Raise an event of a class from a different class in C#

Question

I have a class, EventContainer.cs, which contains an event, say:

public event EventHandler AfterSearch;

I have another class, EventRaiser.c

Answer 1

I stumbled across this problem as well, because i was experimenting with calling PropertyChanged events from outside. So you dont have to implement everything in every class. The solution from halorty wouldn't work using interfaces.

I found a solution working using heavy reflection. It is surely slow and is breaking the principle that events should only be called from inside a class. But it is interesting to find a generic solution to this problem....

It works because every event is a list of invocation methods being called. So we can get the invocation list and call every listener attached to that event by our own.

Here you go....

class Program
{
  static void Main(string[] args)
  {
    var instance = new TestPropertyChanged();
    instance.PropertyChanged += PropertyChanged;

    instance.RaiseEvent(nameof(INotifyPropertyChanged.PropertyChanged), new PropertyChangedEventArgs("Hi There from anywhere"));
    Console.ReadLine();
  }

  private static void PropertyChanged(object sender, PropertyChangedEventArgs e)
  {
    Console.WriteLine(e.PropertyName);
  }
}

public static class PropertyRaiser
{
  private static readonly BindingFlags staticFlags = BindingFlags.Instance | BindingFlags.NonPublic;

  public static void RaiseEvent(this object instance, string eventName, EventArgs e)
  {
    var type = instance.GetType();
    var eventField = type.GetField(eventName, staticFlags);
    if (eventField == null)
      throw new Exception($"Event with name {eventName} could not be found.");
    var multicastDelegate = eventField.GetValue(instance) as MulticastDelegate;
    if (multicastDelegate == null)
      return;

    var invocationList = multicastDelegate.GetInvocationList();

    foreach (var invocationMethod in invocationList)
      invocationMethod.DynamicInvoke(new[] {instance, e});
  }
}

public class TestPropertyChanged : INotifyPropertyChanged
{
  public event PropertyChangedEventHandler PropertyChanged;
}