---
title: Objects in Unreal Engine
source: https://dev.epicgames.com/documentation/en-us/unreal-engine/objects-in-unreal-engine
version: Unreal Engine 5.8 Documentation
fetched: 2026-10-11
note: 原文摘录（英文），供 wiki 引用；非全文
---

# Objects in Unreal Engine

- The base class for objects in Unreal is `UObject`. The `UCLASS` macro can be used to tag classes derived from `UObject` so that the UObject handling system is aware of them.
- The UCLASS macro gives the `UObject` a reference to a `UCLASS` that describes its Unreal-based type. Each `UCLASS` maintains one Object called the Class Default Object (CDO). The CDO is essentially a default 'template' Object, generated by the class constructor and unmodified thereafter. ... The UCLASS for an Object instance can be accessed at any time using `GetClass()`.
- A UObject class can include native-only properties that are not marked for reflection ... However, only functions and properties that are marked with specifier macros will get listed within their corresponding UCLASS.
- UObjects do not support constructor arguments. ... the engine calls their default constructor. If there is no default constructor, your UObject will not compile.
- UObject constructors should be lightweight and only used to set up default values and subobjects ... For Actors and Actor Components, initialization functionality should be put into the `BeginPlay()` method instead.
- UObjects should only be constructed using NewObject at runtime, or CreateDefaultSubobject for constructors. ... UObjects should never use the `new` operator. All UObjects are memory managed by Unreal Engine and garbage collected.
- Functionality: Garbage collection; Reference updating; Reflection; Serialization; Automatic updating of default property changes; Automatic property initialization; Automatic editor integration; Type information available at runtime; Network replication. Most of these benefits apply to UStructs ... UStructs are considered value types and are not garbage collected.
- The Unreal Header Tool: a preprocessing step needs to be run on the header files for these types to collate the information it needs. This preprocessing step is performed by the UnrealHeaderTool, or UHT.
- `#include "MyObject.generated.h"` is expected to be the last `#include` directive in the file. `MYPROJECT_API` is necessary if MyProject wishes to expose the UMyObject class to other modules. `GENERATED_BODY()` ... is required for all `UCLASS` and `USTRUCT`.
- Unreal Header Tool supports a minimal set of C++. When wrapping parts of a UCLASS with custom `#ifdefs` macros, UHT will ignore macros that do not contain `WITH_EDITOR` or `WITHEDITORONLY_DATA` macros.
- Updating Objects: Actors and ActorComponents have their Tick functions called automatically when registered to do so, however, `UObjects` do not possess any built-in update ability ... can be added by inheriting from the `FTickableGameObject` class.
- Destroying Objects: handled automatically by the garbage collection system when an Object is no longer referenced. This means that no `UPROPERTY` pointers, engine containers, `TStrongObjectPtr`, or class instances should have any strong references to them. Weak Pointers have no impact on whether an Object is garbage collected or not.
- `Object->MarkPendingKill()` has been replaced with `Obj->MarkAsGarbage()` ... If `gc.PendingKillEnabled=true` then objects marked as `PendingKill` will be automatically nulled and destroyed by Garbage Collector.
- You can replace Strong pointers with weak pointers and dereference them once during a gameplay operation as garbage collection only runs between frames.
- `IsValid()` is for checking if it's null or garbage ...
- If `PendingKill()` is disabled, `MarkGarbage()` will flag to the owner of the object that it wants the object destroyed, but the object itself will not get garbage collected until all references to it are released.
- In the case of Actors, even if the Actor had `Destroy()` called on them, and they were removed from the level, then it will not be Garbage Collected until all references to it are released.
- Using `MarkPendingKill()` to force expensive objects to garbage collect will no longer work. Existing checks for nullptr should be replaced with `IsValid()` calls if you're not clearing them manually.
- Smart pointers are not intended to be used with UObjects.