NET 8 WinForms project fails to find types (CS0246) from NuGet package despite clean install and all caches cleared.

Question

NET 8 WinForms project fails to find types (CS0246) from NuGet package despite clean install and all caches cleared.

Thomas Abell 20

I have migrated a .NET Framework 4.8 WinForms project to .NET 8. I am using Mapsui 5.0.0-rc.2. The project fails to compile with errors like CS0246: The type or namespace name 'Shapefile' could not be found, even though the package is referenced.

Symptoms:

using statements for Mapsui.Tiling.Layers and Mapsui.Nts.Providers.Shapefile are "dimmed gray" in Visual Studio, as if unused.

The compiler cannot find types from those namespaces (e.g., Shapefile, OpenStreetMap, ThemeStyle).

This occurs even in a brand new, clean project on my machine.

Troubleshooting Steps Already Taken (None have worked):

Cleaned and rebuilt the solution multiple times.

Manually deleted all bin and obj folders.

Reinstalled all NuGet packages.

Cleared all NuGet caches using dotnet nuget locals all --clear.

Completely replaced the old .csproj file with a new, clean SDK-style project file for .NET 8.

Deleted the hidden .vs solution folder.

Performed a full "Repair" of my Visual Studio installation and rebooted.

Moved <Compile Update> tags for my Forms from a .csproj.user file to the main .csproj file.

Here is my current, clean .csproj file:

<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
	<OutputType>WinExe</OutputType>
	<TargetFramework>net8.0-windows</TargetFramework>
	<UseWindowsForms>true</UseWindowsForms>
	<RootNamespace>ReverewoodRadar</RootNamespace>
	<AssemblyName>ReverewoodRadar</AssemblyName>
	<LangVersion>latest</LangVersion>
</PropertyGroup>
<ItemGroup>
	<PackageReference Include="Mapsui.WindowsForms" Version="5.0.0-rc.2" />
	<PackageReference Include="Mapsui.Nts" Version="5.0.0-rc.2" />
	<PackageReference Include="Mapsui.Tiling" Version="5.0.0-rc.2" />
	<PackageReference Include="Mapsui.Rendering.Skia" Version="5.0.0-rc.2" />
	<PackageReference Include="NetTopologySuite.IO.Esri.Shapefile" Version="1.2.0" />
	<PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
	<PackageReference Include="SharpZipLib" Version="1.4.2" />
</ItemGroup>
<ItemGroup>
	<PackageReference Include="Microsoft.Windows.Compatibility" Version="8.0.7" />
</ItemGroup>
<ItemGroup>
	<ProjectReference Include="..\SharedLibrary\SharedLibrary.csproj" />
</ItemGroup>
<ItemGroup>
	<Compile Remove="Level3Parser.cs" />
	<Compile Remove="Level3Radar.cs" />
	<Compile Remove="Radars.cs" />
	<Compile Remove="USGSMapProvider.cs" />
</ItemGroup>
<ItemGroup>
	<None Remove="MainForm.cs.backup" />
</ItemGroup>
<ItemGroup>
	<None Update="ShapeFiles\cb_2023_us_county_500k.*">
		<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	</None>
	<None Update="ShapeFiles\cb_2023_us_state_500k.*">
		<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	</None>
	<None Update="ShapeFiles\cities.dat">
		<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	</None>
	<None Update="ShapeFiles\tl_2024_us_primaryroads.*">
		<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	</None>
</ItemGroup>
<ItemGroup>
	<Compile Update="Properties\Settings.Designer.cs">
		<DesignTimeSharedInput>True</DesignTimeSharedInput>
		<AutoGen>True</AutoGen>
		<DependentUpon>Settings.settings</DependentUpon>
	</Compile>
	<None Update="Properties\Settings.settings">
		<Generator>SettingsSingleFileGenerator</Generator>
		<LastGenOutput>Settings.Designer.cs</LastGenOutput>
	</None>
	<EmbeddedResource Update="Properties\Resources.resx">
		<Generator>ResXFileCodeGenerator</Generator>
		<LastGenOutput>Resources.Designer.cs</LastGenOutput>
	</EmbeddedResource>
</ItemGroup>
<ItemGroup>
	<Compile Update="BufferedPanel.cs">
		<SubType>Component</SubType>
	</Compile>
	<Compile Update="Form1.cs">
		<SubType>Form</SubType>
	</Compile>
	<Compile Update="MainForm.cs">
		<SubType>Form</SubType>
	</Compile>
	<Compile Update="Options.cs">
		<SubType>Form</SubType>
	</Compile>
	<Compile Update="PublishingDialog.cs">
		<SubType>Form</SubType>
	</Compile>
	<Compile Update="SettingsForm.cs">
		<SubType>Form</SubType>
	</Compile>
	<Compile Update="WarningsWindow.cs">
		<SubType>Form</SubType>
	</Compile>
</ItemGroup>
</Project>

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Answer 1

Danny Nguyen (WICLOUD CORPORATION) 3,500 Microsoft External Staff

Hi @Thomas Abell ,

Thank you for posting in this forum.

