What is [NotifyPropertyChangedInvocator] in C# whe

Question

I see two types of implementation of INotifyPropertyChanged

• The first one:

  public abstract class ViewModelBase : INotifyPropertyChanged
  {
      public event PropertyChangedEventHandler PropertyChanged;
  
      protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
      {
          PropertyChangedEventHandler handler = PropertyChanged;
          if (handler != null)
          {
              handler(this, new PropertyChangedEventArgs(propertyName));
          }
      }
  }
  

• The second one:

  public abstract class ViewModelBase : INotifyPropertyChanged
  {
      public event PropertyChangedEventHandler PropertyChanged;
  
      [NotifyPropertyChangedInvocator]
      protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
      {
          PropertyChangedEventHandler handler = PropertyChanged;
          if (handler != null)
          {
              handler(this, new PropertyChangedEventArgs(propertyName));
          }
      }
  }
  

In 2nd one you see there is an extra attribute [NotifyPropertyChangedInvocator] on the method OnPropertyChanged

In my case both behaves same but what, why and when to use this [NotifyPropertyChangedInvocator], what are benefits of this? I've searched on internet but couldn't find any good answer.

Answer 1

It is a Resharper attribute from their Annotations - designed to give you warning then your code looks suspicious :)
Consider this:

public class Foo : INotifyPropertyChanged 
{
     public event PropertyChangedEventHandler PropertyChanged;

     [NotifyPropertyChangedInvocator]
     protected virtual void NotifyChanged(string propertyName) { ... }

     private string _name;
     public string Name {
       get { return _name; }
       set { 
             _name = value; 
             NotifyChanged("LastName");//<-- warning here
           } 
     }
   }

With the [NotifyPropertyChangedInvocator] attribut on the NotifyChanged method Resharper will give you a warning, that you are invoking the method with a (presumably) wrong value.

Because Resharper now knows that method should be called to make change notification, it will help you convert normal properties into properties with change notification:
Converting it into this:

public string Name
{
  get { return _name; }
  set
  {
    if (value == _name) return;
    _name = value;
    NotifyChange("Name");
  }
}

This example is from the documentation on the [NotifyPropertyChangedInvocator] attribute found here:

Answer 2

The NotifyPropertyChangedInvocator is a Resharper feature.

You can simply remove it from your code in order for it to work

Similar question been asked here:

does anyone know how to get the [NotifyPropertyChangedInvocator]