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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Asset/DisallowedAssetDataTags.md

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+# DisallowedAssetDataTags
+
+- **功能描述：** 在UObject*属性上指定Tags来进行过滤，必须没有拥有该Tags才可以被选择。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Asset Property
+- **元数据类型：** strings="a=b，c=d，e=f"
+- **限制类型：** UObject*
+- **关联项：** [RequiredAssetDataTags](RequiredAssetDataTags/RequiredAssetDataTags.md), [AssetRegistrySearchable](../../Specifier/UPROPERTY/Asset/AssetRegistrySearchable/AssetRegistrySearchable.md)
+- **常用程度：** ★★

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Asset/ForceShowEngineContent/ForceShowEngineContent.md

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+# ForceShowEngineContent
+
+- **功能描述：** 指定UObject*属性的资源可选列表里强制可选引擎的内建资源
+- **使用位置：** UPROPERTY
+- **引擎模块：** Asset Property
+- **元数据类型：** bool
+- **限制类型：** UObject*
+- **关联项：** [ForceShowPluginContent](ForceShowPluginContent.md)
+- **常用程度：** ★★
+
+指定UObject*属性的资源可选列表里强制可选引擎的内建资源。
+
+## 测试代码：
+
+```cpp
+UCLASS(Blueprintable, BlueprintType)
+class INSIDER_API UMyProperty_ShowContent :public UDataAsset
+{
+public:
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object)
+	TObjectPtr<UObject> MyAsset_Default;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object, meta = (ForceShowEngineContent))
+	TObjectPtr<UObject> MyAsset_ForceShowEngineContent;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object, meta = (ForceShowPluginContent))
+	TObjectPtr<UObject> MyAsset_ForceShowPluginContent;
+};
+```
+
+## 测试结果：
+
+可见MyAsset_Default默认是只包含本项目的资源。
+
+MyAsset_ForceShowEngineContent的作用其实就是在选项卡里勾选ShowEngineContent，因此结果上会发现多了非常多的可选资源。
+
+MyAsset_ForceShowPluginContent的作用同样是在选项卡里勾选ShowPluginContent，可以选择别的插件里的资源。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+在属性的资源选择器里会尝试寻找ForceShowEngineContent和ForceShowPluginContent，然后设置到AssetPickerConfig里，从而改变资源的可选类型。
+
+```cpp
+void SPropertyMenuAssetPicker::Construct( const FArguments& InArgs )
+{
+		const bool bForceShowEngineContent = PropertyHandle ? PropertyHandle->HasMetaData(TEXT("ForceShowEngineContent")) : false;
+		const bool bForceShowPluginContent = PropertyHandle ? PropertyHandle->HasMetaData(TEXT("ForceShowPluginContent")) : false;
+		
+		FAssetPickerConfig AssetPickerConfig;
+		// Force show engine content if meta data says so
+		AssetPickerConfig.bForceShowEngineContent = bForceShowEngineContent;
+		// Force show plugin content if meta data says so
+		AssetPickerConfig.bForceShowPluginContent = bForceShowPluginContent;
+}
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Asset/ForceShowEngineContent/ForceShowPluginContent.md

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+# ForceShowPluginContent
+
+- **功能描述：** 指定UObject*属性的资源可选列表里强制可选其他插件里的内建资源
+- **使用位置：** UPROPERTY
+- **引擎模块：** Asset Property
+- **元数据类型：** bool
+- **限制类型：** UObject*
+- **关联项：** [ForceShowEngineContent](ForceShowEngineContent.md)

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Asset/GetAssetFilter/GetAssetFilter.md

