支持侧滑删除的list item实现

一、实现效果图

二、实现的基本思路（不需要重写RecyclerView的touch事件）

1. 自定义ViewGroup，每一个list的item项的根布局都使用自定义的ViewGoup。在其中管理item view和menu view显示的位置。
2. 在自定义的ViewGroup中处理滑动事件，根据滑动事件处理view的移动（item view 和menu view的移动）
3. 使用scroller实现滚动动画，通过设置ViewGroup的scrollX控制显示位置
4. 在自定义ViewGroup中监听recycler view的滚动事件，当发生滚动时关闭item menu

三、具体的实现

计算item view和menu view的大小并设置自定义ViewGroup的大小

 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (getChildCount() != 2) {
            throw new RuntimeException("child count error!You can only add two child view");
        }
        //第一个view是item view，测量大小
        View childView = getChildAt(0);
        measureChild(childView, widthMeasureSpec, heightMeasureSpec);
        //第二个view是menu view，测量大小
        childView = getChildAt(1);
        measureChild(childView, widthMeasureSpec, heightMeasureSpec);
        //设置ViewGroup的大小
        setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec), childView.getMeasuredHeight());
    }

设置item view和menu view的显示位置

protected void onLayout(boolean changed, int l, int t, int r, int b) {
        //自定义ViewGroup只能添加item view和menu view两个子view
        if (getChildCount() != 2) {
            throw new RuntimeException("child count error!You can only add two child view");
        }
        View childView = getChildAt(0);
        //item view填充显示在自定义ViewGroup
        childView.layout(0, 0, childView.getMeasuredWidth(), childView.getMeasuredHeight());
        childView = getChildAt(1);
        //item menu 默认显示在item view的右侧
        childView.layout(getRight(), 0, getRight() + childView.getMeasuredWidth(), childView.getMeasuredHeight());
    }

滑动事件处理通过TouchHelper完成，主要包括onInterceptTouchEvent和onTouchEvent两个方法

    //处理事件的截断处理
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        int action = ev.getActionMasked();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                //取消scroller处理，记录down事件的位置用于计算是否滑动
                scroller.forceFinished(true);
                downX = ev.getX();
                lastX = downX;
                dragFlag = false;
                break;
            case MotionEvent.ACTION_MOVE:
                float currentX = ev.getX();
                lastX = currentX;
                float diffX = Math.abs(currentX - downX);
                //判断是否超过了滑动触发距离
                if (diffX > touchSlop) {
                    dragFlag = true;
                    //通知所有事件都发送到当前view的touch方法
                    view.getParent().requestDisallowInterceptTouchEvent(true);
                }
                break;
        }
        return dragFlag;
    }

    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getActionMasked();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                return false;
            case MotionEvent.ACTION_MOVE: {
                float currentX = event.getX();
                float offsetX = currentX - lastX;
                lastX = currentX;
                View mainView = view.getChildAt(0);
                View menuView = view.getChildAt(1);
                //根据touch事件控制view的滑动，边界条件检查
                offsetX = positionHelper.checkBoundary(view, menuView, offsetX);
                //根据偏移量控制view移动
                positionHelper.moveChild(mainView, menuView, (int) offsetX);
            }
            break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL: {
                float currentX = event.getX();
                direct = (int) (currentX - downX);
                //启动自动滚动到目标位置
                smoothScroll(direct);
            }
            break;
        }
        return true;
    }

通过scroller控制view自动滚动

    public void smoothScroll(int direct) {
        View menuView = view.getChildAt(1);
        //计算到达目标位置的偏移量
        int dx = positionHelper.computeDx(view, menuView, direct);
        if (dx == 0) {
            return;
        }
        //启动scroller计算滚动位置
        scroller.startScroll(positionHelper.getCurrentPosition(menuView), 0, dx, 0);
        //触发下一次的偏移位置计算
        handler.post(runnable);
    }

    public void computeScroll() {
        //判断是否滚动到目标位置
        if (scroller.computeScrollOffset()) {
            int x = scroller.getCurrX();
            View mainView = view.getChildAt(0);
            View menuView = view.getChildAt(1);
            int offset = x - positionHelper.getCurrentPosition(menuView);
            //根据偏移量移动view
            positionHelper.moveChild(mainView, menuView, offset);
            handler.post(runnable);
        }
    }

PositionHelper2实现了移动view的功能

public class PositionHelper2 implements PositionHelper {
    //用于边界检查
    public int checkBoundary(ViewGroup parent, View menuView, float offsetX) {
        int max = menuView.getMeasuredWidth();
        int min = 0;
        int scroll = parent.getScrollX();
        if (scroll - offsetX < min) {
            offsetX = -(min - scroll);
        } else if (scroll - offsetX > max) {
            offsetX = -(max - scroll);
        }
        return (int) offsetX;
    }
    //通过设置mScrollX移动子view的位置
    public void moveChild(View mainView, View menuView, int offsetX){
        ViewGroup parent = (ViewGroup)mainView.getParent();
        parent.scrollBy(-offsetX,0);
    }
    //计算距离目标位置的距离
    public int computeDx(ViewGroup parentView, View menuView, int direct){
        int max = menuView.getMeasuredWidth();
        int scroll = parentView.getScrollX();
        int dx = -direct > 0 ? max - scroll: -scroll;
        return -dx;
    }

    public int getCurrentPosition(View view){
        ViewGroup parent = (ViewGroup)view.getParent();
        return -parent.getScrollX();
    }
}

监听RecyclerView的滚动状态变化，RecyclerView滚动时重置scroll x。

private RecyclerView.OnScrollListener onScrollListener = new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            if (newState == SCROLL_STATE_DRAGGING) {    
                //RecyclerView拖拽时重置scroll x，恢复到原来的位置
                touchHelper.smoothScroll(1);
            }
        }
    };

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        //添加监听
        if (getParent() instanceof RecyclerView) {
            RecyclerView recyclerView = (RecyclerView) getParent();
            recyclerView.addOnScrollListener(onScrollListener);
        }
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        //删除监听
        if (getParent() instanceof RecyclerView) {
            RecyclerView recyclerView = (RecyclerView) getParent();
            recyclerView.removeOnScrollListener(onScrollListener);
        }
    }

四、git 地址

https://github.com/mjlong123123/DragItemViewGroup/tree/dev

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