[C#] EventHandlerDictionary CallUtilities NullReferenceException

ApocDev · May 5, 2018, 4:48am

Spent the last hour or two trying to figure out where the following exception was coming from:

[   8347953] Error invoking callback for event __cfx_nui:ACC2DE26A37B104FBCF4FD926EDBA1B5_Clicked: System.NullReferenceException: Object reference not set to an instance of an object.
[   8347953]   at CitizenFX.Core.CallUtilities.<GetPassArguments>g__ChangeType|0_0 (System.Object value, System.Type type) [0x00000] in C:\gl\builds\aaf2d114\0\cfx\fivem\code\client\clrcore\EventHandlerDictionary.cs:112 
[   8347968]   at CitizenFX.Core.CallUtilities.GetPassArguments (System.Reflection.MethodInfo method, System.Object[] args, System.String sourceString) [0x00066] in C:\gl\builds\aaf2d114\0\cfx\fivem\code\client\clrcore\EventHandlerDictionary.cs:159 
[   8347984]   at CitizenFX.Core.EventHandlerEntry+<Invoke>d__5.MoveNext () [0x00047] in C:\gl\builds\aaf2d114\0\cfx\fivem\code\client\clrcore\EventHandlerDictionary.cs:84

Turns out the cause is here:

github.com

citizenfx/fivem/blob/master/code/client/clrcore/EventHandlerDictionary.cs#L112


            }

        }

    }



	static class CallUtilities

	{

		public static object[] GetPassArguments(MethodInfo method, object[] args, string sourceString)

		{

			List<object> passArgs = new List<object>();



			var argIdx = 0;



			object ChangeType(object value, Type type)

			{

				// FIX: Null values should be checked against. This allows greater freedom for developers in more "complex" cases.

				// (Eg; passing "null" as a string value to an event invocation, rather than forcing string.Empty)

				if (ReferenceEquals(value, null))

					return null;



				if (type.IsAssignableFrom(value.GetType()))

				{

Specifically in my case, I was sending NUI updates (from JS -> C#) with a “null” message, which should be completely acceptable (for instance, ‘Click’ events that are tied to the event name, not some arguments passed back to the C# client). Simply checking for null, and passing it as null should fix this issue all together.

We shouldn’t be forced to make sure no argument is non-null (which currently is the case, and severely hinders some events)