Mac版Visual Studio无法预览Android界面问题求助

I've run into similar glitches with the Xamarin Android Designer in VS for Mac before, so here are some practical steps to work through this System.NullReferenceException:

• Clean & Rebuild Your Solution
  Start with the basics: right-click your project → Clean, then right-click again → Rebuild. Compilation cache quirks often cause the designer to fail parsing code correctly, and a clean rebuild resets this state.

• Update Visual Studio & Xamarin Components
  This error traces back to the CodeModelBridge in the Xamarin Android Designer, which is a known issue in older versions. Open Visual Studio for Mac, go to Visual Studio → Check for Updates, and install all available stable updates for Visual Studio, Xamarin.Android, and Android SDK tools.

• Verify Your Activity Class Definitions
  The error fires when the designer checks if a type is an Activity (IsActivityType method). Double-check your Activity classes:

  • Make sure they properly inherit from AppCompatActivity or Activity
  • Fix any syntax errors, missing using directives, or invalid custom attributes/annotations that might break code analysis
  • Confirm all referenced NuGet packages (like Xamarin.Forms if you're using it) are installed correctly

• Reset the Designer Cache
  Corrupted designer cache files can cause this crash. Here's how to clear them:

  1. Close Visual Studio for Mac completely
  2. Open Finder, press Cmd+Shift+G, and paste this path (replace [VS_Version] with your installed version, e.g., 17.0):

     ~/Library/Caches/VisualStudio/[VS_Version]/Xamarin/AndroidDesigner
     

  3. Delete all files and folders in this directory
  4. Reopen Visual Studio and try the preview again

• Test with a Fresh Project
  Create a new blank Android project and check if the preview works there. If it does, the problem is specific to your current project—gradually migrate code from your broken project to the new one to identify which part is causing the error.

Original Error Stack Trace: #

System.NullReferenceException: Object reference not set to an instance of an object
at Xamarin.AndroidDesigner.CodeInteractions.CodeModelBridge.b__31_0 (Microsoft.CodeAnalysis.AttributeData a) [0x00000] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner.CodeInteractions/CodeModelBridge.cs:403
at System.Linq.ImmutableArrayExtensions.Any[T] (System.Collections.Immutable.ImmutableArray`1[T] immutableArray, System.Func`2[T,TResult] predicate) [0x00025] in <36486b016d234fca8cd67892bf29c7b5>:0
at Xamarin.AndroidDesigner.CodeInteractions.CodeModelBridge.IsActivityType (Microsoft.CodeAnalysis.INamedTypeSymbol type) [0x00008] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner.CodeInteractions/CodeModelBridge.cs:403
at Xamarin.AndroidDesigner.CodeInteractions.CodeModelBridge.GetAndroidEntityForType (Microsoft.CodeAnalysis.INamedTypeSymbol type) [0x00001] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner.CodeInteractions/CodeModelBridge.cs:120
at Xamarin.AndroidDesigner.CodeInteractions.CodeModelBridge.b__26_2 (Microsoft.CodeAnalysis.INamedTypeSymbol t) [0x00000] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner.CodeInteractions/CodeModelBridge.cs:311
at System.Linq.Utilities+<>c__DisplayClass1_0`1[TSource].<CombinePredicates>b__0 (TSource x) [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.Linq/src/System/Linq/Utilities.cs:58
at System.Linq.Enumerable+WhereSelectEnumerableIterator`2[TSource,TResult].ToList () [0x0001b] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.Linq/src/System/Linq/Where.cs:737
at System.Linq.Enumerable.ToList[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x0000e] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.Linq/src/System/Linq/ToCollection.cs:30
at Xamarin.AndroidDesigner.CodeInteractions.CodeModelBridge+<GetCustomComponentsInProject>d__26.MoveNext () [0x00147] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner.CodeInteractions/CodeModelBridge.cs:308
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00037] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:357
at Xamarin.AndroidDesigner.DesignerProject+d__101.MoveNext () [0x00025] in /Users/vsts/agent/2.133.3/work/1/s/Xamarin.Designer.Android/Xamarin.AndroidDesigner/Xamarin.AndroidDesigner/DesignerProject.cs:300
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00037] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in /Users/builder/jenkins/workspace/build-package-osx-mono/2018-02/external/bockbuild/builds/mono-x64/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156

内容的提问来源于stack exchange，提问作者AppsThatFly