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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);
+		}
+	}
+}
+```