您应该在"首选项">"项目">"SDK位置">"苹果">"Xamarin.iOS SDK"框中放入什么？
当我把它留空时，我会得到一个绿色复选框，上面写着它找到了位置。然而，当我尝试打开一个项目时，我得到：
System.NotSupportedException: Could not parse iOS version from SDK path: Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk
at MonoTouch.Hosting.IosSystem..ctor (System.String sdkPath, DeviceTrait device, MonoTouch.Hosting.Capabilities capabilities) [0x000f4] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Hosting/IosSystem.cs:184
at MonoTouch.Hosting.IosSystem..ctor (System.String sdkPath, DeviceTrait device) [0x00000] in <filename unknown>:0
at MonoTouch.Design.Client.PooledConnectionProvider+<GetConnection>c__AnonStorey51.<>m__10B () [0x00021] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/Connection/PooledConnectionProvider.cs:33
at MonoTouch.Design.Client.PooledConnectionProvider+Pool.Acquire () [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/Connection/PooledConnectionProvider.cs:97
at MonoTouch.Design.Client.PooledConnectionProvider+Pool..ctor (Int32 count, System.Func`1 acquire) [0x00020] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/Connection/PooledConnectionProvider.cs:81
at MonoTouch.Design.Client.PooledConnectionProvider.GetConnection (DeviceTrait device) [0x0003d] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/Connection/PooledConnectionProvider.cs:29
at MonoTouch.Design.Client.IPhoneDesignerService.PrefillConnectionPool (System.String sdkPath, TargetDevice projectTargetDevice) [0x0001a] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/IPhoneDesignerService.cs:82
at MonoTouch.Design.Client.IPhoneDesignerService.IncrementOpenProjectCount (System.String sdkPath, Int32 projectTargetDevice) [0x0004c] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/Xamarin.Designer.iOS/MonoTouch.Design.Client/IPhoneDesignerService.cs:102
at MonoDevelop.IPhone.IPhoneProject.OnEndLoad () [0x0003c] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/md-addins/MonoDevelop.IPhone/MonoDevelop.IPhone/Project/IPhoneProject.cs:275
at MonoDevelop.Projects.SolutionItem.MonoDevelop.Projects.ILoadController.EndLoad () [0x0000e] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/SolutionItem.cs:877
at MonoDevelop.Projects.Extensions.LoadOperation.End () [0x00019] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.Extensions/ProjectExtensionUtil.cs:138
at MonoDevelop.Projects.Extensions.ProjectExtensionUtil.EndLoadOperation () [0x00042] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.Extensions/ProjectExtensionUtil.cs:85
at MonoDevelop.Projects.Formats.MSBuild.SlnFileFormat.ReadFile (System.String fileName, MonoDevelop.Projects.Formats.MSBuild.MSBuildFileFormat format, IProgressMonitor monitor) [0x0006e] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.Formats.MSBuild/SlnFileFormat.cs:652
at MonoDevelop.Projects.Formats.MSBuild.MSBuildFileFormat.ReadFile (FilePath file, System.Type expectedType, IProgressMonitor monitor) [0x00017] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.Formats.MSBuild/MSBuildFileFormat.cs:166
at MonoDevelop.Projects.ProjectService.ReadFile (IProgressMonitor monitor, System.String file, System.Type expectedType, MonoDevelop.Projects.FileFormat& format) [0x0002d] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs:310
at MonoDevelop.Projects.ProjectService.InternalReadWorkspaceItem (System.String file, IProgressMonitor monitor) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs:282
at MonoDevelop.Projects.DefaultProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs:677
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Autotools.MakefileProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/addins/MonoDevelop.Autotools/MakefileProjectServiceExtension.cs:48
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectServiceExtension.LoadWorkspaceItem (IProgressMonitor monitor, System.String fileName) [0x00000] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs:108
at MonoDevelop.Projects.ProjectService.ReadWorkspaceItem (IProgressMonitor monitor, System.String file) [0x00027] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs:261
at MonoDevelop.Ide.RootWorkspace.BackgroundLoadWorkspace (IProgressMonitor monitor, System.String filename, Boolean loadPreferences, Boolean reloading) [0x00163] in /Users/builder/data/lanes/monodevelop_private-lion-splash2/33f01126/source/monodevelop/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide/RootWorkspace.cs:593
您可能安装了损坏的Xcode，需要（卸载后）重新安装。请尝试将其更改为/Developer/MonoTouch/，看看是否有效。我试过了，也把它留空，他们都给了我一个绿色箭头，允许我打开一个项目。
编辑：我认为这是Xcode/iOS SDK安装的问题，而不是Xamarin.iOS安装的问题。如果您将"显示内容"到您正在引用的Xcode.app，然后导航到：/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/，那么您应该会看到一个iOS特定的sdk文件夹。我的名字是：iPhoneSimulator6.1.sdk。我不确定它用来解析iOS版本的确切方法，但应该有一个SDKSettings.plist文件，其中有一个"版本"条目。这对我来说似乎是最合乎逻辑的。