C#•10mo ago

✅ Get delegate from event

I got class

public static class Events
{
  public static PlayerEvents Player { get; } = new PlayerEvents();
}

public static class Events
{
  public static PlayerEvents Player { get; } = new PlayerEvents();
}

and PlayerEvents class contains

public class PlayerEvents
{
    public event Event<PlayerLeftServer> Leaving;

    public event Event<PlayerLeftServer> Left;
}

public class PlayerEvents
{
    public event Event<PlayerLeftServer> Leaving;

    public event Event<PlayerLeftServer> Left;
}

I want to get delegate from Leaving/Left event but seems like while trying to get value its null? idk

            foreach (var property in typeof(Events).GetProperties(BindingFlags.Public | BindingFlags.Static))
            {
                foreach (var ev in property.PropertyType.GetEvents())
                {
                    FieldInfo evField = property.PropertyType.GetField(ev.Name, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.GetField);

                    // GetValue returns null
                    Debug.Log(evField.GetValue(property.GetValue(null, null)));
                }
            }

            foreach (var property in typeof(Events).GetProperties(BindingFlags.Public | BindingFlags.Static))
            {
                foreach (var ev in property.PropertyType.GetEvents())
                {
                    FieldInfo evField = property.PropertyType.GetField(ev.Name, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.GetField);

                    // GetValue returns null
                    Debug.Log(evField.GetValue(property.GetValue(null, null)));
                }
            }

14 Replies

Killers0992OP•10mo ago

Someone will ask why I didnt add like method in PlayerEvents class which just for example Uses Leaving?.Invoke(args) what I want to create single static method for calling any event with that argument without needing to create x amount of methods just for calling these events something like

static void Invoke<T>(T ev) where T : BaseEvent
{
    /// Checks dictionary and gets that specific delegate and uses Invoke(ev);
}

static void Invoke<T>(T ev) where T : BaseEvent
{
    /// Checks dictionary and gets that specific delegate and uses Invoke(ev);
}

cap5lut•10mo ago

when u add/remove an event listener to the event, the underlying event delegate will change, if its value is null, it means that there is currently no listener listening on the event if u look at the lowered code of

public class C {
    public event Action<int> A;
}

public class C {
    public event Action<int> A;
}

this becomes more obvious:

public class C
{
    [CompilerGenerated]
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private Action<int> m_A;

    public event Action<int> A
    {
        [CompilerGenerated]
        add
        {
            Action<int> action = this.A;
            while (true)
            {
                Action<int> action2 = action;
                Action<int> value2 = (Action<int>)Delegate.Combine(action2, value);
                action = Interlocked.CompareExchange(ref this.A, value2, action2);
                if ((object)action == action2)
                {
                    break;
                }
            }
        }
        [CompilerGenerated]
        remove
        {
            Action<int> action = this.A;
            while (true)
            {
                Action<int> action2 = action;
                Action<int> value2 = (Action<int>)Delegate.Remove(action2, value);
                action = Interlocked.CompareExchange(ref this.A, value2, action2);
                if ((object)action == action2)
                {
                    break;
                }
            }
        }
    }
}

public class C
{
    [CompilerGenerated]
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private Action<int> m_A;

    public event Action<int> A
    {
        [CompilerGenerated]
        add
        {
            Action<int> action = this.A;
            while (true)
            {
                Action<int> action2 = action;
                Action<int> value2 = (Action<int>)Delegate.Combine(action2, value);
                action = Interlocked.CompareExchange(ref this.A, value2, action2);
                if ((object)action == action2)
                {
                    break;
                }
            }
        }
        [CompilerGenerated]
        remove
        {
            Action<int> action = this.A;
            while (true)
            {
                Action<int> action2 = action;
                Action<int> value2 = (Action<int>)Delegate.Remove(action2, value);
                action = Interlocked.CompareExchange(ref this.A, value2, action2);
                if ((object)action == action2)
                {
                    break;
                }
            }
        }
    }
}

and if u look at the Delegate.Remove(Delegate, Delegate) method's documentation, it says:

A new delegate with an invocation list formed by taking the invocation list of source and removing the last occurrence of the invocation list of value, if the invocation list of value is found within the invocation list of source. Returns source if value is null or if the invocation list of value is not found within the invocation list of source. Returns a null reference if the invocation list of value is equal to the invocation list of source or if source is a null reference.

the highlighted code basically means if the invocation list result would be empty afterwards, it returns null

Killers0992OP•10mo ago

seems like without doing something like this its not possible really to easily create single method to invoke x event?

cap5lut•10mo ago

yeah, seems like the only way. note that usually events are only invocable by the owning type and not from "the outside". so u would have to write these InvokeLeft and alike methods anyway if u want to make that possible

Killers0992OP•10mo ago

idk if this method is way slower than last one