 0; i < mTabCount; i++) {
            View tab = getChildAt (i);
            if (mIndicatorLeft < tab.getLeft ()) {
                mCurrentPosition = i - 1;
                View currentTab = getChildAt (mCurrentPosition);
                mCurrentOffsetPixels = (mIndicatorLeft - currentTab.getLeft ()) / (currentTab.getWidth () + 0.0f);
                break;
            }
        }
    }

    /**
     * 滚动到指定的child
     */
    public void scrollSelf(int position, float offset) {
        if (position >= mTabCount) {
            return;
        }
        final View tab = getChildAt (position);
        mIndicatorLeft = (int) (tab.getLeft () + tab.getWidth () * offset + 0.5);
        int rightPosition = position + 1;
        if (offset > 0 && rightPosition < mTabCount) {
            View rightTab = getChildAt (rightPosition);
            mIndicatorWidth = (int) (tab.getWidth () * (1 - offset) + rightTab.getWidth () * offset + 0.5); //Indicator的宽度根据Viewpager的offset决定
        } else {
            mIndicatorWidth = tab.getWidth ();
        }
        checkAndcalculate ();

        int newScrollX = position * mSplitScrollX + (int) (offset * mSplitScrollX + 0.5);
        if (newScrollX < 0) {
            newScrollX = 0;
        }
        if (newScrollX > mMaxScrollX) {
            newScrollX = mMaxScrollX;
        }
        int duration = 100;
        if (mSelectedPosition != -1) {
            duration = (Math.abs (mSelectedPosition - position)) * 100;
        }
        mScroller.startScroll (getScrollX (), 0, (newScrollX - getScrollX ()), 0, duration);
        ViewCompat.postInvalidateOnAnimation (this);
    }

    /**
     * 选中指定位置的Tab
     */
    private void selectTab(int position) {
        for(int i = 0; i < mTabCount; i++) {
            View tab = getChildAt (i);
            if (tab != null) {
                tab.setSelected (position == i);
            }
        }
    }

    /**
     * ViewPager的OnPageChangeListener实现类，因为我们需要在PagerTab中获取PagerView的监听，以便可以调整tab
     */
    private class PageListener implements OnPageChangeListener {
        @Override
        public void onPageScrolled(int position, float positionOffset, final int positionOffsetPixels) {
            //根据VierPager的偏移值来滚动tab
            scrollSelf (position, positionOffset);
            if (mDelegatePageListener != null) {//这个是提供给外部的
                mDelegatePageListener.onPageScrolled (position, positionOffset, positionOffsetPixels);
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            if (state == ViewPager.SCROLL_STATE_IDLE) {
                mSelectedPosition = -1;
            }
            if (mDelegatePageListener != null) {
                mDelegatePageListener.onPageScrollStateChanged (state);
            }
        }

        @Override
        public void onPageSelected(int position) {
            LogUtils.d ("PagerTab-> onPageSelected:" + position);
            mSelectedPosition = position;
            selectTab (position);
            if (mDelegatePageListener != null) {
                mDelegatePageListener.onPageSelected (position);
            }
        }
    }

    /**
     * 如果指示器希望是图片，则继承该接口
     */
    public interface IconTabProvider {
        public int getPageIconResId(int position);

        public int getPageSelectedIconResId();
    }
}