dependOnInheritedWidgetOfExactType() returns null

Question

I tried to send the property of my InheritedWidget to its child.

class Detector extends InheritedWidget {
  final bool isEditable;

  Detector({@required this.isEditable, @required Widget child, Key key})
      : super(child: child, key: key);

  static Detector of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<Detector>();
  }

  @override
  bool updateShouldNotify(Detector oldWidget) {
    return oldWidget.isEditable != isEditable;
  }
}

I referred here. The widget is created by:

Detector(
  isEditable: otherObj.isEditable,
  child: command.makeWidget(context) // Extension method that returns new widget
);

And makeWidget() method calls the of method:

   final detector = Detector.of(context);
    if (detector != null && detector.isEditable) {
      return Container(
        child: ...,
      );
    }

always returns null. Why does dependOnInheritedWidgetOfExactType() return null? I use the extension method but give it the context from an ancestor widget.

Answer 1

That's one of the reasons you shouldn't use functions instead of classes to make reusable widgets. What is the difference between functions and classes to create widgets?

You are calling dependOnInheritedWidgetOfExactType<Detector> on a BuildContext that is an ancestor of Detector.

Instead of:

Detector(
  isEditable: otherObj.isEditable,
  child: command.makeWidget(context) // Extension method that returns new widget
);

refactor command.makeWidget(context) such that it's a StatelessWidget class instead of a function.

That will give you a BuildContext that is a descendant of Detector and will fix your issue.