68 lines
3.1 KiB
Markdown
68 lines
3.1 KiB
Markdown
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# AllowPrivateAccess
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- **功能描述：** 允许一个在C++中private的属性，可以在蓝图中访问。
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- **使用位置：** UPROPERTY
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- **元数据类型：** bool
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- **关联项：** [BlueprintProtected](../BlueprintProtected/BlueprintProtected.md)
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- **常用程度：** ★★★★★
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允许一个在C++中private的属性，可以在蓝图中访问。
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AllowPrivateAccess的意义是允许这个属性在C++是private的，不允许C++子类访问，但又允许其暴露到蓝图中访问。
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## 测试代码：
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```cpp
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public:
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//CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPublic
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UPROPERTY(BlueprintReadWrite)
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int32 MyNativeInt_NativePublic;
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private:
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//CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPrivate
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//error : BlueprintReadWrite should not be used on private members
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UPROPERTY()
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int32 MyNativeInt_NativePrivate;
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//(AllowPrivateAccess = TRUE, Category = MyFunction_Access, ModuleRelativePath = Function/MyFunction_Access.h)
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//CPF_BlueprintVisible | CPF_ZeroConstructor | CPF_IsPlainOldData | CPF_NoDestructor | CPF_HasGetValueTypeHash | CPF_NativeAccessSpecifierPrivate
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UPROPERTY(BlueprintReadWrite, meta = (AllowPrivateAccess = true))
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int32 MyNativeInt_NativePrivate_AllowPrivateAccess;
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```
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在MyNativeInt_NativePrivate上如果尝试加上BlueprintReadWrite或BlueprintReadOnly都会触发UHT编译报错。
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## 蓝图里的效果：
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默认情况下MyNativeInt_NativePrivate_AllowPrivateAccess在蓝图里的访问权限和MyNativeInt_NativePublic一致。
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如果读者想要修改改属性在蓝图中的访问权限，则可以配合加上BlueprintProtected和BlueprintPrivate。
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## 原理：
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UHT在识别属性的BlueprintReadWrite或BlueprintReadOnly标识符的时候，会同时检测是否有AllowPrivateAccess，没有的话会触发报错。
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因此AllowPrivateAccess的意义其实只是在阻止UHT的报错，这层检测报错过了之后，属性上的BlueprintReadWrite或BlueprintReadOnly就会被识别并发挥作用，从而可以在蓝图中访问。
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```cpp
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private static void BlueprintReadWriteSpecifier(UhtSpecifierContext specifierContext)
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{
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bool allowPrivateAccess = context.MetaData.TryGetValue(UhtNames.AllowPrivateAccess, out string? privateAccessMD) && !privateAccessMD.Equals("false", StringComparison.OrdinalIgnoreCase);
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if (specifierContext.AccessSpecifier == UhtAccessSpecifier.Private && !allowPrivateAccess)
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{
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context.MessageSite.LogError("BlueprintReadWrite should not be used on private members");
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}
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}
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private static void BlueprintReadOnlySpecifier(UhtSpecifierContext specifierContext)
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{
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bool allowPrivateAccess = context.MetaData.TryGetValue(UhtNames.AllowPrivateAccess, out string? privateAccessMD) && !privateAccessMD.Equals("false", StringComparison.OrdinalIgnoreCase);
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if (specifierContext.AccessSpecifier == UhtAccessSpecifier.Private && !allowPrivateAccess)
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{
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context.MessageSite.LogError("BlueprintReadOnly should not be used on private members");
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}
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}
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```
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