140 lines
5.8 KiB
Markdown
140 lines
5.8 KiB
Markdown
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# ChildCanTick
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- **功能描述：** 标记允许其蓝图子类可以接受响应Tick事件
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- **使用位置：** UCLASS
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- **引擎模块：** Actor
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- **元数据类型：** bool
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- **限制类型：** Actor或ActorComponent子类
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- **关联项：** [ChildCannotTick](../ChildCannotTick.md)
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- **常用程度：** ★★★
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要在蓝图中重载Tick事件函数并只会在编译的时候触发判断。
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```cpp
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//(BlueprintType = true, ChildCannotTick = , IncludePath = Class/Blueprint/MyActor_ChildTick.h, IsBlueprintBase = true, ModuleRelativePath = Class/Blueprint/MyActor_ChildTick.h)
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UCLASS(Blueprintable,meta=(ChildCanTick))
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class INSIDER_API AMyActor_ChildCanTick : public AActor
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{
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GENERATED_BODY()
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public:
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AMyActor_ChildCanTick()
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{
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PrimaryActorTick.bCanEverTick = false;
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}
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};
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//(BlueprintType = true, ChildCanTick = , IncludePath = Class/Blueprint/MyActor_ChildTick.h, IsBlueprintBase = true, ModuleRelativePath = Class/Blueprint/MyActor_ChildTick.h)
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UCLASS(Blueprintable,meta=(ChildCanTick))
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class INSIDER_API UMyActorComponent_ChildCanTick : public UActorComponent
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{
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GENERATED_BODY()
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public:
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};
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//(BlueprintType = true, ChildCannotTick = , IncludePath = Class/Blueprint/MyActor_ChildTick.h, IsBlueprintBase = true, ModuleRelativePath = Class/Blueprint/MyActor_ChildTick.h)
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UCLASS(Blueprintable,meta=(ChildCannotTick))
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class INSIDER_API AMyActor_ChildCannotTick : public AActor
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{
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GENERATED_BODY()
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public:
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};
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//(BlueprintType = true, ChildCannotTick = , IncludePath = Class/Blueprint/MyActor_ChildTick.h, IsBlueprintBase = true, ModuleRelativePath = Class/Blueprint/MyActor_ChildTick.h)
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UCLASS(Blueprintable,meta=(ChildCannotTick))
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class INSIDER_API UMyActorComponent_ChildCannotTick : public UActorComponent
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{
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GENERATED_BODY()
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public:
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};
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```
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蓝图Actor或ActorComponent里测试：
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也注意到这个判断跟蓝图中是否开启Tick并没有关系。
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而AMyActor_ChildCanTick类里虽然已经手动关闭了PrimaryActorTick.bCanEverTick，但是在子类里依然可以正常的Tick（在编译的时候内部可以正常的再重新开启bCanEverTick）。
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## 源码里判断的逻辑：
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开启bCanEverTick=true的条件有3，一是EngineSettings->bCanBlueprintsTickByDefault，二是父类是AActor或UActorComponent本身，三是C++基类上有ChildCanTick的标记。
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```cpp
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void FKismetCompilerContext::SetCanEverTick() const
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{
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// RECEIVE TICK
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if (!TickFunction->bCanEverTick)
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{
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// Make sure that both AActor and UActorComponent have the same name for their tick method
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static FName ReceiveTickName(GET_FUNCTION_NAME_CHECKED(AActor, ReceiveTick));
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static FName ComponentReceiveTickName(GET_FUNCTION_NAME_CHECKED(UActorComponent, ReceiveTick));
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if (const UFunction* ReceiveTickEvent = FKismetCompilerUtilities::FindOverriddenImplementableEvent(ReceiveTickName, NewClass))
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{
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// We have a tick node, but are we allowed to?
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const UEngine* EngineSettings = GetDefault<UEngine>();
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const bool bAllowTickingByDefault = EngineSettings->bCanBlueprintsTickByDefault;
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const UClass* FirstNativeClass = FBlueprintEditorUtils::FindFirstNativeClass(NewClass);
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const bool bHasCanTickMetadata = (FirstNativeClass != nullptr) && FirstNativeClass->HasMetaData(FBlueprintMetadata::MD_ChildCanTick);
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const bool bHasCannotTickMetadata = (FirstNativeClass != nullptr) && FirstNativeClass->HasMetaData(FBlueprintMetadata::MD_ChildCannotTick);
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const bool bHasUniversalParent = (FirstNativeClass != nullptr) && ((AActor::StaticClass() == FirstNativeClass) || (UActorComponent::StaticClass() == FirstNativeClass));
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if (bHasCanTickMetadata && bHasCannotTickMetadata)
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{
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// User error: The C++ class has conflicting metadata
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const FString ConlictingMetadataWarning = FText::Format(
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LOCTEXT("HasBothCanAndCannotMetadataFmt", "Native class %s has both '{0}' and '{1}' metadata specified, they are mutually exclusive and '{1}' will win."),
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FText::FromString(FirstNativeClass->GetPathName()),
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FText::FromName(FBlueprintMetadata::MD_ChildCanTick),
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FText::FromName(FBlueprintMetadata::MD_ChildCannotTick)
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).ToString();
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MessageLog.Warning(*ConlictingMetadataWarning);
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}
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if (bHasCannotTickMetadata)
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{
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// This could only happen if someone adds bad metadata to AActor or UActorComponent directly
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check(!bHasUniversalParent);
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// Parent class has forbidden us to tick
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const FString NativeClassSaidNo = FText::Format(
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LOCTEXT("NativeClassProhibitsTickingFmt", "@@ is not allowed as the C++ parent class {0} has disallowed Blueprint subclasses from ticking. Please consider using a Timer instead of Tick."),
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FText::FromString(FirstNativeClass->GetPathName())
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).ToString();
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MessageLog.Warning(*NativeClassSaidNo, FindLocalEntryPoint(ReceiveTickEvent));
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}
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else
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{
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if (bAllowTickingByDefault || bHasUniversalParent || bHasCanTickMetadata)
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{
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// We're allowed to tick for one reason or another
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TickFunction->bCanEverTick = true;
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}
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else
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{
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// Nothing allowing us to tick
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const FString ReceiveTickEventWarning = FText::Format(
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LOCTEXT("ReceiveTick_CanNeverTickFmt", "@@ is not allowed for Blueprints based on the C++ parent class {0}, so it will never Tick!"),
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FText::FromString(FirstNativeClass ? *FirstNativeClass->GetPathName() : TEXT("<null>"))
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).ToString();
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MessageLog.Warning(*ReceiveTickEventWarning, FindLocalEntryPoint(ReceiveTickEvent));
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const FString ReceiveTickEventRemedies = FText::Format(
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LOCTEXT("ReceiveTick_CanNeverTickRemediesFmt", "You can solve this in several ways:\n 1) Consider using a Timer instead of Tick.\n 2) Add meta=({0}) to the parent C++ class\n 3) Reparent the Blueprint to AActor or UActorComponent, which can always tick."),
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FText::FromName(FBlueprintMetadata::MD_ChildCanTick)
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).ToString();
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MessageLog.Warning(*ReceiveTickEventRemedies);
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}
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}
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}
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}
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}
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```
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