Example FieldNotify Classes

ExampleFieldNotifyObject.cpp

#include "ExampleFieldNotifyObject.h"

void UExampleFieldNotifyObject::SetMyValue(int32 InValue)
{
	if (MyValue != InValue)
	{
		MyValue = InValue;
        // FFieldNotificationClassDescriptor::MyValue is auto-generated by UHT
		BroadcastFieldValueChanged(FFieldNotificationClassDescriptor::MyValue);
	}
}

ExampleFieldNotifyObject.h

#pragma once

#include "CoreMinimal.h"
#include "FieldNotifyObjectBase.h"
#include "FieldNotification/FieldNotificationDeclaration.h"
#include "ExampleFieldNotifyObject.generated.h"

UCLASS()
class GYGAX_API UExampleFieldNotifyObject : public UFieldNotifyObjectBase
{
	GENERATED_BODY()

public:
	void SetMyValue(int32 InValue);
	
protected:
	// All that's needed to use Field Notification now is the `FieldNotify` specifier
	UPROPERTY(BlueprintReadOnly, Transient, FieldNotify)
	int32 MyValue = 0;
};

FieldNotifyObjectBase.cpp

#include "FieldNotifyObjectBase.h"

FDelegateHandle UFieldNotifyObjectBase::AddFieldValueChangedDelegate(UE::FieldNotification::FFieldId InFieldId, FFieldValueChangedDelegate InNewDelegate)
{
	FDelegateHandle Result;
	if (InFieldId.IsValid())
	{
		Result = FieldNotifyDelegates.Add(this, InFieldId, MoveTemp(InNewDelegate));
		if (Result.IsValid())
		{
			EnabledFieldNotifications.PadToNum(InFieldId.GetIndex() + 1, false);
			EnabledFieldNotifications[InFieldId.GetIndex()] = true;
		}
	}
	return Result;
}

bool UFieldNotifyObjectBase::RemoveFieldValueChangedDelegate(UE::FieldNotification::FFieldId InFieldId, FDelegateHandle InHandle)
{
	bool bResult = false;
	if (InFieldId.IsValid() && InHandle.IsValid() && EnabledFieldNotifications.IsValidIndex(InFieldId.GetIndex()) && EnabledFieldNotifications[InFieldId.GetIndex()])
	{
		const UE::FieldNotification::FFieldMulticastDelegate::FRemoveFromResult RemoveResult = FieldNotifyDelegates.RemoveFrom(this, InFieldId, InHandle);
		bResult = RemoveResult.bRemoved;
		EnabledFieldNotifications[InFieldId.GetIndex()] = RemoveResult.bHasOtherBoundDelegates;
	}
	return bResult;
}

int32 UFieldNotifyObjectBase::RemoveAllFieldValueChangedDelegates(const void* InUserObject)
{
	int32 bResult = 0;
	if (InUserObject)
	{
		const UE::FieldNotification::FFieldMulticastDelegate::FRemoveAllResult RemoveResult = FieldNotifyDelegates.RemoveAll(this, InUserObject);
		bResult = RemoveResult.RemoveCount;
		EnabledFieldNotifications = RemoveResult.HasFields;
	}
	return bResult;
}

int32 UFieldNotifyObjectBase::RemoveAllFieldValueChangedDelegates(UE::FieldNotification::FFieldId InFieldId, const void* InUserObject)
{
	int32 bResult = 0;
	if (InUserObject)
	{
		const UE::FieldNotification::FFieldMulticastDelegate::FRemoveAllResult RemoveResult = FieldNotifyDelegates.RemoveAll(this, InFieldId, InUserObject);
		bResult = RemoveResult.RemoveCount;
		EnabledFieldNotifications = RemoveResult.HasFields;
	}
	return bResult;
}

const UE::FieldNotification::IClassDescriptor& UFieldNotifyObjectBase::GetFieldNotificationDescriptor() const
{
	static FFieldNotificationClassDescriptor Local;
	return Local;
}

void UFieldNotifyObjectBase::BroadcastFieldValueChanged(UE::FieldNotification::FFieldId InFieldId)
{
	if (InFieldId.IsValid() && EnabledFieldNotifications.IsValidIndex(InFieldId.GetIndex()) && EnabledFieldNotifications[InFieldId.GetIndex()])
	{
		FieldNotifyDelegates.Broadcast(this, InFieldId);
	}
}

FieldNotifyObjectBase.h

#pragma once

#include "CoreMinimal.h"
#include "FieldNotification/FieldMulticastDelegate.h"
#include "FieldNotification/IFieldValueChanged.h"
#include "UObject/Object.h"
#include "FieldNotifyObjectBase.generated.h"

UCLASS()
class MYGAME_API UFieldNotifyObjectBase : public UObject, public INotifyFieldValueChanged
{
	GENERATED_BODY()
	
public:
	struct MYGAME_API FFieldNotificationClassDescriptor : public ::UE::FieldNotification::IClassDescriptor
	{
		// OPTIONAL - Only necessary if you need to inject additional fields, for example UMVVMViewModelBase will add blueprint field notify properties
		// virtual void ForEachField(const UClass* Class, TFunctionRef<bool(UE::FieldNotification::FFieldId FielId)> Callback) const override;
	};
	
	virtual FDelegateHandle AddFieldValueChangedDelegate(UE::FieldNotification::FFieldId InFieldId, FFieldValueChangedDelegate InNewDelegate) override;
	virtual bool RemoveFieldValueChangedDelegate(UE::FieldNotification::FFieldId InFieldId, FDelegateHandle InHandle) override;
	virtual int32 RemoveAllFieldValueChangedDelegates(const void* InUserObject) override;
	virtual int32 RemoveAllFieldValueChangedDelegates(UE::FieldNotification::FFieldId InFieldId, const void* InUserObject) override;
	virtual const UE::FieldNotification::IClassDescriptor& GetFieldNotificationDescriptor() const override;
	
protected:
	void BroadcastFieldValueChanged(UE::FieldNotification::FFieldId InFieldId);
	
private:
	UE::FieldNotification::FFieldMulticastDelegate FieldNotifyDelegates;
	TBitArray<> EnabledFieldNotifications;
};