Is Dart/Flutter has a listener function?

Question

The listener function can listen to any parameter type(not only listener type). This has nothing related to widgets.

ex.

int a = 0;
listener((a>0)=>print("A = $a"));
a= 1; //A = 1
a= -1; //
a= 2; //A = 2

Answer 1

You can use ValueNotifier for this. It's a ChangeNotifier that is triggered when the value is replaced with something that is not equal to the old value as evaluated by the equality operator ==.

Here is a nice tutorial about this approach.