What is the difference between Function and Method in Dart programming language?

Question

I am new to Dart and Flutter, I wanted to know what i the actual difference and when to use which one.

Solution

A function is a top-level function which is declared outside of a class or an inline function that is created inside another function or inside method.

A method is tied to an instance of a class and has an implicit reference to this.

main.dart

// function
void foo() => print('foo'); 

// function
String bar() { 
  return 'bar';
}

void fooBar() {
  int add(int a, int b) => a + b; // inline function

  int value = 0;
  for(var i = 0; i < 9; i++) {
    value = add(value, i); // call of inline function
    print(value);
  }
}

class SomeClass {
  static void foo() => print('foo'); // function in class context sometimes called static method but actually not a method

  SomeClass(this.firstName);

  String firstName;

  // a real method with implicit access to `this`
  void bar() {
    print('${this.firstName} bar');
    print('$firstName bar'); // this can and should be omitted in Dart 
 
    void doSomething() => print('doSomething'); // inline function declared in a method

    doSomething(); // call of inline function  
  }
}

Like inline functions you can also create unnamed inline functions, also called closures. They are often used as callbacks like

button.onClick.listen( /* function start */ (event) {
  print(event.name);
  handleClick();
} /* function end */);