DART

pass function as parameter in flutter

final VoidCallback onclick;

onPressed: onclick,

take a function as argument flutter

class AClass{
final ReturnType Function(ArgumentType) functionName;
}

flutter send function as parameter

final void Function(int) callback;

dart function as parameter

void doSomething(Function(int) f) {
  f(123);
}

It has the advantage over the function-parameter syntax that you can also use it for variables or anywhere else you want to write a type.

void doSomething(Function(int) f) {
  Function(int) g = f;
  g(123);
}

var x = <int Function(int)>[];

int Function(int) returnsAFunction() => (int x) => x + 1;
    
int Function(int) Function() functionValue = returnsAFunction;