Question 125628 in Android Studio Question posted in
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Android Studio – Getting error as Null check operator used on a null value when variable is made nullable

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);
    
    
        });
      }
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2

Answers


  1. 0

    you have to initialize it in the initState like so:

    class _MyScrollbarState extends State<MyScrollbar> {
     late  ScrollController _scrollController;
   late  ScrollbarPainter _scrollbarPainter;
    
   late Orientation _orientation;
    
      @override
      void initState() {
        super.initState();
        
    _scrollbarPainter = ScrollbarPainter();
    _scrollController = ScrollController();
    _orientation = Orientation();

    //after this you can now use it anywhere inside your widget 
    
        WidgetsBinding.instance.addPostFrameCallback((_) {
    
            _updateScrollPainter(_scrollController!.position);
    
    
        });
      }
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  2. 0

    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();
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