How to declare async function as a variable in flutter(dart)?

Question

In flutter, we can declare a function as variable and call it like this

MyWidget((){print('HI');});

class MyWidget extends StatelessWidget{
  final Function sayHi;

  MyWidget(this.sayHi);

  @override
  Widget build(BuildContext context) {
    sayHi();
    return ...
  }
}

But what if sayHi() is a async function? How to declare a async function as variable? There seems no class like AsyncFunction. So how to achive that?

Answer 1

Async functions are normal functions with some sugar on top. Here, the function variable type just needs to specify that it returns a Future:

class Example {
  Future<void> Function() asyncFuncVar;
  Future<void> asyncFunc() async => print('Do async stuff...');

  Example() {
    asyncFuncVar = asyncFunc;
    asyncFuncVar().then((_) => print('Hello'));
  }
}

void main() => Example();

Hope this helps.