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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/DetailsPanel/bShowOnlyWhenTrue/bShowOnlyWhenTrue.md

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+# bShowOnlyWhenTrue
+
+- **功能描述：** 根据编辑器config配置文件里字段值来决定当前属性是否显示。
+- **使用位置：** UPROPERTY
+- **引擎模块：** DetailsPanel
+- **元数据类型：** string="abc"
+- **常用程度：** ★
+
+根据编辑器config配置文件里字段值来决定当前属性是否显示。
+
+- 这个编辑器config配置文件，指的是GEditorPerProjectIni，因此一般是Config\DefaultEditorPerProjectUserSettings.ini
+- 其中Section的名字是“UnrealEd.PropertyFilters”
+- 然后Key的值就可以定了。
+
+在源码里没有找到使用的例子，但这依然是可以工作的。
+
+## 测试代码：
+
+```cpp
+D:\github\GitWorkspace\Hello\Config\DefaultEditorPerProjectUserSettings.ini
+[UnrealEd.PropertyFilters]
+ShowMyInt=true
+ShowMyString=false
+
+UCLASS(BlueprintType)
+class INSIDER_API UMyProperty_Show :public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite)
+	int32 MyInt = 123;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (bShowOnlyWhenTrue = "ShowMyInt"))
+	int32 MyInt_WithShowOnly = 123;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, meta = (bShowOnlyWhenTrue = "ShowMyString"))
+	FString MyString_WithShowOnly;
+};
+```
+
+## 测试结果：
+
+可见MyString_WithShowOnly就没有显示出来，因为我们在DefaultEditorPerProjectUserSettings中配置了ShowMyString=false。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+就是取得config中的值用来决定属性框是否显示。
+
+```cpp
+void FObjectPropertyNode::GetCategoryProperties(const TSet<UClass*>& ClassesToConsider, const FProperty* CurrentProperty, bool bShouldShowDisableEditOnInstance, bool bShouldShowHiddenProperties,
+	const TSet<FName>& CategoriesFromBlueprints, TSet<FName>& CategoriesFromProperties, TArray<FName>& SortedCategories)
+{
+	bool bMetaDataAllowVisible = true;
+	const FString& ShowOnlyWhenTrueString = CurrentProperty->GetMetaData(Name_bShowOnlyWhenTrue);
+	if (ShowOnlyWhenTrueString.Len())
+	{
+		//ensure that the metadata visibility string is actually set to true in order to show this property
+		GConfig->GetBool(TEXT("UnrealEd.PropertyFilters"), *ShowOnlyWhenTrueString, bMetaDataAllowVisible, GEditorPerProjectIni);
+	}
+	
+	if (bMetaDataAllowVisible)
+	{
+		if (PropertyEditorHelpers::ShouldBeVisible(*this, CurrentProperty) && !HiddenCategories.Contains(CategoryName))
+		{
+			if (!CategoriesFromBlueprints.Contains(CategoryName) && !CategoriesFromProperties.Contains(CategoryName))
+			{
+				SortedCategories.AddUnique(CategoryName);
+			}
+			CategoriesFromProperties.Add(CategoryName);
+		}
+	}
+
+}
+
+void FCategoryPropertyNode::InitChildNodes()
+{
+		bool bMetaDataAllowVisible = true;
+		if (!bShowHiddenProperties)
+		{
+						static const FName Name_bShowOnlyWhenTrue("bShowOnlyWhenTrue");
+						const FString& MetaDataVisibilityCheckString = It->GetMetaData(Name_bShowOnlyWhenTrue);
+						if (MetaDataVisibilityCheckString.Len())
+						{
+							//ensure that the metadata visibility string is actually set to true in order to show this property
+							// @todo Remove this
+							GConfig->GetBool(TEXT("UnrealEd.PropertyFilters"), *MetaDataVisibilityCheckString, bMetaDataAllowVisible, GEditorPerProjectIni);
+						}
+		}
+
+}
+```