滑动视图

//滑动视图
public class MyScrollView extends ViewGroup {

    Context context;

    Scroller scroller=null;
    VelocityTracker tracker=null;
    //判断点击还是滑动
    int touchSlop=0;
    //滑动速度临界值
    int minVelocity=0;

    //手指触摸开始位置
    int touchStart=0;
    //手指id
    int mPointerId=0;

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

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

    public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        init(context);
    }

    private void init(Context context) {
        this.context=context;

        scroller=new Scroller(context);

        touchSlop= ViewConfiguration.get(context).getScaledTouchSlop();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        for (int i=0;i<getChildCount();i++) {
            View view=getChildAt(i);
            measureChild(view, widthMeasureSpec, heightMeasureSpec);
        }
        setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        for (int i=0;i<getChildCount();i++) {
            View view=getChildAt(i);
            view.layout(i*getMeasuredWidth(), 0, (i+1)*getMeasuredWidth(), view.getMeasuredHeight());
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touchStart= (int) ev.getX();
                break;
            case MotionEvent.ACTION_MOVE:
                if (Math.abs(ev.getX()-touchStart)>touchSlop) {
                    return true;
                }

        }
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (tracker==null) {
            tracker=VelocityTracker.obtain();
        }
        tracker.addMovement(event);
        //多点触控action
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                //获取索引值为0的手指id
                mPointerId=event.getPointerId(0);
                if (!scroller.isFinished()) {
                    scroller.abortAnimation();
                }
                return true;
            case MotionEvent.ACTION_MOVE:
                //可能在滑动过程中发生了手指变动，即换了一个手指，所以需要每次查找获取新的手指位置
                int index=event.findPointerIndex(mPointerId);
                int temp= (int) event.getX(index);
                scrollBy(-(temp-touchStart), 0);
                touchStart=temp;
                break;
            case MotionEvent.ACTION_UP:
                tracker.computeCurrentVelocity(1000);
                float velocityX=tracker.getXVelocity();
                //向右滑动
                if (velocityX>minVelocity) {

                }
                //向左滑动
                else if (velocityX<-minVelocity) {

                }
                //保留在当前页面
                else {

                }
                if (tracker!=null) {
                    tracker.recycle();
                    tracker=null;
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                //获取离开屏幕的索引值
                int pointerIndexLeave=event.getActionIndex();
                //获取离开屏幕的手指id
                int pointerIdLeave=event.getPointerId(pointerIndexLeave);
                if (pointerIdLeave ==mPointerId) {
                    int reIndex=pointerIndexLeave==0?1:0;
                    mPointerId=event.getPointerId(reIndex);
                    touchStart= (int) event.getX(mPointerId);
                    if (tracker!=null) {
                        tracker.recycle();
                        tracker=null;
                    }
                }
                break;
        }
        return super.onTouchEvent(event);
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        if (scroller.computeScrollOffset()) {
            scrollTo(scroller.getCurrX(), scroller.getCurrY());
            postInvalidate();
        }
    }
}