Class

Introduction

Unreal Engine 4 is based around several paradigms, one at the core is Object Orientation. This describes Classes and Objects as basic building blocks, especially in relation to the C++ programming language which the Unreal Engine is built ontop of as its foundation.

Inheritance

In Class Based Programming (a style of OOP) inheritance occurs through defining classes of the objects you intend to use.

Example 1

As a basic example YourObject is declared as a child of Object.

• Object
  • YourObject

YourObject derives its functionality from its parent. Lets say Object has the function (method) GetClass() your Object will also have this function since its implemented in its parent.

• Object::GetClass()
  • YourObject::GetClass()

Example 2

A more complex example might be two classes extending different Objects.

• Object
  • YourObjectA
  • ActorComponent::DestroyComponent()
    • YourObjectB::DestroyComponent()

In the above only your Object B can call the DestroyComponent method since that function is implemented in the ActorComponent the child of Object.
Where your Object A does not have the DestroyComponent method, it only has the methods defined in its parent Object.
It is also important to note that since ActorComponent is a child of Object it (along with your Object B) inherits all methods from the parent but none from your Object A because it's not a direct descendant in the Class Hierarchy (or Tree).

Property System

An object can be a variable, a data structure, a function, or a method, which is why all types in the Property System start with the U prefix.

Blueprint

Blueprint is used to create classes from within Unreal Editor, these are Asset Types as well as referring to the Graph Editor itself.

Defining Classes

As you can see from the below, all Objects defined UCLASS() require the GENERATED_BODY() macro so that property system can properly manage them.

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Objects

Prefix for any Object in Unreal Engine 4 is U however your file name should be YourObject.h

UCLASS()
class UYourObject : public UObject
{
    GENERATED_BODY()
};

Actors

Prefix for any Actor in Unreal Engine 4 is A however your file name should be YourActor.h

UCLASS()
class AYourActor : public AActor
{
    GENERATED_BODY()
};

Constructor

A special type of member function which is called when we instantiate an Object (or Actor) of this Class. This code is typically place at the top of the YourActor.cpp

AYourActor::AYourActor()
{
    /* Your Actors Constructor - Not to be confused with Construction Script in Blueprint */
}

Classes with a GENERATED_BODY() will recieve a default constructor (the above), you may define your own constructor methods in the YourActor.h;

UCLASS()
class AYourActor : public AActor
{
    GENERATED_BODY()

    AYourActor(const FObjectInitializer& ObjectInitializer);
};

This allows you to access the ObjectInitializer in your constructor.

Constructor Helpers

Destructor

Abstract Class

This is a special type of Class which cannot be instantiated as an object, methods are called directly on the class itself.

Class Literal

• class
• TSubclassOf

static ConstructorHelpers::FClassFinder PlayerPawnClassFinder(TEXT("/Game/Blueprints/MyCharacter"));
DefaultPawnClass = PlayerPawnClassFinder.Class;

Static Classes

Instantiating Objects

Object in this case refers to a particular instance of a class that is created.

Creation

UStaticMeshComponent* Mesh = NewObject (Owner);

In this example we can see the a new object Mesh is created from the class UStaticMeshComponent.

Default Objects

see Component

Destruction

Garbage Collection

See Memory Management

Polymorphism

Object Literal

• Find Object
• Referencing Assets

Further Reading

Epic Official Documentation

• Class Creation
• Gameplay Classes
• Objects - Explanations of the basic gameplay elements, Actors and Objects
• Unreal Object Handling - Overview of the features of the UObject system

Wikipedia

• Class
• Class Simple
• Object

Others

• Classes and Objects - w3schools