canScrollVertically 的用法

https://developer.android.com/reference/android/widget/ScrollView
canScrollVertically(-1)返回true的时候表示滑动在滑动到顶部

public boolean canScrollVertically (int direction)

Check if this view can be scrolled vertically in a certain direction.

Parameters
direction   int: Negative to check scrolling up, positive to check scrolling down.
Returns
boolean true if this view can be scrolled in the specified direction, false otherwise.

源码 源码连接

/**
     * Check if this view can be scrolled vertically in a certain direction.
     *
     * @param direction Negative to check scrolling up, positive to check scrolling down.  
     *      小于零是向上滑动，大于零是乡下滑动
     * @return true if this view can be scrolled in the specified direction, false otherwise.
     */
    public boolean canScrollVertically(int direction) {
        final int offset = computeVerticalScrollOffset();
        final int range = computeVerticalScrollRange() - computeVerticalScrollExtent();
        if (range == 0) return false;
        if (direction < 0) {
            return offset > 0;
        } else {
            return offset < range - 1;
        }
    }

判断是否滑动到底部，顶部

/**
     * 判断是否滑动到底部
     * @param direction
     * @return
     */
    private boolean canScrollVerticallyBottomOrTop(int direction) {
       // 判断 scrollView 当前滚动位置在顶部
        if(direction<0){
            if (getScrollY() == 0) {
                return true;
            }  else {
                return false;
            }
        }
            // 判断scrollview 滑动到底部
            // scrollY 的值和子view的高度一样，这人物滑动到了底部
       if(direction>0){
           if (getChildAt(0).getHeight() - getHeight()
                   == getScrollY()) {
               return true;
           } else {
               return false;
           } 
       }
       return false;
    }

处理Scroll View 与竖向滑的ViewPager的滑动冲突

在自定义的Scroll View 中重写 dispatchTouchEvent当Scroll View 滑动到底部的时候把滑动事件交由父控件处理

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_MOVE:
            case MotionEvent.ACTION_DOWN:
                if (canScrollVerticallyBottomOrTop(1)) {
                    getParent().requestDisallowInterceptTouchEvent(false);
                }
                break;
        }
        return super.dispatchTouchEvent(ev);
    }

SwipeRefreshLayout 与 NestedScrollView嵌套使用

  处理多层嵌套  SwipeRefreshLayout >> LinearLayout >>  NestedScrollView 
  的ScrollView滑动不流畅的问题
  解决方案：在SwipeRefreshLayout 重写canChildScrollUp方法 如下：

  /**
     * @return Whether it is possible for the child view of this layout to
     * scroll up. Override this if the child view is a custom view.
     */
    @Override
    public boolean canChildScrollUp() {
        if (scrollView != null)
            return scrollView.canScrollVertically(-1);
        return super.canChildScrollUp();
    }

参考文章

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