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+# GetAssetFilter
+
+- **功能描述：** 指定一个UFUNCTION来对UObject*属性的可选资源进行排除过滤。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Asset Property
+- **元数据类型：** string="abc"
+- **限制类型：** UObject*
+- **常用程度：** ★★★
+
+指定一个UFUNCTION来对UObject*属性的可选资源进行排除过滤。
+
+- 指定的函数名字必须是UFUNCTION，在本类中定义。
+- 函数的原型是bool FuncName(const FAssetData& AssetData) const;，返回true来排除掉该资产。
+- 这是一种让用户自定义资产过滤的方式。
+
+## 测试代码：
+
+```cpp
+UCLASS(Blueprintable, BlueprintType)
+class INSIDER_API UMyProperty_GetAssetFilter :public UDataAsset
+{
+public:
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite)
+	UObject* MyAsset_Default;
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (GetAssetFilter = "IsShouldFilterAsset"))
+	UObject* MyAsset_GetAssetFilter;
+public:
+	UFUNCTION()
+	bool IsShouldFilterAsset(const FAssetData& AssetData)
+	{
+		return !AssetData.IsInstanceOf<UDataAsset>();
+	}
+};
+```
+
+## 测试效果：
+
+可以见到，MyAsset_GetAssetFilter进行过滤后只允许DataAsset类型的资产。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+在SPropertyEditorAsset（对应UObject类型属性）中有判断GetAssetFilter的meta，得到函数并附加到资产排除的回调里去。
+
+```cpp
+void SPropertyEditorAsset::Construct(const FArguments& InArgs, const TSharedPtr<FPropertyEditor>& InPropertyEditor)
+{
+	if (Property && Property->GetOwnerProperty()->HasMetaData("GetAssetFilter"))
+{
+	// Add MetaData asset filter
+	const FString GetAssetFilterFunctionName = Property->GetOwnerProperty()->GetMetaData("GetAssetFilter");
+	if (!GetAssetFilterFunctionName.IsEmpty())
+	{
+		TArray<UObject*> ObjectList;
+		if (PropertyEditor.IsValid())
+		{
+			PropertyEditor->GetPropertyHandle()->GetOuterObjects(ObjectList);
+		}
+		else if (PropertyHandle.IsValid())
+		{
+			PropertyHandle->GetOuterObjects(ObjectList);
+		}
+		for (UObject* Object : ObjectList)
+		{
+			const UFunction* GetAssetFilterFunction = Object ? Object->FindFunction(*GetAssetFilterFunctionName) : nullptr;
+			if (GetAssetFilterFunction)
+			{
+				AppendOnShouldFilterAssetCallback(FOnShouldFilterAsset::CreateUFunction(Object, GetAssetFilterFunction->GetFName()));
+			}
+		}
+	}
+}
+}
+```

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Asset/RequiredAssetDataTags/RequiredAssetDataTags.md

