100 lines
4.6 KiB
Markdown
100 lines
4.6 KiB
Markdown
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# NonPIEDuplicateTransient
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- **功能描述：** 在对象复制的时候，且在不是PIE的场合，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_NonPIEDuplicateTransient](../../../../Flags/EPropertyFlags/CPF_NonPIEDuplicateTransient.md)
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- **常用程度：** ★
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在对象复制的时候，且在不是PIE的场合，忽略该属性。
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- DuplicateTransient和NonPIEDuplicateTransient的区别是，前者在任何情况的对象复制时都忽略该属性，而后者在PIE的时候（也是在发生对象复制过程）依然会复制该属性，其他情况下的复制和前者行为一致。
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- PIE的时候本质就是把当前的编辑World里Actor复制一份到PIE的世界里，会触发Actor的复制。
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## 示例代码：
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准备了一份DataAsset和Actor来分别验证复制行为的不同。
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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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UCLASS(Blueprintable, BlueprintType)
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class INSIDER_API AMyProperty_Serialization_TestActor :public AActor
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{
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public:
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GENERATED_BODY()
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protected:
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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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UPROPERTY(EditAnywhere, BlueprintReadWrite, NonPIEDuplicateTransient)
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int32 MyInt_NonPIEDuplicateTransient = 123;
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};
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```
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## 示例效果：
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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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可以看到NonPIEDuplicateTransient并不会被复制。
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在点击PIE的时候，可以看到NonPIEDuplicateTransient这个时候却是会复制值过去了。这是因为这个时候PortFlags=PPF_DuplicateForPIE&PPF_Duplicate
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结论是用于一些Cache数据，在复制的时候并不需要序列化复制，这样可以阻止两个不同的Actor采用同一份计算后的临时数据。但是又可以在PIE的时候，让Actor各自采用自己的一份数据，因为PIE的时候，本质就是把当前的编辑World里Actor复制一份到PIE的世界里，会触发Actor的复制。
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## 原理：
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在文本导出的的时候，在不是PIE里的复制的时候，不序列化该属性。
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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 not copying for PIE and NonPIETransient is set, don't export
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if (!(PortFlags & PPF_DuplicateForPIE) && HasAnyPropertyFlags(CPF_NonPIEDuplicateTransient))
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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。但是在PIE的时候，又要继续序列化。
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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 NonPIEDuplicateTransient when duplicating, but not when we're duplicating for PIE
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if ((PropertyFlags & CPF_NonPIEDuplicateTransient) && !(Ar.GetPortFlags() & PPF_DuplicateForPIE) && (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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