7.0 KiB
7.0 KiB
Transient
- 功能描述： 不序列化该属性，该属性初始化时候会被0填充。
- 元数据类型： bool
- 引擎模块： Serialization
- 作用机制： 在PropertyFlags中加入CPF_Transient
- 常用程度：★★★★★
序列化的时候略过该属性，用0来填充默认值。
二进制和文本都不序列化该属性。
一般用于一些临时中间变量或计算后的结果变量。
示例代码：
UCLASS(Blueprintable, BlueprintType)
class INSIDER_API UMyProperty_Serialization :public UDataAsset
{
public:
GENERATED_BODY()
public:
UPROPERTY(EditAnywhere, BlueprintReadWrite)
int32 MyInt_Default = 123;
//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_Transient | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
UPROPERTY(EditAnywhere, BlueprintReadWrite, Transient)
int32 MyInt_Transient = 123;
//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_DuplicateTransient | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
UPROPERTY(EditAnywhere, BlueprintReadWrite, DuplicateTransient)
int32 MyInt_DuplicateTransient = 123;
//PropertyFlags: CPF_Edit | CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_NonPIEDuplicateTransient | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
UPROPERTY(EditAnywhere, BlueprintReadWrite, NonPIEDuplicateTransient)
int32 MyInt_NonPIEDuplicateTransient = 123;
};
void UMyProperty_Serialization_Test::RunTest()
{
UMyProperty_Serialization* obj = NewObject<UMyProperty_Serialization>(GetTransientPackage());
obj->MyInt_Default = 456;
obj->MyInt_Transient = 456;
obj->MyInt_DuplicateTransient = 456;
obj->MyInt_NonPIEDuplicateTransient = 456;
//save obj
TArray<uint8> outBytes;
FMemoryWriter MemoryWriter(outBytes, true);
FObjectAndNameAsStringProxyArchive Ar(MemoryWriter, false);
obj->Serialize(Ar);
//load
FMemoryReader MemoryReader(outBytes, true);
FObjectAndNameAsStringProxyArchive Ar2(MemoryReader, true);
UMyProperty_Serialization* obj2 = NewObject<UMyProperty_Serialization>(GetTransientPackage());
obj2->Serialize(Ar2);
}
对这么一个BP DataAsset进行AssetActions→Export，
T3D格式：
Begin Object Class=/Script/Insider.MyProperty_Serialization Name="BP_Serialization" ExportPath="/Script/Insider.MyProperty_Serialization'/Game/Property/BP_Serialization.BP_Serialization'"
MyInt_Default=456
MyInt_DuplicateTransient=456
End Object
COPY格式：
Begin Object Class=/Script/Insider.MyProperty_Serialization Name="BP_Serialization" ExportPath="/Script/Insider.MyProperty_Serialization'/Game/Property/BP_Serialization.BP_Serialization'"
MyInt_Default=456
End Object
如果是普通的序列化：
可见obj2的MyInt_Transient 属性并没有从序列化中获得新值456.
原理代码：
判断CPF_Transient的生效，只有在IsPersistent()的时候，并且不是在保存CDO。SetIsPersistent()的调用在很多地方都出现，比如在MemoryReader/MemoryWriter都是IsPersistent。
因此Transient是在序列化的时候会被忽略。
在ExportText的时候发现会进行CPF_Transient的判断，除非强制进行包括PPF_IncludeTransient
bool FProperty::ShouldSerializeValue(FArchive& Ar) const
{
// Skip the property if the archive says we should
if (Ar.ShouldSkipProperty(this))
{
return false;
}
// Skip non-SaveGame properties if we're saving game state
if (!(PropertyFlags & CPF_SaveGame) && Ar.IsSaveGame())
{
return false;
}
const uint64 SkipFlags = CPF_Transient | CPF_DuplicateTransient | CPF_NonPIEDuplicateTransient | CPF_NonTransactional | CPF_Deprecated | CPF_DevelopmentAssets | CPF_SkipSerialization;
if (!(PropertyFlags & SkipFlags))
{
return true;
}
// Skip properties marked Transient when persisting an object, unless we're saving an archetype
if ((PropertyFlags & CPF_Transient) && Ar.IsPersistent() && !Ar.IsSerializingDefaults())
{
return false;
}
// Skip properties marked DuplicateTransient when duplicating
if ((PropertyFlags & CPF_DuplicateTransient) && (Ar.GetPortFlags() & PPF_Duplicate))
{
return false;
}
// Skip properties marked NonPIEDuplicateTransient when duplicating, but not when we're duplicating for PIE
if ((PropertyFlags & CPF_NonPIEDuplicateTransient) && !(Ar.GetPortFlags() & PPF_DuplicateForPIE) && (Ar.GetPortFlags() & PPF_Duplicate))
{
return false;
}
// Skip properties marked NonTransactional when transacting
if ((PropertyFlags & CPF_NonTransactional) && Ar.IsTransacting())
{
return false;
}
// Skip deprecated properties when saving or transacting, unless the archive has explicitly requested them
if ((PropertyFlags & CPF_Deprecated) && !Ar.HasAllPortFlags(PPF_UseDeprecatedProperties) && (Ar.IsSaving() || Ar.IsTransacting() || Ar.WantBinaryPropertySerialization()))
{
return false;
}
// Skip properties marked SkipSerialization, unless the archive is forcing them
if ((PropertyFlags & CPF_SkipSerialization) && (Ar.WantBinaryPropertySerialization() || !Ar.HasAllPortFlags(PPF_ForceTaggedSerialization)))
{
return false;
}
// Skip editor-only properties when the archive is rejecting them
if (IsEditorOnlyProperty() && Ar.IsFilterEditorOnly())
{
return false;
}
// Otherwise serialize!
return true;
}
///////////////////////////////////////////
bool FProperty::ShouldPort( uint32 PortFlags/*=0*/ ) const
{
// if no size, don't export
if (GetSize() <= 0)
{
return false;
}
if (HasAnyPropertyFlags(CPF_Deprecated) && !(PortFlags & (PPF_ParsingDefaultProperties | PPF_UseDeprecatedProperties)))
{
return false;
}
// if we're parsing default properties or the user indicated that transient properties should be included
if (HasAnyPropertyFlags(CPF_Transient) && !(PortFlags & (PPF_ParsingDefaultProperties | PPF_IncludeTransient)))
{
return false;
}
// if we're copying, treat DuplicateTransient as transient
if ((PortFlags & PPF_Copy) && HasAnyPropertyFlags(CPF_DuplicateTransient | CPF_TextExportTransient) && !(PortFlags & (PPF_ParsingDefaultProperties | PPF_IncludeTransient)))
{
return false;
}
// if we're not copying for PIE and NonPIETransient is set, don't export
if (!(PortFlags & PPF_DuplicateForPIE) && HasAnyPropertyFlags(CPF_NonPIEDuplicateTransient))
{
return false;
}
// if we're only supposed to export components and this isn't a component property, don't export
if ((PortFlags & PPF_SubobjectsOnly) && !ContainsInstancedObjectProperty())
{
return false;
}
// hide non-Edit properties when we're exporting for the property window
if ((PortFlags & PPF_PropertyWindow) && !(PropertyFlags & CPF_Edit))
{
return false;
}
return true;
}
因为不序列Transient属性，因此该属性修改值也并不会被保存起来。打开Asset的时候依然会是默认值，也并不会被复制。
