// @dart=2.12 void doSomething<T>() { List<List<T>> pages = []; print(pages.runtimeType.toString()); } void main() { doSomething<String>(); } Result JSArray<List<String>> solved Null Safety equivalent of “List()”? [duplicate]
This is declaring a local variable: AnimationController _animationController = AnimationController(vsync: this, duration: Duration(milliseconds: 500)); What you want is assign to your existing class member variable: _animationController = AnimationController(vsync: this, duration: Duration(milliseconds: 500)); solved Dart throws LateInitializationError even when I initialize variables in initState