83 lines
3.0 KiB
Markdown
83 lines
3.0 KiB
Markdown
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# DisableNativeTick
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- **功能描述：** 禁用该UserWidget的NativeTick。
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- **使用位置：** UCLASS
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- **引擎模块：** Widget Property
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- **元数据类型：** bool
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- **限制类型：** UserWidget的子类
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- **常用程度：** ★★★
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禁用该UserWidget的NativeTick。
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如果只有C++类则不起作用，因为纯C++的Widget没有WidgetBPClass 。
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而且BP的子类要删除Tick蓝图节点。
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## 测试代码：
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```cpp
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UCLASS(BlueprintType, meta=())
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class INSIDER_API UMyWidget_WithNativeTick :public UUserWidget
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{
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GENERATED_BODY()
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public:
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virtual void NativeTick(const FGeometry& MyGeometry, float InDeltaTime) override
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{
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Super::NativeTick(MyGeometry, InDeltaTime);
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UKismetSystemLibrary::PrintString(nullptr, TEXT("WithNativeTick"), true);
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}
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};
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UCLASS(BlueprintType,meta=(DisableNativeTick))
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class INSIDER_API UMyWidget_DisableNativeTick :public UUserWidget
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{
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GENERATED_BODY()
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public:
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virtual void NativeTick(const FGeometry& MyGeometry, float InDeltaTime) override
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{
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Super::NativeTick(MyGeometry, InDeltaTime);
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UKismetSystemLibrary::PrintString(nullptr, TEXT("DisableNativeTick"), true);
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}
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};
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```
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## 测试效果：
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在蓝图中分别创建UMyWidget_WithNativeTick 和UMyWidget_DisableNativeTick 的子类UMG_WithTick和UMG_DisableTick。然后把他们都添加到一个UMG里，添加到屏幕上后观察NativeTick的调用情况。
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可见只有WithNativeTick调用。
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## 原理：
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在UCLASS上标记会导致UMG蓝图的bClassRequiresNativeTick=false。继而在UUserWidget的UpdateCanTick里判断。如果WidgetBPClass不为空（是蓝图子类）且ClassRequiresNativeTick为false，bCanTick 才一开始为false。然后判断bHasScriptImplementedTick则要求蓝图中没有EventTick（默认会创建，自己要手动删掉）。然后后面继续判断要没有延迟蓝图节点，没有动画。总之就是这个Widget要真的没有Tick的需求，则可以真的最后bCanTick=false。
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```cpp
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void UWidgetBlueprint::UpdateTickabilityStats(bool& OutHasLatentActions, bool& OutHasAnimations, bool& OutClassRequiresNativeTick)
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{
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static const FName DisableNativeTickMetaTag("DisableNativeTick");
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const bool bClassRequiresNativeTick = !NativeParent->HasMetaData(DisableNativeTickMetaTag);
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OutClassRequiresNativeTick = bClassRequiresNativeTick;
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}
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void FWidgetBlueprintCompilerContext::CopyTermDefaultsToDefaultObject(UObject* DefaultObject)
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{
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WidgetBP->UpdateTickabilityStats(bClassOrParentsHaveLatentActions, bClassOrParentsHaveAnimations, bClassRequiresNativeTick);
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WidgetClass->SetClassRequiresNativeTick(bClassRequiresNativeTick);
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}
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void UUserWidget::UpdateCanTick()
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{
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UWidgetBlueprintGeneratedClass* WidgetBPClass = Cast<UWidgetBlueprintGeneratedClass>(GetClass());
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bCanTick |= !WidgetBPClass || WidgetBPClass->ClassRequiresNativeTick();
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bCanTick |= bHasScriptImplementedTick;
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bCanTick |= World->GetLatentActionManager().GetNumActionsForObject(this) != 0;
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bCanTick |= ActiveSequencePlayers.Num() > 0;
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bCanTick |= QueuedWidgetAnimationTransitions.Num() > 0;
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SafeGCWidget->SetCanTick(bCanTick);
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}
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```
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