最近有个需求webview滚动到顶部及底部触发一些操作，从网上找的例子都不太满意，主要有几点问题需要完善：

1.webview滚动到顶部或底部，应该是抬手后触发。

2.当H5内容高度小于webview本身设置的高度，页面不滚动，该如何触发顶部及底部动作。

最终效果

public class NestedWebView extends WebView {
    //默认开始是顶部
    boolean isScrolledToTop = true;
    boolean isScrolledToBottom = false;
    ScrollInterface mScrollInterface;

    private int y = 0;
    public NestedWebView(Context context) {
        super(context);
    }

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

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if(event.getAction() == MotionEvent.ACTION_DOWN){
            y = (int) event.getY();
        }
        if (event.getAction() == MotionEvent.ACTION_UP) {
            if(mScrollInterface != null){
                Log.e("webScroll","y:"+event.getY());
                int upTmp = y - (int)event.getY() ;
                int downTmp = (int)event.getY() - y;
                if (isScrolledToTop && downTmp > 10) {
                    // 触发滚动到顶部的事件
                    // 在这里添加你需要执行的逻辑
                    mScrollInterface.scrollTop();
                } else if (isScrolledToBottom && upTmp > 10) {
                    // 触发滚动到底部的事件
                    // 在这里添加你需要执行的逻辑
                    mScrollInterface.scrollBottom();
                }
            }

        }
        return super.onTouchEvent(event);
    }

    public void initStatus(){
        isScrolledToTop = true;
        int contentHeight = (int) (this.getContentHeight() * this.getScale());
        int webViewHeight = this.getHeight();
        if(contentHeight <= webViewHeight){
            isScrolledToBottom = true;
            FrameLayout.LayoutParams ps = new FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT,FrameLayout.LayoutParams.MATCH_PARENT);
            ps.rightMargin = SizeUtils.dpToPx(48);
            this.setLayoutParams(ps);

        }
    }


    @Override
    protected void onScrollChanged(int l, int scrollY, int oldl, int oldt) {
        super.onScrollChanged(l, scrollY, oldl, oldt);
        int contentHeight = (int) (this.getContentHeight() * this.getScale());
        int webViewHeight = this.getHeight();
        if (scrollY == 0) {
            isScrolledToTop = true;
            isScrolledToBottom = false;
        } else if (scrollY >= contentHeight - webViewHeight) {
            isScrolledToTop = false;
            isScrolledToBottom = true;
        } else {
            isScrolledToTop = false;
            isScrolledToBottom = false;
        }
    }
    public void setOnCustomScrollChangeListener(ScrollInterface mInterface) {
        mScrollInterface = mInterface;
    }
    public interface ScrollInterface {
        void scrollTop();
        void scrollBottom();
    }
}