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TMap with Key/Value UserWidget pointers lose references on Compile

I have a UserWidget subclass with a TMap UPROPERTY where the key and value are both UUserWidget pointers (ie TMap). After creating a BP instance of my widget, the inspector lets me properly assign to the map without issue, showing the correct available widgets in the Hierarchy. If I save the Widget in the editor, those values persist. However, if I Compile the blueprint, I'll lose the values every time, and all the Map entries will be empty.

Any ideas?

Product Version: UE 4.19
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asked Aug 06 '18 at 05:50 PM in C++ Programming

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I'm afraid you can not use UUserWidgets as keys, you could try to generate a unique ID as your key and the value could contain a struct holding your pair (or even TPair).

To define your own keys what you normally do is to define how to compare your keys calsses and create a MapKeyFunction that the TMap will use to compare one to another.

The following is an example that you could follow:

 #include "Engine/EngineTypes.h"

 template<typename ValueType>
 struct TMyClassMapKeyFuncs : TDefaultMapKeyFuncs<UMyClass, ValueType, false>
     static FORCEINLINE bool Matches(UMyClass A, UMyClass B)
         return A == B; // Do your own compare here!
     static FORCEINLINE uint32 GetKeyHash(UMyClass Key)
         return ::GetTypeHash(Key);
 TMap<UMyClass, UUserWidget, FDefaultSetAllocator, TMyClassMapKeyFuncs<UUserWidget>> MyTMap;

The code above is written out of my head so it might need some love ^^

Cheers, Moss

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answered Aug 06 '18 at 10:00 PM

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