[UE4]C++实现动态加载的问题：LoadClass<T>()和LoadObject<T>()

原文作者：@玄冬Wong 

 

相关内容：
C++静态加载问题：ConstructorHelpers::FClassFinder()和FObjectFinder() 

http://aigo.iteye.com/blog/2281373

C++实现动态加载UObject：StaticLoadObject()；以Texture和Material为例

http://aigo.iteye.com/blog/2268056

 

动态加载UObject和动态加载UClass分别用LoadObject<T>()，和LoadClass<T>() ，两者均在在UObjectGlobals.h中。

 

区别：

LoadObject<T>()用来加载非蓝图资源，比如动画、贴图、音效等资源；

LoadClass<T>()用来加载蓝图并获取蓝图Class，比如角色蓝图。如果要用蓝图创建对象，必须先通过LoadClass获取class，然后再通过SpawnActor生成对象。

 

LoadClass参数注意事项：

另外注意：LoadClass<T>的模版名称，不能直接写UBlueprint，例如：LoadClass<UBlueprint>是错误的，创建蓝图时选择的是什么父类，则写对应的父类名，假如是Actor，那么要写成：LoadClass<AActor>，否则无法加载成功。

路径名也必须带_C后缀（LoadObject不需要带_C后缀），例如，蓝图路径是：Blueprint'/Game/Blueprints/MyBP.MyBP'，

加后缀以后，则是：Blueprint'/Game/Blueprints/MyBP.MyBP_C'，

例子：

 

UClass* Test = LoadClass<AActor>(NULL, TEXT("Blueprint'/Game/Blueprints/MapPathBrush_BP.MapPathBrush_BP_C'"));

 

 

官方还没出文档，只能先看代码注释：

// Load an object.
template< class T > 
inline T* LoadObject( UObject* Outer, const TCHAR* Name, const TCHAR* Filename=nullptr, uint32 LoadFlags=LOAD_None, UPackageMap* Sandbox=nullptr )
{
	return (T*)StaticLoadObject( T::StaticClass(), Outer, Name, Filename, LoadFlags, Sandbox );
}

 

// Load a class object.
template< class T > 
inline UClass* LoadClass( UObject* Outer, const TCHAR* Name, const TCHAR* Filename=nullptr, uint32 LoadFlags=LOAD_None, UPackageMap* Sandbox=nullptr )
{
	return StaticLoadClass( T::StaticClass(), Outer, Name, Filename, LoadFlags, Sandbox );
}

 

/**
 * Find or load an object by string name with optional outer and filename specifications.
 * These are optional because the InName can contain all of the necessary information.
 *
 * @param ObjectClass	The class (or a superclass) of the object to be loaded.
 * @param InOuter		An optional object to narrow where to find/load the object from
 * @param InName		String name of the object. If it's not fully qualified, InOuter and/or Filename will be needed
 * @param Filename		An optional file to load from (or find in the file's package object)
 * @param LoadFlags		Flags controlling how to handle loading from disk
 * @param Sandbox		A list of packages to restrict the search for the object
 * @param bAllowObjectReconciliation	Whether to allow the object to be found via FindObject in the case of seek free loading
 *
 * @return The object that was loaded or found. NULL for a failure.
 */
COREUOBJECT_API UObject* StaticLoadObject( UClass* Class, UObject* InOuter, const TCHAR* Name, const TCHAR* Filename = NULL, uint32 LoadFlags = LOAD_None, UPackageMap* Sandbox = NULL, bool bAllowObjectReconciliation = true );
COREUOBJECT_API UClass* StaticLoadClass(UClass* BaseClass, UObject* InOuter, const TCHAR* Name, const TCHAR* Filename = NULL, uint32 LoadFlags = LOAD_None, UPackageMap* Sandbox = NULL);

 

 LoadObject参数注意事项：

 LoadObject加载例子，不需要添加后缀：

UTexture2D* Tex = LoadObject<UTexture2D>(NULL, TEXT("Texture2D'/Game/Textures/UI/tex_test001.tex_test001'"));

 

可以用LoadObject加载的文件包括：

Texture、Material、SoundWave、SoundCue、ParticlesSystem、AnimMontage、BlendSpace(1D，2D，3D)、AnimSequence、AnimBlueprint、SkeletalMesh等等。这些文件的父类都是UObject，所以也可以先加载为UObject*然后再强转为具体的类型，例如：

UObject* Obj = LoadObject<UObject>(NULL, TEXT("SkeletalMesh'/Game/MyMesh.MyMesh'"));
USkeletalMesh* MyMesh = Cast<USkeletalMesh*>(Obj);

 

  

另外有两个全局函数叫：StaticLoadObject()和StaticLoadClass()，应该是LoadObject<T>()和LoadClass<T>()的早期版本，前者需要手动强转，后者使用模版封装过，使用更方便，推荐使用后者

 

 LoadClass除了可以加载蓝图，还可以加载UObject类型的native class：

UClass* Test = LoadClass<AActor>(NULL, TEXT("Class'/Script/MyProj.MyProjCharacter'"));