How to give onPressed a method in custom button flutter - dart

Question

i have custom button and i want to add method in my onpressed from my parameter,unfortunately i'm still stuck what type should i use in my custom button parameter, curently i hard code the onpressed method and pass a string route to navigate the problem is not all my button is made to navigate there is one button to logout, i already used void in my parameter but it's still doesn't work.
here is my custom button
FlatButton buttonMenu(String title, IconData icon, String route) {
return new FlatButton(
shape: new RoundedRectangleBorder(
borderRadius: new BorderRadius.circular(25.0)),
color: Colors.blueGrey,
child: new Container(
height: 50.0,
width: 120.0,
child: new Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
new Padding(
padding: EdgeInsets.only(right: 10.0),
child: new Icon(
icon,
color: Colors.white70,
size: 30.0,
),
),
new Text(
title,
style: new TextStyle(fontSize: 20.0, fontWeight: FontWeight.w300),
),
],
),
),
onPressed: () {
Navigator.of(context).pushNamed('/$route');
},
);
}
}
and here is how i call the custom button
buttonMenu('MVP Arc', Icons.star, 'EmployeeScreen')
and what i want is i can send method in my parameter to my onpressed so it will be like this
buttonMenu('MVP Arc', Icons.star, myMethod())
my method for navigate
void _navigate(String route){
Navigator.of(context).pushNamed('/$route');
}

Answer 1

the onPressed type is VoidCallback so make your parameter like this this type.
FlatButton buttonMenu(String title, IconData icon, VoidCallback onCustomButtonPressed )
and when you call it pass a reference to it
buttonMenu('MVP Arc', Icons.star, myMethod)
and don't forget to do the same in your function body
onPressed: onCustomButtonPressed ,
UPDATE:
if you want to pass parameters you have to declare your own Signature :
Example in your case :
typedef VoidNavigate = void Function(String route);
and then use this new type
FlatButton buttonMenu(String title, IconData icon, VoidNavigate onCustomButtonPressed)
call it like this
onPressed: (){onCustomButtonPressed},
and you pass your function like this
buttonMenu('MVP Arc', Icons.star, _navigate('EmployeeScreen'))
or you can just do it like this as #Kirill Shashov said
buttonMenu('MVP Arc', Icons.star, () {_navigate('EmployeeScreen');})

Answer 2

The accepted answer for passing parameters no longer seems to work on newer versions of Flutter.
In case someone searches for a similar issue, the modifications below worked for me.
Modifying Raouf Rahiche's answer, the working method as of 2019. October 28 is as follows.
Update: added mising flutter version number below
Flutter version: 1.9.1+hotfix.5
Dart version: 2.5.0
Using the existing typedef:
typedef VoidNavigate = void Function(String route);
Using the type changed in a small way, you have to pass the parameter to the button separately.
FlatButton buttonMenu(
String title,
IconData icon,
VoidNavigate onCustomButtonPressed,
String route //New addition
) {
...
}
Calling it now:
onPressed: () { onCustomButtonPressed(route); },
Passing the function:
buttonMenu('MVP Arc', Icons.star, _navigate, 'EmployeeScreen')

Answer 3

Here is what worked for me:
Flutter Version : 2.6.0
Dart Version : 2.15.0
in my customButton function:
Widget customButton(VoidCallback onPressed)
{
....
onPressed : onPressed.call(),
}
and no other changes needed.

Answer 4

the only we need to do is add .call() to the end of the function to be void.
onPressed: ()=>onPressed to onPressed: ()=>onPressed.call()