如何检测scrollview的孩子到达屏幕顶部？

Question

I have ScrollView with many views , how can I know if specific view reached to top of screen after scroll?

I tried this

mScroll.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {

            @Override
            public void onScrollChanged() {

                Rect scrollBounds = new Rect();
                mScroll.getHitRect(scrollBounds);

                if (mView.getLocalVisibleRect(scrollBounds) ) {

                    // if layout even a single pixel, is within the visible area do something
                    //Do someThing
                } else {

                    // if layout goes out or scrolled out of the visible area do something
                    // Do some thing
                }

            }
        });

But this codes detect if the view is out of screen not top of screen

Answer 1

在与所需位置进行比较之后，使用View.getLocationOnScreen()和/或getLocationInWindow() 。

Answer 2

You can create a class to custom ScrollView. In this class, override method onScrollChanged(int l, int t, int oldl, int oldt);

this is my code with vertical ScrollView.

private int rangeEndHeight = 20;
private boolean onEnd = false;

@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
    super.onScrollChanged(l, t, oldl, oldt);
    int length = (int) Math.floor(getContentHeight() * getScale());
    if(getScrollY() >= length - getHeight() - rangeEndHeight) {
        if (!onEnd) {
            onEnd = true;

            // callback here

        }
    }
    else {
        onEnd = false;
    }
}