如何在自定义按钮颤动中给 onPressed 一个方法

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()