What is the difference between calling the function without parentheses and with parentheses

Question

What is the difference between calling the function without parentheses and with parentheses on onPressed or Ontap?

I just know that void function can\'t be called with

Answer 1

incrementCounter is a reference to the function. You're passing the function along as a parameter to be invoked somewhere later. This is usually used as callback function, if you have a child widget

incrementCounter() will invoke the function call. For this case, your counter will automatically add 1 when the widget builds, which you don't want to happen.

And usually it is not right to call the function directly, you should write it like this:

onPressed: () {
   _incrementCounter();
},

OR

onPressed: () => _incrementCounter();