When using nested Scrollview to collapse a writing project, we encounter a problem. The content in flexible spacebar needs to be displayed dynamically. Some data needs to be returned, which may be hidden. As a result, the height is uncertain. However, expandedheight in slicerappbar can only be fixed, so we have to find another way to obtain the height.

copy a copy of the code in flexible space bar and write it into a statelesswidget to set a globalkey. Now you need to process the request, write it in the successful callback, and use the first frame of the successful request to get the height

WidgetsBinding.instance.addPostFrameCallback((_) {
      RenderBox _cardBox =
          _flexibleSpaceBarKey.currentContext.findRenderObject();

      Future.delayed(Duration(milliseconds: 10), () {
        setState(() {
          heightFlexibleSpaceBar = _cardBox.size.height;
        });
      });
    });