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+# RequiredAssetDataTags
+
+- **功能描述：** 在UObject*属性上指定Tags来进行过滤，必须拥有该Tags才可以被选择。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Asset Property
+- **元数据类型：** strings="a=b，c=d，e=f"
+- **限制类型：** UObject*
+- **关联项：** [DisallowedAssetDataTags](../DisallowedAssetDataTags.md), [AssetRegistrySearchable](../../../Specifier/UPROPERTY/Asset/AssetRegistrySearchable/AssetRegistrySearchable.md)
+- **常用程度：** ★★
+
+在UObject*属性上指定Tags来进行过滤，必须拥有该Tags才可以被选择。
+
+相关联的可参考AssetRegistrySearchable标识符和GetAssetRegistryTags 方法。
+
+## 测试代码：
+
+```cpp
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyTableRow_Required :public FTableRowBase
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	int32 MyInt = 123;
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FString MyString;
+};
+
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyTableRow_Disallowed :public FTableRowBase
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	float MyFloat = 123.f;
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	UTexture2D* MyTexture;
+};
+
+UCLASS(Blueprintable, BlueprintType)
+class INSIDER_API UMyProperty_AssetDataTags :public UDataAsset
+{
+public:
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object)
+	TObjectPtr<UObject> MyAsset_Default;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object, meta = (RequiredAssetDataTags = "MyIdForSearch=MyId456"))
+	TObjectPtr<UObject> MyAsset_RequiredAssetDataTags;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Object, meta = (DisallowedAssetDataTags = "MyOtherId=MyOtherId789"))
+	TObjectPtr<UObject> MyAsset_DisallowedAssetDataTags;
+public:
+	UPROPERTY(EditAnywhere, Category = DataTable)
+	TObjectPtr<class UDataTable> MyDataTable_Default;
+
+	UPROPERTY(EditAnywhere, Category = DataTable, meta = (RequiredAssetDataTags = "RowStructure=/Script/Insider.MyTableRow_Required"))
+	TObjectPtr<class UDataTable> MyDataTable_RequiredAssetDataTags;
+
+	UPROPERTY(EditAnywhere, Category = DataTable, meta = (DisallowedAssetDataTags = "RowStructure=/Script/Insider.MyTableRow_Disallowed"))
+	TObjectPtr<class UDataTable> MyDataTable_DisallowedAssetDataTags;
+};
+```
+
+## 测试效果：
+
+如上面代码所见，定义了两个不同类型的FTableRowBase，并且也创建了两个DataTable。同时也有两个DataAsset（AssetRegistrySearchable的例子里定义的结构）都有MyIdForSearch和MyOtherId的Tag，但是有不同的值，以此来进行区分。
+
+- MyAsset_Default，可以筛选出所有的对象，图中示例有730个。
+- MyAsset_RequiredAssetDataTags，因为加了RequiredAssetDataTags ，只有DA_MyPropertySearch符合，因为MyIdForSearch=MyId456。
+- MyAsset_DisallowedAssetDataTags，把DA_MyPropertySearch_Disallowed过滤掉了，因为我配置的MyOtherId=MyOtherId789，因此只剩下729个。
+- 关于DataTable也是同理。MyDataTable_Default可以获取所有的DataTable（有3个），而MyDataTable_RequiredAssetDataTags限制了RowStructure只能是FMyTableRow_Required （因此只能筛选出一个）。MyDataTable_DisallowedAssetDataTags排除掉一个RowStructure为FMyTableRow_Disallowed 的，因此就剩下2个。
+
+![Untitled](Untitled.png)
+
+## 源码中例子：
+
+```cpp
+	UPROPERTY(Category="StateTree", EditAnywhere, meta=(RequiredAssetDataTags="Schema=/Script/MassAIBehavior.MassStateTreeSchema"))
+	TObjectPtr<UStateTree> StateTree;
+	
+	UPROPERTY(EditAnywhere, Category=Appearance, meta = (RequiredAssetDataTags = "RowStructure=/Script/UMG.RichImageRow"))
+	TObjectPtr<class UDataTable> ImageSet;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category=Compositing, meta = (AllowPrivateAccess, RequiredAssetDataTags = "IsSourceValid=True"), Setter = SetCompositeTexture, Getter = GetCompositeTexture)
+	TObjectPtr<class UTexture> CompositeTexture;
+```
+
+## 原理:
+
+在UObject*属性上RequiredAssetDataTags和DisallowedAssetDataTags的配置，会在这个属性的编辑器（SPropertyEditorAsset）初始化的时候解析提取到其成员变量RequiredAssetDataTags和DisallowedAssetDataTags里，本质就是个键值对。而后续在进行Asset过滤的时候（IsAssetFiltered的调用），就会开始把FAssetData里的Tags去匹配该属性的Tags需求。Disallowed的出现就排除掉，Required的必须拥有才不会被过滤，最终实现了过滤效果。
+
+关于FAssetData里的Tags，可以参考AssetRegistrySearchable标识符和GetAssetRegistryTags 方法的调用和实现，简单来说就是在对象上会有个方式主动提供Tags给AssetRegistry。
+
+关于DataTable为何可以通过RowStructure过滤，通过查看DataTable里的GetAssetRegistryTags方法就可以知道它主动提供了RowStructure的Tags注册。
