What exactly Value setter and Value getter in flutter?

Question

I went through the documentation but didn't any get clarity on what exactly they are, need a brief explanation about ValueSetter and ValueGetter?

Explain it with an example.

  ValueSetter<T> typedef
  ValueGetter<T> typedef

Answer 1

T refers to a type parameter in ValueSetter, denoting the type of value being modified. Callback functions that accept a sole argument of type T are declared with this code.

Here's an example to illustrate the usage of ValueSetter:

typedef ValueSetter<T> = void Function(T value);

class ExampleClass {
  ValueSetter<int>? setter;

  void setValue(int value) {
    if (setter != null) {
      setter!(value);
    }
  }
}

void main() {
  final example = ExampleClass();

  example.setter = (value) {
    print('Received value: $value');
  };

  example.setValue(42); // Prints: Received value: 42
}

Using ValueSetter, a callback that accepts an integer input and does not produce any output is defined in this case. Can we locate an instance variable called ValueSetter in ExampleClass with a data type of int? that can be assigned a function matching the defined signature. If an assignable value is passed when setting the value using setValue(), the setter callback will be activated.

Let us next examine the ValueGetter typedef.

This typedef in Dart signifies a generic getter method for retrieving values from objects. This syntax outlines a function that doesn't take parameters and yields results of type T. Here's an example to illustrate the usage of ValueGetter:

typedef ValueGetter<T> = T Function();

class ExampleClass {
  ValueGetter<int>? getter;

  int getValue() {
    if (getter != null) {
      return getter!();
    }
    return 0;
  }
}

void main() {
  final example = ExampleClass();

  example.getter = () {
    return 42;
  };

  final value = example.getValue();
  print('Returned value: $value'); // Prints: Returned value: 42
}