This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(153.6, 16%, 24%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ETT%3C/text%3E%3C/svg%3E)
I'm trying to add a settings page to my existing WinUI 3 app using Template Studio (With Navigation Bar) with the MVVM pattern. However, I'm encountering the following error:
System.Exception: Error executing 'Microsoft.Templates.Core.PostActions.Catalog.Merge.MergePostAction'. Related template: ts.WinUI.MVVMToolkit.Feat.ThemeSelection. ---> System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at Microsoft.Templates.Core.PostActions.Catalog.Merge.MergeHandler.FindAndModifyContextLine(String mergeLine, Int32 diffTrivia)
at Microsoft.Templates.Core.PostActions.Catalog.Merge.MergeHandler.Merge(IEnumerable`1 source, IEnumerable`1 merge)
at Microsoft.Templates.Core.PostActions.Catalog.Merge.MergePostAction.ExecuteInternal()
at Microsoft.Templates.Core.PostActions.PostAction.Execute()
--- End of inner exception stack trace ---
at Microsoft.Templates.Core.PostActions.PostAction.Execute()
at Microsoft.Templates.Core.Gen.GenController.ExecutePostActions(GenInfo genInfo, ITemplateCreationResult generationResult)
at Microsoft.Templates.Core.Gen.GenController.<GenerateItemsAsync>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Templates.Core.Gen.NewItemGenController.<UnsafeGenerateNewItemAsync>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Templates.UI.Services.GenerationService.<GenerateNewItemAsync>d__6.MoveNext()
This is the problem i faced
I've tried the following steps:
Checked the App.xaml.cs and theme-related files for any discrepancies.
However, the issue persists. Could someone please help me resolve this error?
Hello @TUAN THANH VO ,
Welcome to Microsoft Q&A!
Your screenshot seems to be different from my Template Studio for WinUI (C#). Which extension are you using?
Please make sure that the environment required by WinUI3 project, especially Windows.APP.SDK is correctly installed.
Thank you.
@Junjie Zhu - MSFT
Thank you for answering my question.
As I mentioned, I am adding a Settings Page to an existing WinUI3 application through Template Studio, not during the initial setup with Template Studio. When I create a new application, it works the same as yours. However, since I didn’t add the Settings Page at the time of creation, I am now unable to add it due to the aforementioned error. That said, I can still add a blank page. I think this issue occurs because Template Studio cannot merge my existing code with the code generated when creating the Settings Page.
Hello @TUAN THANH VO ,
I got it, I tried it and successfully added a new Settings page. I suggest you reinstall the extension or Visual studio. If it still doesn't work, I suggest you submit this issue on https://github.com/microsoft/TemplateStudio/issues.