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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Enum/ValidEnumValues/ValidEnumValues.md

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+# ValidEnumValues
+
+- **功能描述：** 指定枚举属性值上可选的枚举值选项
+- **使用位置：** UPROPERTY
+- **引擎模块：** Enum Property
+- **元数据类型：** strings="a，b，c"
+- **限制类型：** 枚举属性值
+- **关联项：** [InvalidEnumValues](../InvalidEnumValues.md), [GetRestrictedEnumValues](../GetRestrictedEnumValues.md), [EnumValueDisplayNameOverrides](../EnumValueDisplayNameOverrides/EnumValueDisplayNameOverrides.md), [Enum](../Enum.md)
+- **常用程度：** ★★★
+
+指定枚举属性值上可选的枚举值选项，默认情况下。枚举属性在细节面板上可选项为全部的枚举值，但我们可以通过ValidEnumValues来限制只展示这些值。
+
+枚举属性的写法有3种，分别是enum class，TEnumAsByte和FString叠加enum meta的写法，这3种写法都会被视为一个枚举属性然后尝试产生combo list来让用户选择属性值。
+
+## 示例代码：
+
+```cpp
+UENUM(BlueprintType)
+enum class EMyPropertyTestEnum : uint8
+{
+	First,
+	Second,
+	Third,
+	Forth,
+	Fifth,
+};
+
+UENUM(BlueprintType)
+namespace EMyPropertyTestEnum2
+{
+	enum Type : int
+	{
+		First,
+		Second,
+		Third,
+		Forth,
+		Fifth,
+	};
+}
+
+UCLASS(BlueprintType)
+class INSIDER_API UMyProperty_Enum :public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite)
+	EMyPropertyTestEnum MyEnum;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (ValidEnumValues = "First,Second,Third"))
+	EMyPropertyTestEnum MyEnumWithValid;	// Type 1
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (ValidEnumValues = "First,Second,Third"))
+	TEnumAsByte<EMyPropertyTestEnum2::Type> MyAnotherEnumWithValid;	//Type 2
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (enum = "EMyPropertyTestEnum"))
+	FString MyStringWithEnum;	//Type 3
+	
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (InvalidEnumValues = "First,Second,Third"))
+	EMyPropertyTestEnum MyEnumWithInvalid = EMyPropertyTestEnum::Forth;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (GetRestrictedEnumValues = "MyGetRestrictedEnumValues"))
+	EMyPropertyTestEnum MyEnumWithRestricted;
+
+public:
+	UFUNCTION(BlueprintInternalUseOnly)
+	TArray<FString> MyGetRestrictedEnumValues() const{	return TArray<FString>{"Second","Third"};}
+};
+```
+
+## 蓝图效果：
+
+可见默认情况下枚举属性会显示全部5个枚举值，但其他3个枚举属性值的可选列表被限制到了3个。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+下述的代码，
+
+```cpp
+bool FPropertyHandleBase::GeneratePossibleValues(TArray< TSharedPtr<FString> >& OutOptionStrings, TArray< FText >& OutToolTips, TArray<bool>& OutRestrictedItems)
+{
+	TArray<UObject*> OuterObjects;
+	GetOuterObjects(OuterObjects);		
+	
+	const TArray<FName> ValidEnumValues = PropertyEditorHelpers::GetValidEnumsFromPropertyOverride(Property, Enum);
+	const TArray<FName> InvalidEnumValues = PropertyEditorHelpers::GetInvalidEnumsFromPropertyOverride(Property, Enum);
+	const TArray<FName> RestrictedEnumValues = PropertyEditorHelpers::GetRestrictedEnumsFromPropertyOverride(OuterObjects, Property, Enum);
+	
+	const TMap<FName, FText> EnumValueDisplayNameOverrides = PropertyEditorHelpers::GetEnumValueDisplayNamesFromPropertyOverride(Property, Enum);
+	
+	//NumEnums() - 1, because the last item in an enum is the _MAX item
+	for( int32 EnumIndex = 0; EnumIndex < Enum->NumEnums() - 1; ++EnumIndex )
+	{
+		// Ignore hidden enums
+		bool bShouldBeHidden = Enum->HasMetaData(TEXT("Hidden"), EnumIndex ) || Enum->HasMetaData(TEXT("Spacer"), EnumIndex );
+		if (!bShouldBeHidden)
+		{
+			if(ValidEnumValues.Num() > 0)
+			{
+				bShouldBeHidden = !ValidEnumValues.Contains(Enum->GetNameByIndex(EnumIndex));
+			}
+			// If both are specified, InvalidEnumValues takes precedence
+			else if(InvalidEnumValues.Num() > 0)
+			{
+				bShouldBeHidden = InvalidEnumValues.Contains(Enum->GetNameByIndex(EnumIndex));
+			}
+		}
+	
+		if (!bShouldBeHidden)
+		{
+			bShouldBeHidden = IsHidden(Enum->GetNameStringByIndex(EnumIndex));
+		}
+	
+		if( !bShouldBeHidden )
+		{
+			// See if we specified an alternate name for this value using metadata
+			FString EnumName = Enum->GetNameStringByIndex(EnumIndex);
+			FString EnumDisplayName = EnumValueDisplayNameOverrides.FindRef(Enum->GetNameByIndex(EnumIndex)).ToString();
+			if (EnumDisplayName.IsEmpty())
+			{
+				EnumDisplayName = Enum->GetDisplayNameTextByIndex(EnumIndex).ToString();
+			}
+	
+			FText RestrictionTooltip;
+			const bool bIsRestricted = GenerateRestrictionToolTip(EnumName, RestrictionTooltip) || RestrictedEnumValues.Contains(Enum->GetNameByIndex(EnumIndex));
+			OutRestrictedItems.Add(bIsRestricted);
+	
+			if (EnumDisplayName.Len() == 0)
+			{
+				EnumDisplayName = MoveTemp(EnumName);
+			}
+			else
+			{
+				bUsesAlternateDisplayValues = true;
+			}
+	
+			TSharedPtr< FString > EnumStr(new FString(EnumDisplayName));
+			OutOptionStrings.Add(EnumStr);
+	
+			FText EnumValueToolTip = bIsRestricted ? RestrictionTooltip : Enum->GetToolTipTextByIndex(EnumIndex);
+			OutToolTips.Add(MoveTemp(EnumValueToolTip));
+		}
+		else
+		{
+			OutToolTips.Add(FText());
+		}
+	}
+}
+```