89 lines
3.2 KiB
Markdown
89 lines
3.2 KiB
Markdown
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# DuplicateTransient
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- **功能描述：** 在对象复制或COPY格式导出的时候，忽略该属性。
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- **元数据类型：** bool
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- **引擎模块：** Serialization
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- **作用机制：** 在PropertyFlags中加入[CPF_DuplicateTransient](../../../../Flags/EPropertyFlags/CPF_DuplicateTransient.md)
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- **常用程度：** ★★
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在对象复制或COPY格式导出的时候，忽略该属性。
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## 示例代码：
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```cpp
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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API UMyProperty_Serialization :public UDataAsset
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{
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public:
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GENERATED_BODY()
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public:
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UPROPERTY(EditAnywhere, BlueprintReadWrite)
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int32 MyInt_Default = 123;
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//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_Transient | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(EditAnywhere, BlueprintReadWrite, Transient)
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int32 MyInt_Transient = 123;
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//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_DuplicateTransient | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(EditAnywhere, BlueprintReadWrite, DuplicateTransient)
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int32 MyInt_DuplicateTransient = 123;
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//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_NonPIEDuplicateTransient | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(EditAnywhere, BlueprintReadWrite, NonPIEDuplicateTransient)
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int32 MyInt_NonPIEDuplicateTransient = 123;
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};
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void UMyProperty_Serialization_Test::RunTest()
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{
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UMyProperty_Serialization* obj = NewObject<UMyProperty_Serialization>(GetTransientPackage());
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obj->MyInt_Default = 456;
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obj->MyInt_Transient = 456;
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obj->MyInt_DuplicateTransient = 456;
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obj->MyInt_NonPIEDuplicateTransient = 456;
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UMyProperty_Serialization* obj3= DuplicateObject<UMyProperty_Serialization>(obj,GetTransientPackage());
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}
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```
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## 示例效果：
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复制蓝图，可以看到DuplicateTransient并不会被复制
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在采用C++复制的时候：也看到MyInt_DuplicateTransient 并不会产生复制，还是123而不是456。
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## 原理：
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在文本导出的时候，如果是T3D格式，则依然会导出。如果是COPY格式，则不导出。
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```cpp
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bool FProperty::ShouldPort( uint32 PortFlags/*=0*/ ) const
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{
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// if we're copying, treat DuplicateTransient as transient
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if ((PortFlags & PPF_Copy) && HasAnyPropertyFlags(CPF_DuplicateTransient | CPF_TextExportTransient) && !(PortFlags & (PPF_ParsingDefaultProperties | PPF_IncludeTransient)))
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{
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return false;
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}
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}
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```
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在二进制序列化的时候：
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只有在PPF_Duplicate生效的时候，（DuplicateObject或者资产复制），才会跳过该属性
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```cpp
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bool FProperty::ShouldSerializeValue(FArchive& Ar) const
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{
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// Skip properties marked DuplicateTransient when duplicating
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if ((PropertyFlags & CPF_DuplicateTransient) && (Ar.GetPortFlags() & PPF_Duplicate))
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{
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return false;
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}
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}
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```
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在对资产进行Duplidate的时候，发生DuplicateAsset然后DuplicateObject，这个时候PortFlags=PPF_Duplicate，然后会触发ShouldSerializeValue进行判断。这个时候会跳过该属性
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