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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Component/AllowAnyActor.md

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+# AllowAnyActor
+
+- **功能描述：** 用在ComponentReference属性上，在UseComponentPicker的情况下使得组件选取器扩大到场景里其他Actor下的其他组件。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Component Property
+- **元数据类型：** bool
+- **限制类型：** FComponentReference，FSoftComponentReference
+- **关联项：** [UseComponentPicker](UseComponentPicker/UseComponentPicker.md)
+- **常用程度：** ★★
+
+用在ComponentReference属性上，在UseComponentPicker的情况下使得组件选取器扩大到场景里其他Actor下的其他组件。
+
+- 也要注意到，这个AllowAnyActor影响的只是UI上的组件选择。一个ComponentReference即使不加AllowAnyActor，也可以通过ReferencedActor引用到别的Actor，然后手填其属下的组件名字。然后可以正常的在C++里GetComponent里出来正确的组件对象。因此AllowAnyActor跟逻辑无关。
+
+测试代码和效果见UseComponentPicker。
+
+## 原理：
+
+主要是FComponentReferenceCustomization。根据源码查看，bAllowAnyActor 只在已经有bUseComponentPicker的情况下生效，且用来对Actor列表进行过滤。
+
+```cpp
+void FComponentReferenceCustomization::CustomizeHeader(TSharedRef<IPropertyHandle> InPropertyHandle, FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& CustomizationUtils)
+{
+	PropertyHandle = InPropertyHandle;
+
+	CachedComponent.Reset();
+	CachedFirstOuterActor.Reset();
+	CachedPropertyAccess = FPropertyAccess::Fail;
+
+	bAllowClear = false;
+	bAllowAnyActor = false;
+	bUseComponentPicker = PropertyHandle->HasMetaData(NAME_UseComponentPicker);
+	bIsSoftReference = false;
+
+	if (bUseComponentPicker)
+	{
+		FProperty* Property = InPropertyHandle->GetProperty();
+		check(CastField<FStructProperty>(Property) &&
+				(FComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct ||
+				FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct));
+
+		bAllowClear = !(InPropertyHandle->GetMetaDataProperty()->PropertyFlags & CPF_NoClear);
+		bAllowAnyActor = InPropertyHandle->HasMetaData(NAME_AllowAnyActor);
+		bIsSoftReference = FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct;
+
+		BuildClassFilters();
+		BuildComboBox();
+
+		InPropertyHandle->SetOnPropertyValueChanged(FSimpleDelegate::CreateSP(this, &FComponentReferenceCustomization::OnPropertyValueChanged));
+
+		// set cached values
+		{
+			CachedComponent.Reset();
+			CachedFirstOuterActor = GetFirstOuterActor();
+
+			FComponentReference TmpComponentReference;
+			CachedPropertyAccess = GetValue(TmpComponentReference);
+			if (CachedPropertyAccess == FPropertyAccess::Success)
+			{
+				CachedComponent = TmpComponentReference.GetComponent(CachedFirstOuterActor.Get());
+				if (!IsComponentReferenceValid(TmpComponentReference))
+				{
+					CachedComponent.Reset();
+				}
+			}
+		}
+
+		HeaderRow.NameContent()
+		[
+			InPropertyHandle->CreatePropertyNameWidget()
+		]
+		.ValueContent()
+		[
+			ComponentComboButton.ToSharedRef()
+		]
+		.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
+	}
+	else
+	{
+		HeaderRow.NameContent()
+		[
+			InPropertyHandle->CreatePropertyNameWidget()
+		]
+		.ValueContent()
+		[
+			InPropertyHandle->CreatePropertyValueWidget()
+		]
+		.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
+	}
+}
+
+bool FComponentReferenceCustomization::IsFilteredActor(const AActor* const Actor) const
+{
+	return bAllowAnyActor || Actor == CachedFirstOuterActor.Get();
+}
+
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Component/BlueprintSpawnableComponent/BlueprintSpawnableComponent.md

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+# BlueprintSpawnableComponent
+
+- **功能描述：** 允许该组件出现在Actor蓝图里Add组件的面板里。
+- **使用位置：** UCLASS
+- **引擎模块：** Component Property
+- **元数据类型：** bool
+- **限制类型：** Component类
+- **常用程度：** ★★★★
+
+允许该组件出现在Actor蓝图里Add组件的面板里。
+
+在蓝图节点上，不管有没有BlueprintSpawnableComponent则都是可以添加该组件的。
+
+## 测试代码：
+
+```cpp
+UCLASS(Blueprintable, meta = (BlueprintSpawnableComponent))
+class INSIDER_API UMyActorComponent_Spawnable : public UActorComponent
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float MyFloat;
+};
+
+UCLASS(Blueprintable)
+class INSIDER_API UMyActorComponent_NotSpawnable : public UActorComponent
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float MyFloat;
+};
+```
+
+## 蓝图中效果：
+
+可以看到，在Actor的左边Add的按钮下，UMyActorComponent_Spawnable 可以被添加进去，但是UMyActorComponent_NotSpawnable 被阻止了。但同时也要注意到如果在蓝图中AddComponent节点则是都可以的。
+
+![Untitled](Untitled.png)
+
+![Untitled](Untitled%201.png)
+
+## 原理：
+
+```cpp
+bool FKismetEditorUtilities::IsClassABlueprintSpawnableComponent(const UClass* Class)
+{
+	// @fixme: Cooked packages don't have any metadata (yet; they might become available via the sidecar editor data)
+	// However, all uncooked BPs that derive from ActorComponent have the BlueprintSpawnableComponent metadata set on them
+	// (see FBlueprintEditorUtils::RecreateClassMetaData), so include any ActorComponent BP that comes from a cooked package
+	return (!Class->HasAnyClassFlags(CLASS_Abstract) &&
+			Class->IsChildOf<UActorComponent>() &&
+			(Class->HasMetaData(FBlueprintMetadata::MD_BlueprintSpawnableComponent) || Class->GetPackage()->bIsCookedForEditor));
+}
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Component/UseComponentPicker/UseComponentPicker.md

