System.Resources.MissingManifestResourceException when DependentUpon not specified and .resx path not match with Control/Form namespace

Visual Studio Version: 16.3.0

Summary: .Net Core 3.0 Microsoft.NET.Sdk.WindowsDesktop UseWindowsForms = true System.Resources.MissingManifestResourceException when DependentUpon not specified and .resx path not match with Control/Form namespace.

Steps to Reproduce:

1. Create new WindowsForms project (sdk style, net472).
2. Add local resource to Form1 (e.g. BackgroundImage).
3. Change Form1 namespace or move it to another folder in project.
4. Build and run application.

Expected Behavior: Application starts and Form1 shown with set background image.

Actual Behavior: System.Resources.MissingManifestResourceException thrown when this.BackgroundImage = (System.Drawing.Image)resources.GetObject("$this.BackgroundImage"))) called.

Content of csproj file:

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net472</TargetFramework>
    <UseWindowsForms>True</UseWindowsForms>
  </PropertyGroup>

</Project>

Workaround: Add next item in csproj file:

  <ItemGroup>
    <!-- "NewFolder" is project subfolder where form has been moved. -->
    <EmbeddedResource Update="NewFolder/Form1.resx" DependentUpon="Form1.cs" />
  </ItemGroup>

[AdamDotNet]

I’ve been researching this too, lately. Try adding this property to your CSProj.

<PropertyGroup>
 <EmbeddedResourceUseDependentUponConvention>true</EmbeddedResourceUseDependentUponConvention>
</PropertyGroup>

Which I found via: /dotnet/sdk/pull/3533

Remove your workaround <EmbeddedResource Update="..." after adding the above property and you should be good to go.

Note that this flag is set to true for .Net Core 3.0+ and .Net Standard 2.1+, but needs to be opted in like this for other TFMs. This flag has worked for me on my projects using Sdk="Microsoft.NET.Sdk.WindowsDesktop" WinForms projects targeting net48 where the namespace of the form did not match the folder it was in.

[ds1709]

Yes, it works now. Thanks.