UE网络-WithIdentical详解

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WithIdentical是什么

在属性同步时候, 如果想自定义比较函数应该怎么处理呢? WithIdentical就是表明该结构体使用自定义比较函数.

自定义结构体指定WithIdentical

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USTRUCT()
struct FExampleStruct
{
    GENERATED_USTRUCT_BODY()
public:
    UPROPERTY()
    int32		ExampleIntProperty;

    /**
     * @param Ar			FArchive to read or write from.
     * @param Map			PackageMap used to resolve references to UObject*
     * @param bOutSuccess	return value to signify if the serialization was succesfull (if false, an error will be logged by the calling function)
     *
     * @return return true if the serialization was fully mapped. If false, the property will be considered 'dirty' and will replicate again on the next update.
     *	This is needed for UActor* properties. If an actor's Actorchannel is not fully mapped, properties referencing it must stay dirty.
     *	Note that UPackageMap::SerializeObject returns false if an object is unmapped. Generally, you will want to return false from your ::NetSerialize
     *  if you make any calls to ::SerializeObject that return false.
     *
    */
    bool NetSerialize(FArchive& Ar, class UPackageMap* Map, bool& bOutSuccess);

    bool Identical(const FExampleStruct* Other, uint32 PortFlags) const
    {
        return ExampleIntProperty == Other->ExampleIntProperty;
    }
};

template<>
struct TStructOpsTypeTraits< FExampleStruct > : public TStructOpsTypeTraitsBase2< FExampleStruct >
{
    enum
    {
        WithNetSerializer = true,
        WithIdentical = true,
        WithNetSharedSerialization = true,
    };
};

将WithIdentical映射到EStructFlags::STRUCT_IdenticalNative

构建UScriptStruct

在PreInit时候,构建UScriptStruct

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将WithNetSharedSerialization属性映射到EStructFlags::STRUCT_IdenticalNative

构建UScriptStruct, 通过模板, 指定WithIdentical属性.

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好了, 到此为止, 已经将我们指定的WithNetSharedSerialization映射到EStructFlags::STRUCT_IdenticalNative上了. 即UScriptStruct.StructFlags已经包含EStructFlags::STRUCT_IdenticalNative属性.

在比较中使用自定义比较函数

堆栈:

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--UActorChannel.ReplicateActor.if.{ 
 |--FObjectReplicator.ReplicateProperties 
 | |--FNetSerializeCB.UpdateChangelistMgr 
 | | |--FRepLayout.UpdateChangelistMgr 
 | | | |--FRepLayout.CompareProperties.else 
 | | | | |--CompareParentProperties.if.else 
 | | | | | |--UE4_RepLayout_Private.CompareParentPropertyHelper 
 | | | | | | |--CompareParentProperty 
 | | | | | | | |--CompareProperties_r.for 
 | | | | | | | | |--FStructProperty.Identical

在进行属性比较的时候调用PropertiesAreIdentical:

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调用Struct的比较函数:UScriptStruct::CompareScriptStruct, 因为有标志位:STRUCT_IdenticalNative, 所以进行自定义比较.

通过使用Cmd.Property->Identical(A, B)

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最终调用了自定义Identical函数.

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