Flutter/Dart: The argument type 'bool Function(MyStateNotifier)' can't be assigned to the parameter type 'dynamic Function(dynamic)'

Question

I have a such class declaration in Dart, but when using it the compiler reports error

typedef ContextConditionFilter<T, bool> = bool Function(T);

class ContextStateWidget<T extends StateNotifier> extends StatefulWidget
{
    final Widget child;
    final ContextConditionFilter<T, bool> filter;
    const ContextStateWidget({Key key, @required this.child, @required this.filter}) : super(key: key);
}

A class inherited StateNotifier

class MyStateNotifier extends StateNotifier<DrawMenuState>
{
...
bool get myValue => return true;
}

Using it

ContextStateWidget<MyStateNotifier>(
    filter: ((MyStateNotifier notifier) => notifier.myValue), // error here
    child: const OtherWidget()
);

Error

The argument type 'bool Function(MyStateNotifier)' can't be assigned to the parameter type 'dynamic Function(dynamic)'

Solution 1

Thank aligator for your reply, but actually it's analyzer problem. After restart VSCode, the problem gone :-)

Solution 2

There is 2 main problems with your code:

1. You should name the input of the function, for example something like notifier.

typedef ContextConditionFilter<T, V> = V Function(T notifier);

2. You don't need return when using => when defining a function:

class MyStateNotifier extends StateNotifier<DrawMenuState> {
   bool get myValue => true;
}

Everything else should work if you fix these problems.

You also don't need parentheses around your notifier function.

ContextStateWidget<MyStateNotifier>(
    filter: (MyStateNotifier notifier) => notifier.myValue,
    child: const OtherWidget(),
);

Comments

[lenz]

Why not accept the answer? or comment on it?