vault backup: 2024-10-12 17:19:45

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/UPARAM/Blueprint/Required/Required.md

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+# Required
+
+- **功能描述：** 指定函数的参数节点必须连接提供一个值
+
+- **元数据类型：** bool
+- **引擎模块：** Blueprint, Parameter
+- **作用机制：** 在PropertyFlags中加入[CPF_RequiredParm](../../../../Flags/EPropertyFlags/CPF_RequiredParm.md)
+- **常用程度：** ★★
+
+指定函数的参数节点必须连接个变量来提供一个值。
+
+如果参数上有提供默认值，该标志依然会忽略默认值，认为还是没提供值。还是必须要连接变量。
+
+## 测试代码：
+
+```cpp
+//PropertyFlags:	CPF_Parm | CPF_ZeroConstructor | CPF_RequiredParm | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic 
+	UFUNCTION(BlueprintCallable)
+	FString MyFuncTestParam_RequiredObject(UPARAM(Required) UObject* objValue);
+
+	//(CPP_Default_intValue = 123, ModuleRelativePath = Function/Param/MyFunction_TestParam.h)
+	//PropertyFlags:	CPF_Parm | CPF_ZeroConstructor | CPF_RequiredParm | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic 
+	UFUNCTION(BlueprintCallable)
+	FString MyFuncTestParam_RequiredInt(UPARAM(Required) int intValue=123);
+```
+
+## 蓝图节点：
+
+![Untitled](Untitled.png)
+
+如果不连一个节点，编译时会报错：
+
+Pin  Int Value  must be linked to another node (in  My Func Test Param Required Int )
+Pin  Obj Value  must be linked to another node (in  My Func Test Param Required Object )
+
+## 原理：
+
+根据这个标记来判断。
+
+```cpp
+const bool bIsRequiredParam = Param->HasAnyPropertyFlags(CPF_RequiredParm);
+	// Don't let the user edit the default value if the parameter is required to be explicit.
+	Pin->bDefaultValueIsIgnored |= bIsRequiredParam;
+```