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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Struct/HasNativeBreak/HasNativeBreak.md

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+# HasNativeBreak
+
+- **功能描述：** 为该结构指定一个C++内的UFunction函数作为Break节点的实现
+- **使用位置：** USTRUCT
+- **引擎模块：** Struct
+- **元数据类型：** string="abc"
+- **关联项：** [HasNativeMake](../HasNativeMake.md)
+- **常用程度：** ★★★★★
+
+为该结构指定一个C++内的UFunction函数作为Break节点的实现
+
+指定一个static *UFunction函数的完整路径值，一般是”/*Script/*Module.Class.Function”*
+
+这个函数一般是BlueprintThreadSafe，因为这种纯Make和Break函数一般不带副作用，因此可以随便的多线程调用。
+
+## 测试代码：
+
+```cpp
+//(BlueprintType = true, HasNativeBreak = /Script/Insider.MyHasNativeStructHelperLibrary.BreakMyHasNativeStruct, HasNativeMake = /Script/Insider.MyHasNativeStructHelperLibrary.MakeMyHasNativeStruct, ModuleRelativePath = Struct/MyStruct_NativeMakeBreak.h)
+USTRUCT(BlueprintType, meta = (HasNativeBreak = "/Script/Insider.MyHasNativeStructHelperLibrary.BreakMyHasNativeStruct", HasNativeMake = "/Script/Insider.MyHasNativeStructHelperLibrary.MakeMyHasNativeStruct"))
+struct INSIDER_API FMyStruct_HasNative
+{
+	GENERATED_BODY()
+
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float MyReadWrite;
+	UPROPERTY(BlueprintReadOnly, EditAnywhere)
+	float MyReadOnly;
+	UPROPERTY(EditAnywhere)
+	float MyNotBlueprint;
+};
+
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyStruct_HasDefaultMakeBreak
+{
+	GENERATED_BODY()
+
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float MyReadWrite;
+	UPROPERTY(BlueprintReadOnly, EditAnywhere)
+	float MyReadOnly;
+	UPROPERTY(EditAnywhere)
+	float MyNotBlueprint;
+};
+
+UCLASS()
+class UMyHasNativeStructHelperLibrary : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+public:
+	UFUNCTION(BlueprintPure, meta = (BlueprintThreadSafe))
+	static void BreakMyHasNativeStruct(const FMyStruct_HasNative& myStruct, float& outValue)
+	{
+		outValue = myStruct.MyReadWrite + myStruct.MyReadOnly + myStruct.MyNotBlueprint;
+	}
+
+	UFUNCTION(BlueprintPure, meta = (BlueprintThreadSafe))
+	static FMyStruct_HasNative MakeMyHasNativeStruct(float value)
+	{
+		FMyStruct_HasNative result;
+		result.MyReadWrite = value;
+		result.MyReadOnly = value;
+		result.MyNotBlueprint = value;
+		return result;
+	}
+};
+```
+
+## 蓝图节点：
+
+![Untitled](Untitled.png)
+
+## 原理是：
+
+通过Meta里配置的值去找UFunction函数，因此我们配置的时候需要提供的是能找到UFunction的完整路径值。这个函数的签名会自动的被反射提取信息到UK2Node_CallFunction节点上，从而构造出不同样式的Make和Break蓝图节点。
+
+```cpp
+E:\P4V\Engine\Source\Editor\BlueprintGraph\Private\EdGraphSchema_K2.cpp
+
+const FString& MetaData = StructType->GetMetaData(FBlueprintMetadata::MD_NativeMakeFunction);
+const UFunction* Function = FindObject<UFunction>(nullptr, *MetaData, true);
+
+UK2Node_CallFunction* CallFunctionNode;
+
+if (Params.bTransient || Params.CompilerContext)
+{
+	CallFunctionNode = (Params.bTransient ? NewObject<UK2Node_CallFunction>(Graph) : Params.CompilerContext->SpawnIntermediateNode<UK2Node_CallFunction>(GraphNode, Params.SourceGraph));
+	CallFunctionNode->SetFromFunction(Function);
+	CallFunctionNode->AllocateDefaultPins();
+}
+else
+{
+	FGraphNodeCreator<UK2Node_CallFunction> MakeStructCreator(*Graph);
+	CallFunctionNode = MakeStructCreator.CreateNode(false);
+	CallFunctionNode->SetFromFunction(Function);
+	MakeStructCreator.Finalize();
+}
+
+SplitPinNode = CallFunctionNode;
+```