# Can't get child class instance from "OnHit" function

**URL:** <https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228>\
**Category:** Programming & Scripting\
**Tags:** unreal-engine\
**Created:** [May 2, 2019, 8:16am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228 "2019-05-02T08:16:38Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![micklo717](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@micklo717](https://forums.unrealengine.com/u/micklo717)\
**Post date:** [May 2, 2019, 8:16am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/1 "2019-05-02T08:16:38Z")

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Hello!  
I’m trying to make a function which changes action by hit object and use “OnHit” function.  
Some objects are made from [Y class] inherited “AActor” class.  
“OnHit” function has “AActor\* OtherActor” arugement, but I can’t cast “AActor\*” to [Y class]\*.  
So I can’t get information of hit object.

How should I deal with it?

Thanks for reading and sorry for my poor English!

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**Author:** ![Lardo\_Deepdelver](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Lardo\_Deepdelver](https://forums.unrealengine.com/u/Lardo_Deepdelver)\
**Post date:** [May 2, 2019, 9:07am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/2 "2019-05-02T09:07:47Z")

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if your hit object is a Y class or inherits from a Y class you should be totally able to cast to it?

You created a new actor right?  
something like

```
class AYClass : public AActor  

```

and the object you are hitting is of that type?  
and you use

```
auto* HitActorAsYClass = Cast<AYClass>(OtherActor);
if (HitActorAsYClass)
  HitActorAsYClass->DoSomething();
```

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<div class="post-metadata">

**Author:** ![micklo717](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@micklo717](https://forums.unrealengine.com/u/micklo717)\
**Post date:** [May 2, 2019, 9:45am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/3 "2019-05-02T09:45:02Z")

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Thank you for advice!

Hit object have various class. So it’s class type can be not only [Y class] but also [A class] or [B class] …etc.

It may be fine by a following way

```
auto* HitActorAsYClass = Cast<AYClass>(OtherActor);
if (HitActorAsYClass) {
   HitActorAsYClass->DoSomething();
} else {
   auto* HitActorAsAClass = Cast<AAClass>(OtherActor);
   if (HitActorAsAClass) {
      HitActorAsAClass->DoSomething();
   } else {
      auto* HitActorAsBClass = Cast<ABClass>(OtherActor);
      if (HitActorAsBClass) {
         HitActorAsBClass->DoSomething();
      } else {
         // if hit actor class is C, D, E...
      }
   } 
}

```

But it would become nested branch.  
Ideally I want to do like this (it has error)

```
auto* HitActor = Cast<OtherActor->GetClass()>(OtherActor);
HitActor->DoSomething();
```

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<div class="post-metadata">

**Author:** ![Lardo\_Deepdelver](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Lardo\_Deepdelver](https://forums.unrealengine.com/u/Lardo_Deepdelver)\
**Post date:** [May 2, 2019, 10:03am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/4 "2019-05-02T10:03:18Z")

</div>

casting can not work with runtime classes, it needs to know what to cast to at compile time

sounds like what you want to do is use an interface

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basically all your classes that should DoSomething need to implement that interface and in the hit you check if the object implements it, and if so call it

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<div class="post-metadata">

**Author:** ![micklo717](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@micklo717](https://forums.unrealengine.com/u/micklo717)\
**Post date:** [May 2, 2019, 10:07am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/5 "2019-05-02T10:07:38Z")

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Thank you for quick replay!  
I will learn it !

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<div class="post-metadata">

**Author:** ![Lardo\_Deepdelver](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Lardo\_Deepdelver](https://forums.unrealengine.com/u/Lardo_Deepdelver)\
**Post date:** [May 2, 2019, 10:13am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/6 "2019-05-02T10:13:19Z")

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if you want I can write a small example,  
just takes a little bit more time then a fast answer 😛

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<div class="post-metadata">

**Author:** ![micklo717](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@micklo717](https://forums.unrealengine.com/u/micklo717)\
**Post date:** [May 2, 2019, 10:41am UTC](https://forums.unrealengine.com/t/cant-get-child-class-instance-from-onhit-function/448228/7 "2019-05-02T10:41:14Z")

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I have to cast [OtherActor] to InterfaceClass and then, check it can be used by “not NULL”.

I think I can implement now!  
Thank you ! I spent more than 10 hours around this problem! Thank you !