I have taken a look through your question, and I think that The CS0246 errors you’re seeing are not caused by broken NuGet references, but rather by calling the ShapeFile class wrongly.

The shapefile provider class is now named ShapeFile (with a capital F) under the Mapsui.Nts.Providers.Shapefile namespace. Older examples or blog posts may still reference Shapefile, which will no longer resolve. Other helpers, like OpenStreetMap and ThemeStyle, were removed or replaced. For example, OSM layers are now created using BruTile’s KnownTileSources, and style/theme selectors have been updated.

This is why the using statements appear gray in Visual Studio as there are no valid symbols from those namespaces being referenced.

So to fix this:

Update your code to use the new class names and APIs, e.g., Shapefile → ShapeFile.
Adjust other outdated identifiers according to Mapsui 5’s API.

Once these updates are made, your project should compile successfully. You can confirm that the NuGet packages are correctly referenced by checking that the Mapsui DLLs appear in your build output.I hope this helps. Please let me know if my solution works out for you and consider interact with the system accordingly if so.

Thomas Abell 20

I'm not an expert by any means so please bear with me. I've made the change to ShapeFiles and that helped clear some compiler errors but I'm stuck in method below.

I am trying to show or hide a LabelStyle for features in a MemoryLayer based on a function (Func<IFeature, bool> filter).

I have tried the following approaches, and all of them fail with compiler errors:

layer.Style = new ThemeStyle(f => filter(f) ? myStyle : null); (Fails with CS1729: no constructor takes 1 argument)

layer.Style = new ThemeStyle(myStyle, f => filter(f)); (Fails with CS1729: no constructor takes 2 arguments)

myStyle.Enabled = f => filter(f); (Fails with CS1660: Cannot convert lambda to bool)

layer.Style = (feature, level) => { ... } (Fails with CS1660: Cannot convert lambda to IStyle)

What is the correct C# syntax in version 5.0.0-rc.2 to apply a style to only a subset of features in a layer based on a function?

private void UpdateCityVisibility()

{

if (!(_citiesLayer is MemoryLayer citiesLayer)) return;

citiesLayer.Enabled = chkCities.Checked;

if (!citiesLayer.Enabled)

{

    mapControl.Map.Refresh();

    return;

}

var zoom = GetCurrentZoomLevel();

Func<IFeature, bool> filter = f => false;

switch (zoom)

{

    case 5: filter = f => Convert.ToInt64(f["Population"]) > 1000000; break;

    case 6: filter = f => Convert.ToInt64(f["Population"]) > 500000; break;

    case 7: filter = f => Convert.ToInt64(f["Population"]) > 75000; break;

    case 8: filter = f => Convert.ToInt64(f["Population"]) > 30000; break;

    case 9: filter = f => Convert.ToInt64(f["Population"]) > 20000; break;

    case 10: filter = f => Convert.ToInt64(f["Population"]) > 15000; break;

    case 11: filter = f => Convert.ToInt64(f["Population"]) > 10000; break;

    default:

        if (zoom >= 12) filter = f => true;

        break;

}

// 1. Define the style for visible labels.

var labelStyle = new LabelStyle

{

    ForeColor = Color.White,

    BackColor = new Brush(Color.Black),

    Halo = new Pen(Color.Black, 2),

    LabelColumn = "Name",

    CollisionDetection = true

};

citiesLayer.Style = new ThemeStyle(f => filter(f) ? labelStyle : null);

mapControl.Map.RefreshData();

mapControl.Refresh();

}

Danny Nguyen (WICLOUD CORPORATION) 3,500 Reputation points Microsoft External Staff

2025-10-08T11:16:58.44+00:00

Hi, thanks for the response.

You can create a conditional style using the ThemeStyle(Func<IFeature, IStyle?>) constructor — that’s the supported pattern in Mapsui 5.

I suggest going through the official docs for the current API and examples: Mapsui.Styles.Thematics.ThemeStyle.

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NET 8 WinForms project fails to find types (CS0246) from NuGet package despite clean install and all caches cleared.

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