+
+```cpp
+FAssetDataTagMapBase=TSortedMap<FName, FString, FDefaultAllocator, FNameFastLess>; 
+
+SPropertyEditorAsset::
+	/** Tags (and eventually values) that can NOT be used with this property */
+	TSharedPtr<FAssetDataTagMap> DisallowedAssetDataTags;
+
+	**/** Tags and values that must be present for an asset to be used with this property */
+	TSharedPtr<FAssetDataTagMap> RequiredAssetDataTags;
+	
+void SPropertyEditorAsset::InitializeAssetDataTags(const FProperty* Property)
+{
+	if (Property == nullptr)
+{
+	return;
+}
+
+const FProperty* MetadataProperty = GetActualMetadataProperty(Property);
+const FString DisallowedAssetDataTagsFilterString = MetadataProperty->GetMetaData("DisallowedAssetDataTags");
+if (!DisallowedAssetDataTagsFilterString.IsEmpty())
+{
+	TArray<FString> DisallowedAssetDataTagsAndValues;
+	DisallowedAssetDataTagsFilterString.ParseIntoArray(DisallowedAssetDataTagsAndValues, TEXT(","), true);
+
+	for (const FString& TagAndOptionalValueString : DisallowedAssetDataTagsAndValues)
+	{
+		TArray<FString> TagAndOptionalValue;
+		TagAndOptionalValueString.ParseIntoArray(TagAndOptionalValue, TEXT("="), true);
+		size_t NumStrings = TagAndOptionalValue.Num();
+		check((NumStrings == 1) || (NumStrings == 2)); // there should be a single '=' within a tag/value pair
+
+		if (!DisallowedAssetDataTags.IsValid())
+		{
+			DisallowedAssetDataTags = MakeShared<FAssetDataTagMap>();
+		}
+		DisallowedAssetDataTags->Add(FName(*TagAndOptionalValue[0]), (NumStrings > 1) ? TagAndOptionalValue[1] : FString());
+	}
+}
+
+const FString RequiredAssetDataTagsFilterString = MetadataProperty->GetMetaData("RequiredAssetDataTags");
+if (!RequiredAssetDataTagsFilterString.IsEmpty())
+{
+	TArray<FString> RequiredAssetDataTagsAndValues;
+	RequiredAssetDataTagsFilterString.ParseIntoArray(RequiredAssetDataTagsAndValues, TEXT(","), true);
+
+	for (const FString& TagAndOptionalValueString : RequiredAssetDataTagsAndValues)
+	{
+		TArray<FString> TagAndOptionalValue;
+		TagAndOptionalValueString.ParseIntoArray(TagAndOptionalValue, TEXT("="), true);
+		size_t NumStrings = TagAndOptionalValue.Num();
+		check((NumStrings == 1) || (NumStrings == 2)); // there should be a single '=' within a tag/value pair
+
+		if (!RequiredAssetDataTags.IsValid())
+		{
+			RequiredAssetDataTags = MakeShared<FAssetDataTagMap>();
+		}
+		RequiredAssetDataTags->Add(FName(*TagAndOptionalValue[0]), (NumStrings > 1) ? TagAndOptionalValue[1] : FString());
+	}
+}
+}
+
+bool SPropertyEditorAsset::IsAssetFiltered(const FAssetData& InAssetData)
+{
+//判断只要包含就不符合
+	if (DisallowedAssetDataTags.IsValid())
+	{
+		for (const auto& DisallowedTagAndValue : *DisallowedAssetDataTags.Get())
+		{
+			if (InAssetData.TagsAndValues.ContainsKeyValue(DisallowedTagAndValue.Key, DisallowedTagAndValue.Value))
+			{
+				return true;
+			}
+		}
+	}
+	//判断必须包含才不会被过滤掉
+	if (RequiredAssetDataTags.IsValid())
+	{
+		for (const auto& RequiredTagAndValue : *RequiredAssetDataTags.Get())
+		{
+			if (!InAssetData.TagsAndValues.ContainsKeyValue(RequiredTagAndValue.Key, RequiredTagAndValue.Value))
+			{
+				// For backwards compatibility compare against short name version of the tag value.
+				if (!FPackageName::IsShortPackageName(RequiredTagAndValue.Value) &&
+					InAssetData.TagsAndValues.ContainsKeyValue(RequiredTagAndValue.Key, FPackageName::ObjectPathToObjectName(RequiredTagAndValue.Value)))
+				{
+					continue;
+				}
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+void UDataTable::GetAssetRegistryTags(FAssetRegistryTagsContext Context) const
+{
+	if (AssetImportData)
+	{
+		Context.AddTag( FAssetRegistryTag(SourceFileTagName(), AssetImportData->GetSourceData().ToJson(), FAssetRegistryTag::TT_Hidden) );
+	}
+
+	// Add the row structure tag
+	{
+		static const FName RowStructureTag = "RowStructure";
+		Context.AddTag( FAssetRegistryTag(RowStructureTag, GetRowStructPathName().ToString(), FAssetRegistryTag::TT_Alphabetical) );
+	}
+
+	Super::GetAssetRegistryTags(Context);
+}
+
+```