# WTF: Event Signature Error: The function/event 'xxx' does not match the necessary signature - has the delegate or function/event changed?

**URL:** <https://forums.unrealengine.com/t/wtf-event-signature-error-the-function-event-xxx-does-not-match-the-necessary-signature-has-the-delegate-or-function-event-changed/502045>\
**Category:** Blueprint\
**Tags:** unreal-engine, UE4-26, CPP, Blueprint, question\
**Created:** [February 25, 2022, 10:10am UTC](https://forums.unrealengine.com/t/wtf-event-signature-error-the-function-event-xxx-does-not-match-the-necessary-signature-has-the-delegate-or-function-event-changed/502045 "2022-02-25T10:10:03Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![akaPrometh](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@akaPrometh](https://forums.unrealengine.com/u/akaPrometh)\
**Post date:** [February 25, 2022, 10:10am UTC](https://forums.unrealengine.com/t/wtf-event-signature-error-the-function-event-xxx-does-not-match-the-necessary-signature-has-the-delegate-or-function-event-changed/502045/1 "2022-02-25T10:10:04Z")

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I swear to god…  
Alright, new one:

I have a CPP event that when assigned/binded in a BP says:

> EventOnThrowGrapple\_Event Signature Error: The function/event ‘EventOnThrowGrapple\_Event’ does not match the necessary signature - has the delegate or function/event changed?

_When and only when_ it is cabled to something that executes.

Here’s what I do in images:  
How i assign:  
 ![1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/3/c/7/3c7a6bb93e4a8a54bce7ed14bc0df596a0871ddb.png)  
When its assigned and compiled (no errors so far)  
 ![2](https://d3kjluh73b9h9o.cloudfront.net/original/4X/5/c/a/5ca9b68997eec169b992eb01364b834de54c5a18.png)  
Error pops up only when I cable to (1), (2) warns nothing.

 ![3](https://d3kjluh73b9h9o.cloudfront.net/original/4X/b/8/7/b8743a84d70a45356919aaa74704cd7cecdb421b.png)

Here’s how the event is declared in cpp.

> DECLARE\_DYNAMIC\_MULTICAST\_DELEGATE\_OneParam(FEventDelegate\_AGrapplinHook\_OnThrowGrapple, AGrapplingHook\*, self);
> 
> UCLASS(Blueprintable)  
> class TPSMPPG\_API AGrapplingHook : public AActor  
> {  
> GENERATED\_BODY()
> 
> public:   
> AGrapplingHook();
> 
> /_---------------------------------_/  
> /_\>\>\_\_\_\_\_\_\_\_\_\_ EVENTS \_\_\_\_\_\_\_\_\_\_\<\<_/  
> UPROPERTY(BlueprintAssignable, Category = “Event Suscribers”)  
> FEventDelegate\_AGrapplinHook\_OnThrowGrapple EventOnThrowGrapple;
> 
> (more stuff)  
> }

For the love of god, what am i doing wrong?  
Thanks

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<div class="post-metadata">

**Author:** ![akaPrometh](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@akaPrometh](https://forums.unrealengine.com/u/akaPrometh)\
**Post date:** [February 25, 2022, 10:15am UTC](https://forums.unrealengine.com/t/wtf-event-signature-error-the-function-event-xxx-does-not-match-the-necessary-signature-has-the-delegate-or-function-event-changed/502045/2 "2022-02-25T10:15:48Z")

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Ok, got it. Dumb as always.  
Cannot have fields called ‘self’ in an event declaration.  
In my event I was doing:

> DECLARE\_DYNAMIC\_MULTICAST\_DELEGATE\_OneParam(FEventDelegate\_AGrapplinHook\_OnThrowGrapple, AGrapplingHook\*, 🤯 🤯_self_ 🤯🤯);

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**Author:** ![johnsu](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@johnsu](https://forums.unrealengine.com/u/johnsu)\
**Post date:** [June 3, 2024, 12:06pm UTC](https://forums.unrealengine.com/t/wtf-event-signature-error-the-function-event-xxx-does-not-match-the-necessary-signature-has-the-delegate-or-function-event-changed/502045/3 "2024-06-03T12:06:58Z")

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How did you find it out you genius!!