我有一个用 C# 编写的 Xamarin iOS 项目。我已经实现了一个UIDocumentPickerViewController可以将外部文件导入我的应用程序。PDF 和 XML 在 iOS 11 上的工作就像一个魅力，代码如下：
// Allow the Document picker to select a range of document types
var allowedUTIs = new string[] {
UTType.PDF,
UTType.XML,
"com.recordare.musicxml",
"com.recordare.musicxml.uncompressed",
"public.data",
"public.mxl",
"public.content"
};
UIDocumentPickerViewController picker = new UIDocumentPickerViewController(allowedUTIs, UIDocumentPickerMode.Import);
但是.mxl文件，即 MusicXML 文件在文件应用程序（DocumentPicker 视图）中显示为灰色。
在我的 Info.plist 文件中，我有以下文档类型：
以及进口的尿路感染：
我在 Google 上搜索了 MusicXML 社区声明的官方 UTI。在他们的网站上，我只发现了关于提议的 UTI 的讨论，说明如下： https ://forums.makemusic.com/viewtopic.php?f=12&t=2510
附件是一个 XML 文件（也在此电子邮件的底部），其中包含基于 Apple 文档中提供的信息的 MusicXML 的 UTI 声明提案。我们使用了以下类型标识符： 未压缩的 MusicXML：com.musicxml.musicxml 压缩的 MusicXML：com.musicxml.musicxml-compressed
我还在我的 Info.plist 中尝试了这 2 个 UTI（com.musicxml.musicxml、com.musicxml.musicxml-compressed）。仍然没有用。
任何人都可以帮助我吗？
编辑 1： 在这里您可以看到整个 Info.plist 文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>UTImportedTypeDeclarations</key>
<array>
<dict>
<key>UTTypeIdentifier</key>
<string>com.recordare.musicxml.uncompressed</string>
<key>UTTypeReferenceURL</key>
<string>http://www.musicxml.org/</string>
<key>UTTypeDescription</key>
<string>MusicXML</string>
<key>UTTypeTagSpecification</key>
<dict>
<key>public.filename-extension</key>
<array>
<string>xml</string>
</array>
<key>public.mime-type</key>
<array>
<string>application/vnd.recordare.musicxml+xml</string>
</array>
</dict>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
</dict>
<dict>
<key>UTTypeIdentifier</key>
<string>com.recordare.musicxml</string>
<key>UTTypeReferenceURL</key>
<string>http://www.musicxml.org/</string>
<key>UTTypeDescription</key>
<string>MusicXML</string>
<key>UTTypeTagSpecification</key>
<dict>
<key>public.filename-extension</key>
<array>
<string>mxl</string>
</array>
<key>public.mime-type</key>
<array>
<string>application/vnd.recordare.musicxml</string>
</array>
</dict>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
</dict>
<dict>
<key>UTTypeDescription</key>
<string>Midi</string>
<key>UTTypeTagSpecification</key>
<dict>
<key>public.filename-extension</key>
<array>
<string>mid</string>
</array>
<key>public.mime-type</key>
<array>
<string>audio/midi</string>
</array>
</dict>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeIdentifier</key>
<string>public.data</string>
</dict>
</array>
<key>CFBundleDocumentTypes</key>
<array>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>public.xml</string>
</array>
<key>CFBundleTypeName</key>
<string>MusicSheet</string>
</dict>
<dict>
<key>CFBundleTypeIconFiles</key>
<array/>
<key>CFBundleTypeName</key>
<string>MusicSheet</string>
<key>LSItemContentTypes</key>
<array>
<string>com.recordare.musicxml</string>
</array>
</dict>
<dict>
<key>CFBundleTypeIconFiles</key>
<array/>
<key>CFBundleTypeName</key>
<string>MusicSheet</string>
<key>LSItemContentTypes</key>
<array>
<string>com.recordare.musicxml.uncompressed</string>
</array>
</dict>
<dict>
<key>CFBundleTypeName</key>
<string>PDF</string>
<key>LSItemContentTypes</key>
<array>
<string>com.adobe.pdf</string>
</array>
</dict>
<dict>
<key>CFBundleTypeName</key>
<string>Midi</string>
<key>LSItemContentTypes</key>
<array>
<string>public.data</string>
</array>
</dict>
</array>
<key>MinimumOSVersion</key>
<string>9.3</string>
<key>UIAppFonts</key>
<array>
<string>Fonts/companySymbols.ttf</string>
<string>Fonts/webhostinghub-glyphs.ttf</string>
</array>
<key>UIDeviceFamily</key>
<array>
<integer>1</integer>
<integer>2</integer>
</array>
<key>UISupportedInterfaceOrientations~ipad</key>
<array>
<string>UIInterfaceOrientationPortrait</string>
<string>UIInterfaceOrientationPortraitUpsideDown</string>
<string>UIInterfaceOrientationLandscapeLeft</string>
<string>UIInterfaceOrientationLandscapeRight</string>
</array>
<key>CFBundleIdentifier</key>
<string>com.company.test1</string>
<key>XSAppIconAssets</key>
<string>Resources/Images.xcassets/AppIcons.appiconset</string>
<key>CFBundleShortVersionString</key>
<string>1.2.0</string>
<key>CFBundleName</key>
<string>Test1</string>
<key>UISupportedInterfaceOrientations</key>
<array>
<string>UIInterfaceOrientationPortrait</string>
<string>UIInterfaceOrientationPortraitUpsideDown</string>
<string>UIInterfaceOrientationLandscapeLeft</string>
<string>UIInterfaceOrientationLandscapeRight</string>
</array>
<key>UILaunchStoryboardName</key>
<string>LaunchScreen</string>
<key>NSMicrophoneUsageDescription</key>
<string>microphone use</string>
<key>CFBundleDisplayName</key>
<string>Test1</string>
<key>UIViewControllerBasedStatusBarAppearance</key>
<false/>
<key>XSLaunchImageAssets</key>
<string>Resources/Images.xcassets/LaunchImage.launchimage</string>
<key>CFBundleVersion</key>
<string>16</string>
<key>LSApplicationQueriesSchemes</key>
<array>
<string>fb-messenger-api</string>
<string>fbauth2</string>
</array>
<key>CFBundleURLTypes</key>
<array>
<dict>
<key>CFBundleURLName</key>
<string>com.company.test1</string>
<key>CFBundleURLSchemes</key>
<array>
<string>fb899828993298981</string>
<string>com.company.test1</string>
<string>com.googleusercontent.apps.989898989981191-232111s4lsf441cu94</string>
</array>
<key>CFBundleURLTypes</key>
<string>Viewer</string>
</dict>
</array>
</dict>
</plist>