What does the empty parentheses after the onPressed property mean in Dart?

Question

I know the syntax for calling a function after onPressed and onTap for a widget. There are two options We can use either the () => functio

Answer 1

If I understand your question correctly, you are asking about the bolded one () => function().

With that assumption I am trying to answer.

onTap, onPressed are the taking function as arguments. Possible values can be

func callbackFunction() {
 // what ever we want to do onTap
}

1. onTap: callbackFunction

2. onTap: () => callbackFunction() // onTap: callbackFunction() it will invoke the method while building itself. 
                                   // So we are making it lazy by wrapping in another anonymous function. 

3. onTap: () { callbackFunction(); }

4. onTap: () => print("tapped")   // anonymous one line function

5. onTap: () { print("tapped"); 
               // what ever we want to do onTap
               print("tapped"); 
           }   // anonymous multiline function