Interface Demo for Unreal Engine 4

InterfaceDemo.h

#pragma once

#include "CoreMinimal.h"
#include "UObject/Interface.h"
#include "InterfaceDemo.generated.h"

UINTERFACE()
class UBaseInterface : public UInterface
{
	GENERATED_BODY()
};

class IBaseInterface
{
	GENERATED_BODY()

public:

	// Will cause a compile error
	// UPROPERTY()
	// int32 Variable;
	
	// Will compile, but should be avoided
	// int32 SomeOtherVariable;
};

UINTERFACE(meta=(CannotImplementInterfaceInBlueprint))
class UNativeInterface : public UInterface
{
	GENERATED_BODY()
};

class INativeInterface
{
	GENERATED_BODY()

public:

	virtual void DefinedVirtualFunction() {};
	virtual void PureVirtualFunction() = 0;

	UFUNCTION(BlueprintCallable)
	virtual void ExposedVirtualFunction() {}
};

UINTERFACE(/* Blueprintable */)
class UMixedInterface : public UInterface
{
	GENERATED_BODY()
};

class IMixedInterface
{
	GENERATED_BODY()

public:

	UFUNCTION(BlueprintImplementableEvent, BlueprintCallable)
	void BPFunction();

	UFUNCTION(BlueprintNativeEvent, BlueprintCallable)
	void BPNativeFunction();

	// Will cause a compile error
	// UFUNCTION(BlueprintCallable)
	// virtual void ExposedVirtualFunction() {}

};

InterfaceImplementation.h

#pragma once

#include "CoreMinimal.h"
#include "UObject/Object.h"
#include "InterfaceDemo.h"
#include "InterfaceImplementation.generated.h"

UCLASS()
class UImplementor 
	: public UObject
	, public INativeInterface
	, public IMixedInterface
{
	GENERATED_BODY()

public:

	void DefinedVirtualFunction() override 
	{
		// do something
	};

	void PureVirtualFunction() override
	{
		// do something else
	}

	void BPNativeFunction_Implementation() override
	{
		// do something native
	}
};