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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Path/ContentDir/ContentDir.md

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+# ContentDir
+
+- **功能描述：** 使用UE的风格来选择Content以及子目录。
+- **使用位置：** UPROPERTY
+- **引擎模块：** Path Property
+- **元数据类型：** bool
+- **限制类型：** FDirectoryPath
+- **关联项：** [RelativePath](../RelativePath.md), [RelativeToGameContentDir](../RelativeToGameContentDir.md)
+- **常用程度：** ★★★
+
+使用UE的风格来选择Content以及子目录。
+
+默认情况下，选择一个目录，会弹出windows默认的选择目录对话框，因为FDirectoryPath 你确实可以用来选择到windows系统里任意的目录（可能你的项目就是这么需求的）。但如果你确实就是想要选择一个UE Content下目录，这个时候你指定ContentDir，UE就可以为你弹出一个专门的UE选择目录对话框，更加的便利也避免出错。
+
+在使用FDirectoryPath的时候，ContentDir和LongPackageName是等价的。
+
+## 测试代码：
+
+```cpp
+UCLASS(BlueprintType)
+class INSIDER_API UMyProperty_Path :public UObject
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DirectoryPath)
+	FDirectoryPath MyDirectory_Default;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DirectoryPath, meta = (ContentDir))
+	FDirectoryPath MyDirectory_ContentDir;
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DirectoryPath, meta = (LongPackageName))
+	FDirectoryPath MyDirectory_LongPackageName;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DirectoryPath, meta = (RelativeToGameContentDir))
+	FDirectoryPath MyDirectory_RelativeToGameContentDir;
+
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = DirectoryPath, meta = (RelativePath))
+	FDirectoryPath MyDirectory_RelativePath;
+};
+
+```
+
+## 测试结果：
+
+- 默认的MyDirectory_Default会打开系统对话框，可以选择任何目录。
+- MyDirectory_ContentDir和MyDirectory_LongPackageName，会如图所示弹出UE风格的对话框来选择目录。
+- MyDirectory_RelativeToGameContentDir和MyDirectory_RelativePath都会弹出系统对话框，不同的是MyDirectory_RelativeToGameContentDir最终的目录会限制在Content目录下（如果选择别的目录，会弹出错误警告），结果是个相对路径。MyDirectory_RelativePath的结果也是个相对路径，但是可以选择任意目录。
+
+![Untitled](Untitled.png)
+
+## 原理：
+
+FDirectoryPath的编辑有FDirectoryPathStructCustomization来定制化。根据其代码可见，如果有ContentDir或LongPackageName，则则是个ContentDir，则会采用OnPickContent来选择目录。内部再用ContentBrowserModule.Get().CreatePathPicker(PathPickerConfig)来创建专门的目录选择菜单。
+
+否则走到OnPickDirectory分支，会采用DesktopPlatform->OpenDirectoryDialog来打开系统的对话框。
+
+从源码也可以看出：
+
+bRelativeToGameContentDir会导致Directory.RightChopInline(AbsoluteGameContentDir.Len(), EAllowShrinking::No);， 把Conent路径的左边部分切掉。
+
+bUseRelativePath会触发Directory = IFileManager::Get().ConvertToRelativePath(*Directory);，把路径转换成相对路径。
+
+```cpp
+/** Structure for directory paths that are displayed in the editor with a picker UI. */
+USTRUCT(BlueprintType)
+struct FDirectoryPath
+{
+	GENERATED_BODY()
+
+	/**
+	* The path to the directory.
+	*/
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = Path)
+	FString Path;
+};
+
+RegisterCustomPropertyTypeLayout("DirectoryPath", FOnGetPropertyTypeCustomizationInstance::CreateStatic(&FDirectoryPathStructCustomization::MakeInstance));
+RegisterCustomPropertyTypeLayout("FilePath", FOnGetPropertyTypeCustomizationInstance::CreateStatic(&FFilePathStructCustomization::MakeInstance));
+	
+void FDirectoryPathStructCustomization::CustomizeHeader( TSharedRef<IPropertyHandle> StructPropertyHandle, class FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& StructCustomizationUtils )
+{
+	TSharedPtr<IPropertyHandle> PathProperty = StructPropertyHandle->GetChildHandle("Path");
+
+	const bool bRelativeToGameContentDir = StructPropertyHandle->HasMetaData( TEXT("RelativeToGameContentDir") );
+	const bool bUseRelativePath = StructPropertyHandle->HasMetaData( TEXT("RelativePath") );
+	const bool bContentDir = StructPropertyHandle->HasMetaData( TEXT("ContentDir") ) || StructPropertyHandle->HasMetaData(TEXT("LongPackageName"));
+	
+	AbsoluteGameContentDir = FPaths::ConvertRelativePathToFull(FPaths::ProjectContentDir());
+	
+	if(bContentDir)
+	{
+		PickerWidget = SAssignNew(PickerButton, SButton)
+		.ButtonStyle( FAppStyle::Get(), "HoverHintOnly" )
+		.ToolTipText( LOCTEXT( "FolderComboToolTipText", "Choose a content directory") )
