Flutter StatefulWidget widgets and generics

Question

How can I pass generic type to the State of a StatefulWidget, Here I want to use my generics in myMethod<T>

class MyWidget<T> extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  @override
  Widget build(BuildContext context) {
    return Container();
  }
  
  myMethod<T>(){
    
  }
}

Answer 1

You just provide the type in your state full widget and then pass it way down to its state:

class MyWidget<T> extends StatefulWidget {
  @override
  _MyWidgetState<T> createState() => _MyWidgetState<T>();
}

class _MyWidgetState<T> extends State<MyWidget<T>> {
  @override
  Widget build(BuildContext context) {
    return Container();
  }
  
  myMethod<T>() {
    
  }
}

Usage: MyWidget<String>()

Answer 2

_MyWidgetState need to extends State<MyWidget<T>> not just State<MyWidget> and then you can use T within _MyWidgetState

Answer 3

Here's how the Flutter team solves this issue inside the FutureBuilder widget. Instead of having a return type of _MyWidgetState<T> for the createState(), you would need State<MyWidget<T>>.

State<MyWidget<T>> createState() => _MyWidgetState<T>();