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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Specifier/UPROPERTY/Blueprint/BlueprintReadOnly/BlueprintReadOnly.md

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+# BlueprintReadOnly
+
+- **功能描述：** 此属性可由蓝图读取，但不能被修改。
+- **元数据类型：** bool
+- **引擎模块：** Blueprint
+- **作用机制：** 在PropertyFlags中加入[CPF_BlueprintVisible](../../../../Flags/EPropertyFlags/CPF_BlueprintVisible.md), [CPF_BlueprintReadOnly](../../../../Flags/EPropertyFlags/CPF_BlueprintReadOnly.md)
+- **常用程度：** ★★★★★
+
+此属性可由蓝图读取，但不能被修改。此说明符与 BlueprintReadWrite 说明符不兼容。
+
+## 示例代码：
+
+```cpp
+public:
+	//PropertyFlags:	CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic 
+	UPROPERTY(BlueprintReadWrite, Category = Blueprint)
+		int32 MyInt_ReadWrite = 123;
+	//PropertyFlags:	CPF_BlueprintVisible | CPF_BlueprintReadOnly | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic 
+	UPROPERTY(BlueprintReadOnly, Category = Blueprint)
+		int32 MyInt_ReadOnly = 123;
+```
+
+## 示例效果：
+
+指定蓝图中只读：
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+有CPF_BlueprintVisible 就可以Get
+
+加上CPF_BlueprintReadOnly 后就不能修改。
+
+```cpp
+EPropertyAccessResultFlags PropertyAccessUtil::CanGetPropertyValue(const FProperty* InProp)
+{
+	if (!InProp->HasAnyPropertyFlags(CPF_Edit | CPF_BlueprintVisible | CPF_BlueprintAssignable))
+	{
+		return EPropertyAccessResultFlags::PermissionDenied | EPropertyAccessResultFlags::AccessProtected;
+	}
+
+	return EPropertyAccessResultFlags::Success;
+}
+
+FBlueprintEditorUtils::EPropertyWritableState FBlueprintEditorUtils::IsPropertyWritableInBlueprint(const UBlueprint* Blueprint, const FProperty* Property)
+{
+	if (Property)
+	{
+		if (!Property->HasAnyPropertyFlags(CPF_BlueprintVisible))
+		{
+			return EPropertyWritableState::NotBlueprintVisible;
+		}
+		if (Property->HasAnyPropertyFlags(CPF_BlueprintReadOnly))
+		{
+			return EPropertyWritableState::BlueprintReadOnly;
+		}
+		if (Property->GetBoolMetaData(FBlueprintMetadata::MD_Private))
+		{
+			const UClass* OwningClass = Property->GetOwnerChecked<UClass>();
+			if (OwningClass->ClassGeneratedBy.Get() != Blueprint)
+			{
+				return EPropertyWritableState::Private;
+			}
+		}
+	}
+	return EPropertyWritableState::Writable;
+}
+```