How can I instantiate a UUserDefinedStruct a runtime ?

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1

In our project we have a blueprint data asset, filled by designers, that defines some key, when modified it automatically generates a UUserDefinedStruct object that correspond to a struct having key names as member variables. This blueprint struct is then used to create chooser tables.

Chooser Table uses FStructView for that, which relies on a UScriptStruct* and a memory address. I guess the UUserDefinedStruct should be passed as the script struct, but what about the memory address ?

I guess there is some kind of compilation for the UUserDefinedStruct that will provide a memoryblock similar to a classic FStruct and on which I can set values but I haven’t found how to do that, can you help me ?

2

I found the solution, which is using a FStructOnScope

Here is the code I ended up using (simplified), if that can help other people

EvaluateChooserTable(UUserDefinedStruct* ChooserTablesStruct, UChooserTable* ChooserTable)
 {
   FStructOnScope ChooserStructOnScope(ChooserTablesStructPtr); // will allow memory for a C++ style struct instance of the UUserDefinedStruct
   // loop on UUserDefinedStruct properties to fill our struct instance
   for (FProperty* Property : TFieldRange<FProperty>(ChooserTablesStruct))
   {
     // check property type and set value, in my case it was a game play tag, so the property is a struct property with a FGameplayTagContainer struct
     if (!ChooserStructProperty->IsA(FStructProperty::StaticClass()))
     {
       //unexpected
       continue;
     }
     FStructProperty* ChooserStructTypedProperty = CastFieldChecked<FStructProperty>(ChooserStructProperty);
     if (ChooserStructTypedProperty->Struct != FGameplayTagContainer::StaticStruct())
     {
       //unexpected
       continue;
     }
     FGameplayTagContainer* CurrentSlotGameplayTagContainer = ChooserStructTypedProperty->ContainerPtrToValuePtr<FGameplayTagContainer>(ChooserStructOnScope.GetStructMemory());
     CurrentSlotGameplayTagContainer->AddTag(MyTag);
   }
  
  // now evaluate the chooser table
   FChooserEvaluationContext EvaluationContext = UChooserFunctionLibrary::MakeChooserEvaluationContext();
   FStructView ChooserStructView(ChooserTablesStruct, ChooserStructOnScope.GetStructMemory());
   EvaluationContext.AddStructViewParam(ChooserStructView);
   const FInstancedStruct EvaluateChooserStruct = UChooserFunctionLibrary::MakeEvaluateChooser(ChooserTable.Get());
   UObject* ResultObject = UChooserFunctionLibrary::EvaluateObjectChooserBase(EvaluationContext, EvaluateChooserStruct, UObject::StaticClass());
 }
3

Thanks for letting us know you resolved it! And for sharing the snippet, I’m sure it will help others too.