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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/GAS/HideFromModifiers/HideFromModifiers.md

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+# HideFromModifiers
+
+- **功能描述：** 指定AttributeSet下的某属性不出现在GameplayEffect下的Modifiers的Attribute选择里。
+- **使用位置：** UPROPERTY
+- **引擎模块：** GAS
+- **元数据类型：** bool
+- **限制类型：** UAttributeSet下的属性
+- **关联项：** [HideInDetailsView](../HideInDetailsView/HideInDetailsView.md)
+- **常用程度：** ★★★
+
+指定AttributeSet下的某属性不出现在GameplayEffect下的Modifiers的Attribute选择里。
+
+## 测试代码：
+
+```cpp
+UCLASS()
+class UMyAttributeSet : public UAttributeSet
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core")
+	float HP = 100.f;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core", meta = (HideInDetailsView))
+	float HP_HideInDetailsView = 100.f;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core", meta = (HideFromModifiers))
+	float HP_HideFromModifiers = 100.f;
+};
+UCLASS()
+class UMyAttributeSetTest : public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "GAS")
+	FGameplayAttribute MyAttribute;
+};
+```
+
+## 测试结果：
+
+在蓝图中创建一个GameplayEffect，然后观察其Modifiers下的Attribute选择。
+
+发现HP_HideFromModifiers 可以出现在正常的FGameplayAttribute 选项卡中，但不能出现在Modifiers下的Attribute选项卡里。这就是这里的作用。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+在FGameplayModifierInfo的Attribute属性上有FilterMetaTag的元数据，然后取出其里面的值，最终还是传到GetAllAttributeProperties作为FilterMetaStr来过滤。因此属性上出现HideFromModifiers就不能出现。
+
+```cpp
+USTRUCT(BlueprintType)
+struct GAMEPLAYABILITIES_API FGameplayModifierInfo
+{
+	GENERATED_USTRUCT_BODY()
+	
+	/** The Attribute we modify or the GE we modify modifies. */
+	UPROPERTY(EditDefaultsOnly, Category=GameplayModifier, meta=(FilterMetaTag="HideFromModifiers"))
+	FGameplayAttribute Attribute;
+};
+
+void FAttributePropertyDetails::CustomizeHeader( TSharedRef<IPropertyHandle> StructPropertyHandle, class FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& StructCustomizationUtils )
+{
+		const FString& FilterMetaStr = StructPropertyHandle->GetProperty()->GetMetaData(TEXT("FilterMetaTag"));
+	SNew(SGameplayAttributeWidget)
+	.OnAttributeChanged(this, &FAttributePropertyDetails::OnAttributeChanged)
+	.DefaultProperty(PropertyValue)
+	.FilterMetaData(FilterMetaStr)
+}
+void FGameplayAttribute::GetAllAttributeProperties(TArray<FProperty*>& OutProperties, FString FilterMetaStr, bool UseEditorOnlyData)
+{}
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/GAS/HideInDetailsView/HideInDetailsView.md

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+# HideInDetailsView
+
+- **功能描述：** 把该UAttributeSet子类里的属性隐藏在FGameplayAttribute的选项列表里。
+- **使用位置：** UCLASS, UPROPERTY
+- **引擎模块：** GAS
+- **元数据类型：** bool
+- **限制类型：** UAttributeSet
+- **关联项：** [HideFromModifiers](../HideFromModifiers/HideFromModifiers.md), [SystemGameplayAttribute](../SystemGameplayAttribute/SystemGameplayAttribute.md)
+- **常用程度：** ★★★
+
+把该UAttributeSet子类里的属性隐藏在FGameplayAttribute的选项列表里。
+
+可用在UCLASS上隐藏掉整个类里的所有属性，也可以用在某个特定属性上只隐藏该属性。
+
+在源码里用到的例子是UAbilitySystemTestAttributeSet，因为其就是一个专门用来测试的AS，因此希望不影响正常的选项列表。
+
+## 测试代码：
+
+```cpp
+UCLASS()
+class UMyAttributeSet : public UAttributeSet
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core")
+	float HP = 100.f;
+	
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core", meta = (HideInDetailsView))
+	float HP_HideInDetailsView = 100.f;
+};
+
+UCLASS(meta = (HideInDetailsView))
+class UMyAttributeSet_Hide : public UAttributeSet
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Core")
+	float HP = 100.f;
+};
+
+UCLASS()
+class UMyAttributeSetTest : public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "GAS")
+	FGameplayAttribute MyAttribute;
+};
+```
+
+## 测试效果：
+
+可见只能选到UMyAttributeSet.HP属性，无法选择到UMyAttributeSet_Hide里的选项。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+```cpp
+PropertyModule.RegisterCustomPropertyTypeLayout( "GameplayAttribute", FOnGetPropertyTypeCustomizationInstance::CreateStatic( &FAttributePropertyDetails::MakeInstance ) );
+
+void FGameplayAttribute::GetAllAttributeProperties(TArray<FProperty*>& OutProperties, FString FilterMetaStr, bool UseEditorOnlyData)
+{
+	for (TObjectIterator<UClass> ClassIt; ClassIt; ++ClassIt)
+	{
+		if (UseEditorOnlyData)
+		{
+			#if WITH_EDITOR
+			// Allow entire classes to be filtered globally
+			if (Class->HasMetaData(TEXT("HideInDetailsView")))
+			{
+				continue;
+			}
+			#endif
+		}
+		
+		
+			for (TFieldIterator<FProperty> PropertyIt(Class, EFieldIteratorFlags::ExcludeSuper); PropertyIt; ++PropertyIt)
+			{
+				FProperty* Property = *PropertyIt;
+
+				if (UseEditorOnlyData)
+				{
+					// Allow properties to be filtered globally (never show up)
+					if (Property->HasMetaData(TEXT("HideInDetailsView")))
+					{
+						continue;
+					}
+					#endif
+				}
+				
+				OutProperties.Add(Property);
+			}
+	}
+}
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/GAS/SystemGameplayAttribute/SystemGameplayAttribute.md

