// function with parameter example in dart void addTwoNumber(int x, int y) { print('Sum is: ${x+y}'); } void main() { addTwoNumber(10,3); addTwoNumber(20,10); addTwoNumber(20,5); } final VoidCallback onclick; onPressed: onclick,class AClass{ final ReturnType Function(ArgumentType) functionName; }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;