自定义资源的定义

在UE4里存在大量的内置资源, 例如UStaticMesh(镜头),USkeletalMesh(骨骼网格), UMaterial(材质), UMaterialInstance(材质实例), UTexture(纹理)，如下所示.

这些资源在C++层面都是继承UObject形成的对象，如UStaticMesh

我们由于项目需求得定义属于自己的资源，扩展出我们的自定义资源。

(1)继承UObject，创建我们资源对象，注意这个自定义的UMyObject可位于Runtime模块或者Editor模块,取决于你的需求

UCLASS()
class MYTEST_API UMyObject : public UObject
{
	GENERATED_BODY()

public:
	UPROPERTY(EditAnywhere)
		int A;
};

(2)创建我们的UObject对应的Factory, 注意UMyObjectFactory必须位于Editor模块

#include "CoreMinimal.h"
#include "Factories/Factory.h"
#include "MyObjectFactory.generated.h"

/**
 * 
 */
UCLASS()
class MYTEST_API UMyObjectFactory : public UFactory
{
	GENERATED_BODY()

public:
	UMyObjectFactory();

	virtual UObject* FactoryCreateNew(UClass* InClass, UObject* InParent, FName InName, EObjectFlags Flags, UObject* Context, FFeedbackContext* Warn);
	
};

#include "MyObjectFactory.h"
#include "MyObject.h"

UMyObjectFactory::UMyObjectFactory()
{
	bCreateNew = true;
	bEditAfterNew = true;
	SupportedClass = UMyObject::StaticClass();
}

UObject* UMyObjectFactory::FactoryCreateNew(UClass* InClass, UObject* InParent, 
	FName InName, EObjectFlags Flags, UObject* Context, FFeedbackContext* Warn)
{
	UMyObject* MyObject = NewObject<UMyObject>(InParent, InName, Flags | RF_Transactional);
	return MyObject;
}

在修改配置模块.cs文件，添加 “UnrealEd”

之后就可以在编辑器创建我们的自定义资源了

自定义资源的类别和筛选功能

按照上面的步骤得到的资源默认在 “Miscellaneous”

并且筛选类别无法找到该资源

下面我们通过注册自定义Category, 并且将我们自定义的资源资源放在自定义Category上

(1)继承FAssetTypeActions_Base

#include "AssetTypeActions_Base.h"


class FMyObjectTypeAction : public FAssetTypeActions_Base
{
public:
	virtual FText GetName() const override;
	virtual uint32 GetCategories() override;
	virtual FColor GetTypeColor() const override;
	virtual FText GetAssetDescription(const FAssetData& AssetData) const override;
	virtual UClass* GetSupportedClass() const override;
};

#include "MyObject.h"


FText FMyObjectTypeAction::GetName() const
{
	return FText::FromString("MyObject");
}

uint32 FMyObjectTypeAction::GetCategories()
{
	return MyCustomCategory;
}

FColor FMyObjectTypeAction::GetTypeColor() const
{
	return FColor(255, 0, 0, 255);
}

FText FMyObjectTypeAction::GetAssetDescription(const FAssetData& AssetData) const
{
	return FText::FromString("MyObjectDes");
}

UClass* FMyObjectTypeAction::GetSupportedClass() const
{
	return UMyObject::StaticClass();
}

（2）在模块StartupModule里注册自定义类别EAssetTypeCategories::Type，EAssetTypeCategories::Type为筛选资源的类别, 并且注册AssetTypeActions

// The list of categories for Asset Type Actions and UFactory subclasses
namespace EAssetTypeCategories
{
	enum Type
	{
		None = 0,
		Basic = 1 << 0,
		Animation = 1 << 1,
		MaterialsAndTextures = 1 << 2,
		Sounds = 1 << 3,
		Physics = 1 << 4,
		UI = 1 << 5,
		Misc = 1 << 6,
		Gameplay = 1 << 7,
		Blueprint = 1 << 8,
		Media = 1 << 9,

		// Items below this will be allocated at runtime via RegisterAdvancedAssetCategory
		FirstUser = 1 << 10,
		LastUser = 1 << 31,
		// Last allowed value is 1 << 31
	};
}

	IAssetTools& AssetTools = FModuleManager::Get().GetModuleChecked<FAssetToolsModule>("AssetTools").Get();
	MyCustomCategory = AssetTools.RegisterAdvancedAssetCategory(FName("MyCustom"), FText::FromString("MyCustom"));

	AssetTools.RegisterAssetTypeActions(MakeShareable(new FMyObjectTypeAction));

记得卸载模块

	if (FModuleManager::Get().IsModuleLoaded("AssetTools"))
	{
		IAssetTools& AssetTools = FModuleManager::Get().GetModuleChecked<FAssetToolsModule>("AssetTools").Get();
		AssetTools.UnregisterAssetTypeActions(MakeShareable(new FMyObjectTypeAction));
	}

这样我们的自定义资源(MyObject)出现在我们的自定义类别(MyCustom)里.

筛选功能也具备了

自定义资源的读取和修改

我们在编辑器创建一个自定义资源对象，如何在C++代码里修改它呢？怎么读取并且修改呢，其实就是之前文章说过的LoadObject. 不过修改属性之钱得调用Modify

自定义资源的生成

	const FString PackageName = "/Game/Test";
	const FString ObjectName = "Test";
	UPackage* Package = CreatePackage(NULL, *PackageName);
	UMyObject* MyObject = NewObject<UMyObject>(Package, *ObjectName, RF_Standalone | RF_Public);
	MyObject->A = 100;
	MyObject->PostEditChange();
	MyObject->MarkPackageDirty();
	FAssetRegistryModule::AssetCreated(MyObject);

调用资源创建器创建资源

	FAssetToolsModule& AssetToolsModule = FModuleManager::GetModuleChecked<FAssetToolsModule>("AssetTools");
	UMyObjectFactory* FactoryInstance = NewObject<UMyObjectFactory>();
	UObject* NewAsset = AssetToolsModule.Get().CreateAssetWithDialog(UMyObject::StaticClass(), FactoryInstance);
	if (NewAsset)
	{
		UMyObject* MyObject = Cast<UMyObject>(NewAsset);
		if (MyObject)
		{
			MyObject->Modify();
			MyObject->A = 100;
		}
	}

参考资料

[1] https://answers.unrealengine.com/questions/337715/custom-asset-category.html

[2] https://forums.unrealengine.com/development-discussion/c-gameplay-programming/1414667-is-it-possible-to-add-custom-asset-category-for-custom-data-asset