+		.OnClicked( this, &FDirectoryPathStructCustomization::OnPickContent, PathProperty.ToSharedRef() )
+		.ContentPadding(2.0f)
+		.ForegroundColor( FSlateColor::UseForeground() )
+		.IsFocusable(false)
+		.IsEnabled(this, &FDirectoryPathStructCustomization::IsBrowseEnabled, StructPropertyHandle)
+		[
+			SNew(SImage)
+			.Image(FAppStyle::GetBrush("PropertyWindow.Button_Ellipsis"))
+			.ColorAndOpacity(FSlateColor::UseForeground())
+		];
+	
+	}
+	else
+	{
+		PickerWidget = SAssignNew(BrowseButton, SButton)
+		.ButtonStyle( FAppStyle::Get(), "HoverHintOnly" )
+		.ToolTipText( LOCTEXT( "FolderButtonToolTipText", "Choose a directory from this computer") )
+		.OnClicked( this, &FDirectoryPathStructCustomization::OnPickDirectory, PathProperty.ToSharedRef(), bRelativeToGameContentDir, bUseRelativePath )
+		.ContentPadding( 2.0f )
+		.ForegroundColor( FSlateColor::UseForeground() )
+		.IsFocusable( false )
+		.IsEnabled( this, &FDirectoryPathStructCustomization::IsBrowseEnabled, StructPropertyHandle )
+		[
+			SNew( SImage )
+			.Image( FAppStyle::GetBrush("PropertyWindow.Button_Ellipsis") )
+			.ColorAndOpacity( FSlateColor::UseForeground() )
+		];
+	}
+}
+
+FReply FDirectoryPathStructCustomization::OnPickContent(TSharedRef<IPropertyHandle> PropertyHandle) 
+{
+	FContentBrowserModule& ContentBrowserModule = FModuleManager::LoadModuleChecked<FContentBrowserModule>("ContentBrowser");
+	FPathPickerConfig PathPickerConfig;
+	PropertyHandle->GetValue(PathPickerConfig.DefaultPath);
+	PathPickerConfig.bAllowContextMenu = false;
+	PathPickerConfig.OnPathSelected = FOnPathSelected::CreateSP(this, &FDirectoryPathStructCustomization::OnPathPicked, PropertyHandle);
+
+	FMenuBuilder MenuBuilder(true, NULL);
+	MenuBuilder.AddWidget(SNew(SBox)
+		.WidthOverride(300.0f)
+		.HeightOverride(300.0f)
+		[
+			ContentBrowserModule.Get().CreatePathPicker(PathPickerConfig)
+		], FText());
+
+	PickerMenu = FSlateApplication::Get().PushMenu(PickerButton.ToSharedRef(),
+		FWidgetPath(),
+		MenuBuilder.MakeWidget(),
+		FSlateApplication::Get().GetCursorPos(),
+		FPopupTransitionEffect(FPopupTransitionEffect::ContextMenu)
+		);
+
+	return FReply::Handled();
+}
+
+FReply FDirectoryPathStructCustomization::OnPickDirectory(TSharedRef<IPropertyHandle> PropertyHandle, const bool bRelativeToGameContentDir, const bool bUseRelativePath) const
+{
+	FString Directory;
+	IDesktopPlatform* DesktopPlatform = FDesktopPlatformModule::Get();
+	if (DesktopPlatform)
+	{
+
+		TSharedPtr<SWindow> ParentWindow = FSlateApplication::Get().FindWidgetWindow(BrowseButton.ToSharedRef());
+		void* ParentWindowHandle = (ParentWindow.IsValid() && ParentWindow->GetNativeWindow().IsValid()) ? ParentWindow->GetNativeWindow()->GetOSWindowHandle() : nullptr;
+
+		FString StartDirectory = FEditorDirectories::Get().GetLastDirectory(ELastDirectory::GENERIC_IMPORT);
+		if (bRelativeToGameContentDir && !IsValidPath(StartDirectory, bRelativeToGameContentDir))
+		{
+			StartDirectory = AbsoluteGameContentDir;
+		}
+
+		// Loop until; a) the user cancels (OpenDirectoryDialog returns false), or, b) the chosen path is valid (IsValidPath returns true)
+		for (;;)
+		{
+			if (DesktopPlatform->OpenDirectoryDialog(ParentWindowHandle, LOCTEXT("FolderDialogTitle", "Choose a directory").ToString(), StartDirectory, Directory))
+			{
+				FText FailureReason;
+				if (IsValidPath(Directory, bRelativeToGameContentDir, &FailureReason))
+				{
+					FEditorDirectories::Get().SetLastDirectory(ELastDirectory::GENERIC_IMPORT, Directory);
+
+					if (bRelativeToGameContentDir)
+					{
+						Directory.RightChopInline(AbsoluteGameContentDir.Len(), EAllowShrinking::No);
+					}
+					else if (bUseRelativePath)
+					{
+						Directory = IFileManager::Get().ConvertToRelativePath(*Directory);
+					}
+
+					PropertyHandle->SetValue(Directory);
+				}
+				else
+				{
+					StartDirectory = Directory;
+					FMessageDialog::Open(EAppMsgType::Ok, FailureReason);
+					continue;
+				}
+			}
+			break;
+		}
+	}
+
+	return FReply::Handled();
+}
+
+```