How to pass a function by reference in flutter?-CodePudding

Is there any way to call a function by reference not by values in flutter.

CodePudding user response：

Very nice question indeed, in flutter Function is also first class object so you can pass them around any where.

you do it like

typedef ProfileFormSubmitCallback = void Function(
  String? photoUrl,
  String firstName,
  String lastName,
  String email,
);
then

you can reference your function like,

ProfileFormSubmitCallback myFunction;

CodePudding user response：

Not sure if this is what you mean, but lets say you have a Switch like this

Switch(
  value: false,
  onChanged: (value) {
    print(value);
  },
),

Then onChanged is a function. To use an existing function there instead like

void myFunction(bool value) {
  print(value);
}

you can simply do:

Switch(
  value: false,
  onChanged: myFunction,
),

CodePudding user response：

This is how a function is passed and used. Hope this is what you want

class ButtonPrimary extends StatelessWidget {
  final String text;
  final double? height;
  final double? width;
  final VoidCallback onPressed;
 

  const ButtonPrimary({
    Key? key,
    required this.onPressed,
    required this.text,
    this.height,
    this.width,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: height ?? 50,
      width: width ?? MediaQuery.of(context).size.width * .6,
      child: ElevatedButton(
        onPressed: onPressed,
        child: Widget(...),
      ),
    );
  }
}

And usage,

  ButtonPrimary(
   onPressed: onLoginPressed,
   text: 'Register',
   width: MediaQuery.of(context).size.width * .9,
  )

  ....

  void onLoginPressed() {
    // Do sth
  }