WebView2Loader.dll not found is Outlook VSTO addin - outlook

Question

I read allot about the WebView2Loader.dll - file not found issue, but couldn't solve the problem in my case:
A simple Outlook VSTO add-in with FormRegion,
Inside the FormRegion I placed the WebView2 control, and initialized it:
private async void FormRegionWebView2_FormRegionShowing(object sender, System.EventArgs e)
{
await InitializeCoreWebView2Async(webView2Ctrl, #"C:\temp");
webView2Ctrl.Source = new Uri("http://www.bing.com");
}
public async Task InitializeCoreWebView2Async(WebView2 wv, string webCacheDir)
{
CoreWebView2EnvironmentOptions options = null;
CoreWebView2Environment webView2Environment = null;
webView2Environment = await CoreWebView2Environment.CreateAsync(null, webCacheDir, options);
await wv.EnsureCoreWebView2Async(webView2Environment);
}
The native dlls are in the bin\Debug\runtimes folders,
But I still get 'WebView2Loader.dll': The specified module could not be found' in InitializeCoreWebView2Async()
Here is the code:
https://github.com/MicrosoftEdge/WebView2Feedback/files/8117191/OutlookAddInWithWebView.zip
Any help would be very appreciated.

Answer 1

First of all, make sure the WebView2 Runtime is installed on the system. You can read more about that in the WebView2 Runtime installation section in MSDN.
WebView2Loader.dll is a native and architecture-specific binary, so you need to include all flavors of this binary that you expect your app to run in. For example:
For x86, you would include the x86 version of WebView2Loader.dll.
For a managed app using AnyCPU, you would include the x86, x64, and arm64 versions of WebView2Loader.dll. The correct version of WebView2Loader.dll is loaded from the appropriate architecture-specific folder.
Make sure that you included all the required platform-specific assemblies. Read more about that in the Files to ship with the app article.
BTW I have found a similar issue - Unable to load DLL 'WebView2Loader.dll': The specified module could not be found.. It is very close to what you are describing.

Answer 2

It turns out that Outlook is not able to get the WebView2Loader.dll from inside the runtimes folders,
it has to be in the output directory itself.
Specifying the Platform target (to x86) was not enough, the dll was still in runtimes only.
(target framework is: .NET framework 4.7.2)
Only migrating from nuget packages.config to PackageReference (as described here: https://learn.microsoft.com/en-us/nuget/consume-packages/migrate-packages-config-to-package-reference)
and specifying the platform target
caused the dll to be copied to the output dir (bin\Debug).
We will have to prepare two separate ClickOnce installers, one for x86 and one for x64,
but now the dll is found by Outlook and WebView2 displays web pages inside FormRegion.
Update: Actually that wasn't enough for adding the WebView2Loader.dll to ClickOnce application_files too.
For that I had to define the dll as content in the csproj file:
In Visual Studio (2022) "Unload Project", then "Edit Project File" to get the .csproj of the add-in as xml, and adding the following:
<ItemGroup>
<Content Include="$(MSBuildThisFileDirectory)bin\$(Configuration)\runtimes\win-$(EffectivePlatform)\native\WebView2Loader.dll">
<Link>%(Filename)%(Extension)</Link>
<PublishState>Included</PublishState>
<Visible>False</Visible>
<CopyToOutputDirectory>Always</CopyToOutputDirectory>
<Pack>false</Pack>
</Content>
</ItemGroup>
After reloading and publishing the Loader dll was in the ClickOnce installer application files and the add-in could be distributed.