NestedScrollView动态设置子View高度不生效

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

        if (!mFillViewport) {
            return;
        }

        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightMode == MeasureSpec.UNSPECIFIED) {
            return;
        }

        if (getChildCount() > 0) {
            View child = getChildAt(0);
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();

            int childSize = child.getMeasuredHeight();
            int parentSpace = getMeasuredHeight()
                    - getPaddingTop()
                    - getPaddingBottom()
                    - lp.topMargin
                    - lp.bottomMargin;

            if (childSize < parentSpace) {
                int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
                        getPaddingLeft() + getPaddingRight() + lp.leftMargin + lp.rightMargin,
                        lp.width);
                int childHeightMeasureSpec =
                        MeasureSpec.makeMeasureSpec(parentSpace, MeasureSpec.EXACTLY);
                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
            }
        }
    }

当child高度小于parent的可用高度时，子view的高度会重置为parentSpace！

如果要修改其子view高度，也要同时修改NestedScrollView的高度。

PS：

    /**
     * When set to true, the scroll view measure its child to make it fill the currently
     * visible area.
     */
    private boolean mFillViewport;

1. 看注释，这个参数的意思就是子view填满父view，但这里都return出去了，子view高度是怎么测量的？

2. 都有 if (childSize < parentSpace){...}，这参数有没有没什么区别吧？