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+# UseComponentPicker
+
+- **功能描述：** 用在ComponentReference属性上，使得选取器的列表里展示出Actor属下的Component以便选择。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Component Property
+- **元数据类型：** bool
+- **限制类型：** FComponentReference，FSoftComponentReference
+- **关联项：** [AllowAnyActor](../AllowAnyActor.md)
+- **常用程度：** ★★
+
+用在ComponentReference属性上，使得选取器的列表里展示出Actor属下的Component以便选择。
+
+- 默认情况下，FComponentReference的Referenced Actor属性展开的选择器列表是让你选择场景里的Actor，因此并不会把该Actor下的组件也都显示出来。而ComponentReference下的ComponentName属性需要玩家手动填写。这种方式比较原始，也容易出错。
+- 因此加上UseComponentPicker后，就可以显示出组件列表来选择。但是又默认限制是当前Actor属下的所有组件，不包括场景里其他Actor里的组件。
+- 如果想要进一步把场景里所有Actor下的所有组件都列出来，则需要进一步加上AllowAnyActor，以扩大筛选范围。
+- ComponentReference的属性类型有两种，FComponentReference和FSoftComponentReference，二者都对应了FComponentReferenceCustomization。测试代码为简洁就没有列出FSoftComponentReference。
+
+## 测试代码：
+
+```cpp
+	UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPickerTest")
+	FComponentReference MyComponentReference_NoUseComponentPicker;
+
+	UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPickerTest", meta = (UseComponentPicker))
+	FComponentReference MyComponentReference_UseComponentPicker;
+
+	UPROPERTY(EditInstanceOnly, BlueprintReadWrite, Category = "UseComponentPicker_AllowAnyActor_Test", meta = (UseComponentPicker,AllowAnyActor))
+	FComponentReference MyComponentReference_UseComponentPicker_AllowAnyActor;
+```
+
+## 测试效果：
+
+- 可见默认的第一个列出了所有Actor，但是ComponentName需要手写。
+- 第二个加上UseComponentPicker后，列出了当前Actor下的所有组件，但是不能选择到其他Actor的组件。
+- 第三个继续加上AllowAnyActor后，列出了所有Actor的所有组件。
+
+![UseComponentPicker](UseComponentPicker.jpg)
+
+## 原理:
+
+FComponentReference和FSoftComponentReference，二者都对应了FComponentReferenceCustomization。看源码可发现用上bUseComponentPicker后，会专门创建ClassFilters和ComboBox，就是采用不同的类型过滤器和不同的UI来选择组件。否则else分支就是很朴素的结构属性展开编辑。
+
+```cpp
+void FComponentReferenceCustomization::CustomizeHeader(TSharedRef<IPropertyHandle> InPropertyHandle, FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& CustomizationUtils)
+{
+	PropertyHandle = InPropertyHandle;
+
+	CachedComponent.Reset();
+	CachedFirstOuterActor.Reset();
+	CachedPropertyAccess = FPropertyAccess::Fail;
+
+	bAllowClear = false;
+	bAllowAnyActor = false;
+	bUseComponentPicker = PropertyHandle->HasMetaData(NAME_UseComponentPicker);
+	bIsSoftReference = false;
+
+	if (bUseComponentPicker)
+	{
+		FProperty* Property = InPropertyHandle->GetProperty();
+		check(CastField<FStructProperty>(Property) &&
+				(FComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct ||
+				FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct));
+
+		bAllowClear = !(InPropertyHandle->GetMetaDataProperty()->PropertyFlags & CPF_NoClear);
+		bAllowAnyActor = InPropertyHandle->HasMetaData(NAME_AllowAnyActor);
+		bIsSoftReference = FSoftComponentReference::StaticStruct() == CastFieldChecked<const FStructProperty>(Property)->Struct;
+
+		BuildClassFilters();
+		BuildComboBox();
+
+		InPropertyHandle->SetOnPropertyValueChanged(FSimpleDelegate::CreateSP(this, &FComponentReferenceCustomization::OnPropertyValueChanged));
+
+		// set cached values
+		{
+			CachedComponent.Reset();
+			CachedFirstOuterActor = GetFirstOuterActor();
+
+			FComponentReference TmpComponentReference;
+			CachedPropertyAccess = GetValue(TmpComponentReference);
+			if (CachedPropertyAccess == FPropertyAccess::Success)
+			{
+				CachedComponent = TmpComponentReference.GetComponent(CachedFirstOuterActor.Get());
+				if (!IsComponentReferenceValid(TmpComponentReference))
+				{
+					CachedComponent.Reset();
+				}
+			}
+		}
+
+		HeaderRow.NameContent()
+		[
+			InPropertyHandle->CreatePropertyNameWidget()
+		]
+		.ValueContent()
+		[
+			ComponentComboButton.ToSharedRef()
+		]
+		.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
+	}
+	else
+	{
+		HeaderRow.NameContent()
+		[
+			InPropertyHandle->CreatePropertyNameWidget()
+		]
+		.ValueContent()
+		[
+			InPropertyHandle->CreatePropertyValueWidget()
+		]
+		.IsEnabled(MakeAttributeSP(this, &FComponentReferenceCustomization::CanEdit));
+	}
+}
+```