Getting error as Null check operator used on a null value when variable is made nullable-CodePudding

In the following code for the scrollcontroller, if i initialise the variable _scrollController as late, then I get issue as LateInitializationError: Field '_scrollController@1084415195' has not been initialized. and If i make it nullable, I get Null check operator used on a null value

  class _MyScrollbarState extends State<MyScrollbar> {
       ScrollController? _scrollController;
     ScrollbarPainter? _scrollbarPainter;
    
    Orientation? _orientation;
    
      @override
      void initState() {
        super.initState();
    
        WidgetsBinding.instance.addPostFrameCallback((_) {
    
            _updateScrollPainter(_scrollController!.position);
    
    
        });
      }

CodePudding user response：

you have to initialize it in the init

class _MyScrollbarState extends State<MyScrollbar> {
       ScrollController? _scrollController;
     ScrollbarPainter? _scrollbarPainter;
    
    Orientation? _orientation;
    
      @override
      void initState() {
        super.initState();
        
    _scrollbarPainter = ScrollbarPainter();
    _scrollController = ScrollController();
    //after this you can now use it anywhere inside your widget 
    
        WidgetsBinding.instance.addPostFrameCallback((_) {
    
            _updateScrollPainter(_scrollController!.position);
    
    
        });
      }

State like so:

CodePudding user response：

You need to give them a value so that they dont start as Null. If you give them a default value when you initialize them you should also be able to not use the "?" since now they have a value.

ScrollController _scrollController = ScrollController();
ScrollbarPainter _scrollbarPainter = ScrollbarPainter();