87 lines
3.9 KiB
Markdown
87 lines
3.9 KiB
Markdown
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# Untracked
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- **功能描述：** 使得TSoftObjectPtr和FSoftObjectPath的软对象引用类型的属性，不跟踪记录资产的 。
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- **使用位置：** UPROPERTY
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- **引擎模块：** Object Property
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- **元数据类型：** bool
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- **限制类型：** TSoftObjectPtr，FSoftObjectPath
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- **常用程度：** ★
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使得TSoftObjectPtr和FSoftObjectPath的软对象引用类型的属性，不跟踪记录资产的 。
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一般默认情况，属性上的软对象引用也是会产生资产的引用依赖，虽然在Load本身的时候，不会像硬引用一样也去加载其他软引用对象。但是因为引用关系依然存在，因此在cook的时候，或者资产重定向的时候都会去检查这些软引用对象，确保其也会被cook进去，或者正常的处理。
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而当你想在属性上记录“引用”一些资产，以便之后加载使用，但是又不想产生真正的资产引用依赖，这个时候就可以用untracked。源码中应用的不多，这是比较稀少的情况下。
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和transient标记的区别是，transient属性在序列化的时候也不会序列化，因为其ctrl+S保存后重启编辑器会丢失值。transient属性既不产生资产引用关系也序列化保存值，Untracked属性会序列化保存值但不产生资产引用关系。
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## 测试代码：
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```cpp
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyProperty_Soft :public UDataAsset
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{
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GENERATED_BODY()
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public:
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UPROPERTY(EditAnywhere, BlueprintReadWrite)
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TSoftObjectPtr<UStaticMesh> MyStaticMesh;
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UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (Untracked))
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TSoftObjectPtr<UStaticMesh> MyStaticMeshUntracked;
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UPROPERTY(EditAnywhere, BlueprintReadWrite)
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FSoftObjectPath MySoftMesh;
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UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (Untracked))
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FSoftObjectPath MySoftMeshUntracked;
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UPROPERTY(EditAnywhere, BlueprintReadWrite, Transient)
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TSoftObjectPtr<UStaticMesh> MyStaticMeshTransient;
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};
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```
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## 蓝图效果：
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在蓝图中建立一个UMyProperty_Soft DataAsset资产，然后设置其属性值。然后查看其引用的资源，会发现Untracked的属性，其设置的资产并没有出现在引用关系中。当然Transient的属性也不在引用关系中。
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## 原理：
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Untracked元数据，会设置为ESoftObjectPathCollectType::NeverCollect的选项。继续搜索会发现带有NeverCollect的FSoftObjectPath，其上面的资产package 不会被算到资产引用里，从而不会带到upackage Import表里。源码中有多处地方带有这个NeverCollect 的类似判断。
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```cpp
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bool FSoftObjectPathThreadContext::GetSerializationOptions(FName& OutPackageName, FName& OutPropertyName, ESoftObjectPathCollectType& OutCollectType, ESoftObjectPathSerializeType& OutSerializeType, FArchive* Archive) const
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{
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#if WITH_EDITOR
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bEditorOnly = Archive->IsEditorOnlyPropertyOnTheStack();
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static FName UntrackedName = TEXT("Untracked");
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if (CurrentProperty && CurrentProperty->GetOwnerProperty()->HasMetaData(UntrackedName))
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{
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// Property has the Untracked metadata, so set to never collect references if it's higher than NeverCollect
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CurrentCollectType = FMath::Min(ESoftObjectPathCollectType::NeverCollect, CurrentCollectType);
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}
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#endif
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}
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FArchive& FImportExportCollector::operator<<(FSoftObjectPath& Value)
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{
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FName CurrentPackage;
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FName PropertyName;
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ESoftObjectPathCollectType CollectType;
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ESoftObjectPathSerializeType SerializeType;
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FSoftObjectPathThreadContext& ThreadContext = FSoftObjectPathThreadContext::Get();
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ThreadContext.GetSerializationOptions(CurrentPackage, PropertyName, CollectType, SerializeType, this);
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if (CollectType != ESoftObjectPathCollectType::NeverCollect && CollectType != ESoftObjectPathCollectType::NonPackage)
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{
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FName PackageName = Value.GetLongPackageFName();
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if (PackageName != RootPackageName && !PackageName.IsNone())
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{
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AddImport(Value, CollectType);
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}
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}
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return *this;
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}
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```
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