FormFieldSetter<T>  typedef 
    Null safety
 
Signature for being notified when a form field changes value.
Used by FormField.onSaved.
Implementation
typedef FormFieldSetter<T> = void Function(T? newValue);Signature for being notified when a form field changes value.
Used by FormField.onSaved.
typedef FormFieldSetter<T> = void Function(T? newValue);