Difference between a method called with a parameter and a method called with none

Question

please what's the difference between a method called with a parameter and one called with no parameter example:

state is! LoginInProgress ? _onLoginButtonPressed : null,

and:

state is! LoginInProgress ? _onLoginButtonPressed(): null,

these two statements have different functionalities in my code execution, _onLoginButtonPressed and _onLoginButtonPressed() i mean, please I would really apricate if I can get the difference between the two, thanks in advance.

Answer 1

When a method has a parameter and it requires a variable to perform the method thus its just like when your mom asks you to go out for shopping but you have arguments that you need money and a hello kitty bag to perform that task. For example : Let's say a method called a go_for_shopping requires two variables to perform its task, if we don't provide the integers it will give you an error.

void go_for_shopping(string hello_kitty_bag, int money){ return hello_kitty_bag + money; }

But when you set no parameters it will perform the task without any arguments when you call that method.

Answer 2

To be clear _onLoginButtonPressed seems to be of type void Function() and you trying to set callback to some widget (we have no full snippet - so I'm trying to guess)

Functions are objects in Dart - you can pass function as argument and call it later

1. This _onLoginButtonPressed returns Function object - you not calling this function, you just send it elsewhere

2. When this _onLoginButtonPressed() calls that function and returns void(nothing)

In second case you will get error when you try use result

This expression has a type of ‘void’ so its value can’t be used.

Answer 3

in this case, its not whether one of the methods has a parameter or not but rather if you put the parenthesis or not. When you use the parenthesis in a method, you are evoking it. (running the function).

state is! LoginInProgress ? _onLoginButtonPressed(): null, << runs the function

state is! LoginInProgress ? _onLoginButtonPressed : null, << doesn't run the function

to make it more clear:

dynamic storeFunction = _onLoginButtonPressed; << stores the function on the variable storeFunction

dynamic storeFunctionResult = _onLoginButtonPressed(); << runs the function and stores the result returned by it on the storeFunctionResult variable (if return type is not void)