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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Blueprint/Latent/NeedsLatentFixup.md

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+# NeedsLatentFixup
+
+- **功能描述：** 用在FLatentActionInfo::Linkage属性上，告诉蓝图VM生成跳转信息
+- **使用位置：** UPROPERTY
+- **元数据类型：** bool
+- **关联项：** [Latent](Latent.md)
+- **常用程度：** ★
+
+## 在源码里找到的用处：
+
+```cpp
+USTRUCT(BlueprintInternalUseOnly)
+struct FLatentActionInfo
+{
+	GENERATED_USTRUCT_BODY()
+
+	/** The resume point within the function to execute */
+	UPROPERTY(meta=(NeedsLatentFixup = true))
+	int32 Linkage;
+
+	//...
+};
+
+```
+
+## 源码里发挥作用的地方：
+
+看着就是把Linkage这个属性进行单独的处理。用来在JumpTargetFixupMap里进行专门的跳转
+
+```cpp
+void EmitLatentInfoTerm(FBPTerminal* Term, FProperty* LatentInfoProperty, FBlueprintCompiledStatement* TargetLabel)
+{
+	// Special case of the struct property emitter.  Needs to emit a linkage property for fixup
+	FStructProperty* StructProperty = CastFieldChecked<FStructProperty>(LatentInfoProperty);
+	check(StructProperty->Struct == LatentInfoStruct);
+
+	int32 StructSize = LatentInfoStruct->GetStructureSize();
+	uint8* StructData = (uint8*)FMemory_Alloca(StructSize);
+	StructProperty->InitializeValue(StructData);
+
+	// Assume that any errors on the import of the name string have been caught in the function call generation
+	StructProperty->ImportText_Direct(*Term->Name, StructData, NULL, 0, GLog);
+
+	Writer << EX_StructConst;
+	Writer << LatentInfoStruct;
+	Writer << StructSize;
+
+	checkSlow(Schema);
+	for (FProperty* Prop = LatentInfoStruct->PropertyLink; Prop; Prop = Prop->PropertyLinkNext)
+	{
+		if (TargetLabel && Prop->GetBoolMetaData(FBlueprintMetadata::MD_NeedsLatentFixup))
+		{
+			// Emit the literal and queue a fixup to correct it once the address is known
+			Writer << EX_SkipOffsetConst;
+			CodeSkipSizeType PatchUpNeededAtOffset = Writer.EmitPlaceholderSkip();
+			JumpTargetFixupMap.Add(PatchUpNeededAtOffset, FCodeSkipInfo(FCodeSkipInfo::Fixup, TargetLabel));
+		}
+		else if (Prop->GetBoolMetaData(FBlueprintMetadata::MD_LatentCallbackTarget))
+		{
+			FBPTerminal CallbackTargetTerm;
+			CallbackTargetTerm.bIsLiteral = true;
+			CallbackTargetTerm.Type.PinSubCategory = UEdGraphSchema_K2::PN_Self;
+			EmitTermExpr(&CallbackTargetTerm, Prop);
+		}
+		else
+		{
+			// Create a new term for each property, and serialize it out
+			FBPTerminal NewTerm;
+			if(Schema->ConvertPropertyToPinType(Prop, NewTerm.Type))
+			{
+				NewTerm.bIsLiteral = true;
+				Prop->ExportText_InContainer(0, NewTerm.Name, StructData, StructData, NULL, PPF_None);
+
+				EmitTermExpr(&NewTerm, Prop);
+			}
+			else
+			{
+				// Do nothing for unsupported/unhandled property types. This will leave the value unchanged from its constructed default.
+				Writer << EX_Nothing;
+			}
+		}
+	}
+
+	Writer << EX_EndStructConst;
+}
+```