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+# SystemGameplayAttribute
+
+- **功能描述：** 把UAbilitySystemComponent子类里面的属性暴露到FGameplayAttribute 选项框里。
+- **使用位置：** UPROPERTY
+- **引擎模块：** GAS
+- **元数据类型：** bool
+- **限制类型：** UAbilitySystemComponent子类里面的属性
+- **关联项：** [HideInDetailsView](../HideInDetailsView/HideInDetailsView.md)
+- **常用程度：** ★★★
+
+把UAbilitySystemComponent子类里面的属性暴露到FGameplayAttribute 选项框里。
+
+## 源码例子：
+
+```cpp
+UCLASS(ClassGroup=AbilitySystem, hidecategories=(Object,LOD,Lighting,Transform,Sockets,TextureStreaming), editinlinenew, meta=(BlueprintSpawnableComponent))
+class GAMEPLAYABILITIES_API UAbilitySystemComponent : public UGameplayTasksComponent, public IGameplayTagAssetInterface, public IAbilitySystemReplicationProxyInterface
+{
+	/** Internal Attribute that modifies the duration of gameplay effects created by this component */
+	UPROPERTY(meta=(SystemGameplayAttribute="true"))
+	float OutgoingDuration;
+
+	/** Internal Attribute that modifies the duration of gameplay effects applied to this component */
+	UPROPERTY(meta = (SystemGameplayAttribute = "true"))
+	float IncomingDuration;
+}
+```
+
+## 测试代码：
+
+```cpp
+UCLASS(Blueprintable, BlueprintType)
+class UMyAbilitySystemComponent : public UAbilitySystemComponent
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "GAS")
+	float MyFloat;
+
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "GAS", meta = (SystemGameplayAttribute))
+	float MyFloat_System;
+};
+
+UCLASS()
+class UMyAttributeSetTest : public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "GAS")
+	FGameplayAttribute MyAttribute;
+};
+
+```
+
+## 测试效果：
+
+可见MyFloat_System可以暴露到选项列表里去。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+也是在GetAllAttributeProperties判断属性上的SystemGameplayAttribute标记。
+
+```cpp
+void FGameplayAttribute::GetAllAttributeProperties(TArray<FProperty*>& OutProperties, FString FilterMetaStr, bool UseEditorOnlyData)
+{
+	// UAbilitySystemComponent can add 'system' attributes
+	if (Class->IsChildOf(UAbilitySystemComponent::StaticClass()) && !Class->ClassGeneratedBy)
+	{
+		for (TFieldIterator<FProperty> PropertyIt(Class, EFieldIteratorFlags::ExcludeSuper); PropertyIt; ++PropertyIt)
+		{
+			FProperty* Property = *PropertyIt;
+	
+	
+			// SystemAttributes have to be explicitly tagged
+			if (Property->HasMetaData(TEXT("SystemGameplayAttribute")) == false)
+			{
+				continue;
+			}
+			OutProperties.Add(Property);
+		}
+	}
+}
+```