VerticalDragLayout

package com.eoo.eoodemo.taobao;

import android.content.Context;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AbsListView;
import android.widget.FrameLayout;

/**
 * Created by llchen.Andy on 2015/12/18.
 */
public class VerticalDragLayout extends FrameLayout {

    private ViewDragHelper mDragHelper;
    private GestureDetector mGestureDec;

    public VerticalDragLayout(Context context) {
        super(context);
        init();
    }

    public VerticalDragLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public VerticalDragLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        mDragHelper = ViewDragHelper.create(this, new ViewDragHelper.Callback() {

            @Override
            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
                super.onViewPositionChanged(changedView, left, top, dx, dy);
                performViewPositionChanged(changedView, dy);
            }

            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                super.onViewReleased(releasedChild, xvel, yvel);

                performViewReleased(releasedChild, yvel);
            }

            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                return true;
            }

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                int finalTop = top;
                if (child == getChildAt(0)) {
                    finalTop = Math.min(0, top);
                } else {
                    finalTop = Math.max(0, top);
                }

                return (int) (child.getTop() + (finalTop - child.getTop()) * 0.5f);
            }
        });

        mGestureDec = new GestureDetector(getContext(), new GestureDetector.SimpleOnGestureListener() {
            @Override
            public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {

                if (getChildAt(0).getBottom() > 0) {
                    if (canChildScrollDown(getChildAt(0))) {
                        return false;
                    }
                } else if (canChildScrollDown(getChildAt(1)) && distanceY > 0) {
                    return false;
                } else if (canChildScrollUp(getChildAt(1)) && distanceY < 0) {
                    return false;
                }

                return Math.abs(distanceY) > Math.abs(distanceX);
            }
        });
    }

    private void performViewPositionChanged(View changedView, int dy) {

        View targetView = null;
        if (changedView == getChildAt(1)) {
            targetView = getChildAt(0);
        } else {
            targetView = getChildAt(1);
        }

        targetView.offsetTopAndBottom(dy);

        invalidate();
    }

    private void performViewReleased(View changedView, float yvel) {


        if (changedView == getChildAt(0)) {

            log("Top: " + changedView.getTop());

            if (yvel < -1200 || changedView.getTop() < -100) {
                mDragHelper.smoothSlideViewTo(changedView, changedView.getLeft(), -changedView.getMeasuredHeight());
            } else {
                mDragHelper.smoothSlideViewTo(changedView, changedView.getLeft(), 0);
            }
        } else if (changedView == getChildAt(1)) {
            if (yvel > 1200 || changedView.getTop() > 100) {
                mDragHelper.smoothSlideViewTo(changedView, changedView.getLeft(), changedView.getMeasuredHeight());
            } else {
                mDragHelper.smoothSlideViewTo(changedView, changedView.getLeft(), 0);
            }
        }

        ViewCompat.postInvalidateOnAnimation(this);
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        if (mDragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
//        super.onLayout(changed, left, top, right, bottom);

        int topOffset = top;
        for (int i = 0; i < getChildCount(); i++) {
            View childView = getChildAt(i);
            int height = childView.getMeasuredHeight();
            childView.layout(left, topOffset, right, topOffset + height);
            topOffset += childView.getMeasuredHeight();
        }
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {

//        if (getChildAt(0).getBottom() > 0 && getChildAt(0).getTop() < 0) {
//            // view粘到顶部或底部，正在动画中的时候，不处理touch事件
//            return false;
//        }


        boolean shouldIntercept = mDragHelper.shouldInterceptTouchEvent(ev);

        boolean isMoved = mGestureDec.onTouchEvent(ev);


//        log("shouldIntercept: " + shouldIntercept);
//        log("isMoved: " + isMoved);


        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            // action_down时就让mDragHelper开始工作，否则有时候导致异常 他大爷的
            mDragHelper.processTouchEvent(ev);
        }

        return isMoved & shouldIntercept;
    }

    protected boolean canChildScrollDown(View mTargetView) {
        if (android.os.Build.VERSION.SDK_INT < 14) {
            if (mTargetView instanceof AbsListView) {
                final AbsListView absListView = (AbsListView) mTargetView;
                return absListView.getChildCount() > 0
                        && (absListView.getLastVisiblePosition() < absListView.getChildCount() - 1
                        || absListView.getChildAt(absListView.getChildCount() - 1).getBottom() > absListView.getPaddingBottom());
            } else {
                return ViewCompat.canScrollVertically(mTargetView, 1) || mTargetView.getScrollY() < 0;
            }
        } else {
            return ViewCompat.canScrollVertically(mTargetView, 1);
        }
    }

    public boolean canChildScrollUp(View mTargetView) {
        if (android.os.Build.VERSION.SDK_INT < 14) {
            if (mTargetView instanceof AbsListView) {
                final AbsListView absListView = (AbsListView) mTargetView;
                return absListView.getChildCount() > 0
                        && (absListView.getFirstVisiblePosition() > 0 || absListView.getChildAt(0)
                        .getTop() < absListView.getPaddingTop());
            } else {
                return ViewCompat.canScrollVertically(mTargetView, -1) || mTargetView.getScrollY() > 0;
            }
        } else {
            return ViewCompat.canScrollVertically(mTargetView, -1);
        }
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        super.requestDisallowInterceptTouchEvent(disallowIntercept);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mDragHelper.processTouchEvent(event);
        return true;
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();


    }

    private void log(String msg) {
        Log.i("TEST", msg);
    }
}