In a UWP application using WebView2, the CoreWebView2 method returns null after changing the region at runtime in C#

Jay 100

The CoreWebView2 method works fine the first time, but after changing the app region, the CoreWebView2 method returns null after initialization. Please help to fix this issue.

Code:

XAML

 <muxc:WebView2 x:Name="PDFViewer" NavigationStarting="PDFViewer_NavigationStarting" Margin="0" 
                NavigationCompleted="PDFViewer_NavigationCompleted" Visibility="Visible"/>

CS file

PDFViewer.CoreWebView2

await PDFViewer.EnsureCoreWebView2Async();
PDFViewer.CoreWebView2.SetVirtualHostNameToFolderMapping("mi.Pdf", pdfFolder.Path, CoreWebView2HostResourceAccessKind.Allow);

I have change region in below function

Windows.Globalization.ApplicationLanguages.PrimaryLanguageOverride = "en-US";
CultureInfo.DefaultThreadCurrentCulture = culture;
CultureInfo.DefaultThreadCurrentUICulture = culture;
CultureInfo.CurrentCulture = culture;
CultureInfo.CurrentUICulture = culture;

Exception:

User's image

Junjie Zhu - MSFT 18,081 Reputation points Microsoft Vendor

2024-09-04T02:30:17.4966667+00:00

Hi @Jay ,

Welcome to Microsoft Q&A!

I wrote a simple UWP project. After changing the region, coreWebView can still be used normally. Where is PDFViewer.CoreWebView2.SetVirtualHostNameToFolderMapping used? Could you please provide a minimal-reproducible-example to help us further check the problem for you?

Thank you.

Jay 100

Hi @Junjie Zhu - MSFT

Thanks for response

In my project, I created a folder named PDFFiles within LocalState. I store PDF files in the PDFFiles folder and then fetch and display these PDF files in a WebView2 component within the project.

Sample Code:

string installationPath = Package.Current.InstalledLocation.Path;
StorageFolder storageFolder = ApplicationData.Current.LocalFolder;
StorageFolder pdfFolder = await storageFolder.GetFolderAsync("PDFFiles");

await PDFViewer.EnsureCoreWebView2Async();
PDFViewer.CoreWebView2.SetVirtualHostNameToFolderMapping("mi.Pdf", pdfFolder.Path, CoreWebView2HostResourceAccessKind.Allow);
PDFViewer.Source = new Uri($"https://mi.Pdf/{invoicePDFfile.Name}#view=FitH&toolbar=0");

Notes: It’s working fine, but after I change the region, CoreWebView2 returns null.

Junjie Zhu - MSFT 18,081 Reputation points Microsoft Vendor

2024-09-05T09:42:07.15+00:00

Hi @Jay ,

I used your code and still can't reproduce the same behavior, it works fine. Could you please try to test with a different device? Or try this in a blank UWP project to see if you can reproduce the same behavior.

Thank you.
Jay 100 Reputation points

2024-09-05T11:30:45.7366667+00:00

Hi @Junjie Zhu - MSFT

Sure, let me check with different devices.
Jay 100 Reputation points

2024-09-05T11:56:17.0466667+00:00

Hi @Junjie Zhu - MSFT

I have checked with a fresh UWP and tested it, and it’s working fine. I’m not sure why it’s not working in my current project.
Junjie Zhu - MSFT 18,081 Reputation points Microsoft Vendor

2024-09-06T07:24:35.9933333+00:00

Hi @Jay ,

This is difficult to find the error, maybe you can try to update or reinstall WebView2 in NuGet Manager.
Roy Li - MSFT 33,366 Reputation points Microsoft Vendor

2024-09-10T02:30:02.97+00:00

Haven't heard from you for a while. Any updates about this issue?
Jay 100 Reputation points

2024-09-10T12:49:29.4233333+00:00

Hi @Roy Li - MSFT

I checked this issue by reinstalling WebView2 using the NuGet Manager as suggested by @Junjie Zhu - MSFT , but I am still facing the same problem. I have not found any solution for this issue yet.
Junjie Zhu - MSFT 18,081 Reputation points Microsoft Vendor

2024-09-13T07:01:32.3466667+00:00

Hi @Jay ,

This unexpected behavior is more related to WebView2 itself. If the behavior only occurs on a single device, we recommend that you submit this behavior at WebView2Feedback.

Thank you.
Jay 100 Reputation points

2024-09-16T06:54:08.93+00:00

Hi @Junjie Zhu - MSFT

Issue resolved: It works when we set the application region in the App.xaml.cs or ExtendedSplash.xaml.cs files.

Thank you.

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Jay 100 Reputation points

2024-09-16T06:54:26.4933333+00:00

Issue resolved: It works when we set the application region in the App.xaml.cs or ExtendedSplash.xaml.cs files.
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In a UWP application using WebView2, the CoreWebView2 method returns null after changing the region at runtime in C#

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