106 lines
4.3 KiB
Markdown
106 lines
4.3 KiB
Markdown
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# SealedEvent
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- **功能描述：** 无法在子类中覆盖此函数。SealedEvent关键词只能用于事件。对于非事件函数，请将它们声明为static或final，以密封它们。
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- **元数据类型：** bool
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- **引擎模块：** Behavior
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- **作用机制：** 在FunctionFlags中添加[FUNC_Final](../../../../Flags/EFunctionFlags/FUNC_Final.md)
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在源码里搜索：发现都是用在网络的函数上
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## UHT中的处理：
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```cpp
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//先识别符号
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[UhtSpecifier(Extends = UhtTableNames.Function, ValueType = UhtSpecifierValueType.Legacy)]
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private static void SealedEventSpecifier(UhtSpecifierContext specifierContext)
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{
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UhtFunction function = (UhtFunction)specifierContext.Type;
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function.FunctionExportFlags |= UhtFunctionExportFlags.SealedEvent;
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}
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//再设置标记
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// Handle the initial implicit/explicit final
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// A user can still specify an explicit final after the parameter list as well.
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if (automaticallyFinal || function.FunctionExportFlags.HasAnyFlags(UhtFunctionExportFlags.SealedEvent))
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{
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function.FunctionFlags |= EFunctionFlags.Final;
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function.FunctionExportFlags |= UhtFunctionExportFlags.Final | UhtFunctionExportFlags.AutoFinal;
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}
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再验证：限定只能用在Event上。
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if (FunctionExportFlags.HasAnyFlags(UhtFunctionExportFlags.SealedEvent) && !FunctionFlags.HasAnyFlags(EFunctionFlags.Event))
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{
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this.LogError("SealedEvent may only be used on events");
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}
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if (FunctionExportFlags.HasAnyFlags(UhtFunctionExportFlags.SealedEvent) && FunctionFlags.HasAnyFlags(EFunctionFlags.BlueprintEvent))
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{
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this.LogError("SealedEvent cannot be used on Blueprint events");
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}
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```
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## 测试代码：
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```cpp
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//Error: "SealedEvent may only be used on events"
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UFUNCTION(SealedEvent)
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void MyFunc_SealedEvent() {}
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//Error: "SealedEvent cannot be used on Blueprint events"
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UFUNCTION(BlueprintCallable,BlueprintImplementableEvent,SealedEvent)
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void MyFunc_ImplementableEvent();
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//Error: "SealedEvent cannot be used on Blueprint events"
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UFUNCTION(BlueprintCallable,BlueprintNativeEvent,SealedEvent)
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void MyFunc_NativeEvent();
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```
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因此无法用于普通的函数，又无法用于蓝图中的Event。所以既是Event又不是BlueprintEvent的是什么？看源码是只有网络的一些函数。
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通过对比，发现Sealed函数的区别是多了FUNC_Final的标记。但FUNC_Final又不一定必须要以SealedEvent才能添加，exec或普通的BlueprintCallable函数都会添加。但是如果是vitural的函数就不会添加。在UHT中的原理是：
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```cpp
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private static UhtParseResult ParseUFunction(UhtParsingScope parentScope, UhtToken token)
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{
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if (function.FunctionFlags.HasAnyFlags(EFunctionFlags.Net))
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{
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// Network replicated functions are always events, and are only final if sealed
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scopeName = "event";
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tokenContext.Reset(scopeName);
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automaticallyFinal = false;
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}
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// If virtual, remove the implicit final, the user can still specifying an explicit final at the end of the declaration
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if (function.FunctionExportFlags.HasAnyFlags(UhtFunctionExportFlags.Virtual))
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{
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automaticallyFinal = false;
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}
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// Handle the initial implicit/explicit final
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// A user can still specify an explicit final after the parameter list as well.
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if (automaticallyFinal || function.FunctionExportFlags.HasAnyFlags(UhtFunctionExportFlags.SealedEvent))
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{
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function.FunctionFlags |= EFunctionFlags.Final;
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function.FunctionExportFlags |= UhtFunctionExportFlags.Final | UhtFunctionExportFlags.AutoFinal;
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}
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}
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```
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在自己的C++代码中测试，发现在C++中怎么继承都不会触发编译错误。因此如果想拒绝被继承，还是用C++标准是final关键字。在函数末尾加final。
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E:\P4V\Engine\Source\Editor\KismetCompiler\Private\KismetCompiler.cpp
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```cpp
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const uint32 OverrideFlagsToCheck = (FUNC_FuncOverrideMatch & ~FUNC_AccessSpecifiers);
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if ((Context.Function->FunctionFlags & OverrideFlagsToCheck) != (OverridenFunction->FunctionFlags & OverrideFlagsToCheck))
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{
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MessageLog.Error(*LOCTEXT("IncompatibleOverrideFlags_Error", "Overriden function is not compatible with the parent function @@. Check flags: Exec, Final, Static.").ToString(), Context.EntryPoint);
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}
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```
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在编译的时候检测的是否是重载父类的函数，但因为SealedEvent不作用于普通函数，也不作用于BlueprintEvent，因此感觉只能在C++中继承。
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