How to subscribe to an event?

Question

C++ / C#

Hitch with syntax in +=

public interface IContentState {
  public EventCallback<IContentState> OnStateChanged { get; set; }
}

public class Parent : IContentState {
  public EventCallback<IContentState> OnStateChanged { get; set; }
  private async Task StateChangedInvoke() {	
    await OnStateChanged.InvokeAsync(this);
  }
}
public class Child() {
  public void RegisterContent(IContentState contentState) {
    ContentState.OnStateChanged += OnContentStateChanged;
  }	
  protected void OnContentStateChanged(IContentState contentState) {
    // do
  }
}

Answer 1

You do not have an event in IContentState, but just a delegate.
Try to write

public event EventCallback<IContentState> StateChanged;

PS: it is customary to call events without the prefix On