ImplicitUsings adds usings for both WPF and WinForms if UseWindowsForms is enabled in a WPF project

[ivansupport]

Problem

The ImplicitUsings property (enabled by default) negatively affects DevExpress customers because our WPF products depend on Windows Forms assemblies. When you create a new WPF project or enable ImplicitUsings in an existing project, the following error occurs because usings for both WPF and Windows Forms are added:

error CS0104: 'Application' is an ambiguous reference between 'System.Windows.Forms.Application' and 'System.Windows.Application'

This issue affects ALL DevExpress WPF customers who either create a new WPF project for .NET or enable ImplicitUsings in an existing project. Our estimate is that more than 50% of WPF customers will be affected by this issue, so we consider it serious/urgent.

You can reproduce the issue as follows:

Approach 1

• Create a new WPF project for .NET;
• Enable UseWindowsForms:

  <Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
  <OutputType>WinExe</OutputType>
  <TargetFramework>net6.0-windows</TargetFramework>
  <Nullable>enable</Nullable>
  <ImplicitUsings>enable</ImplicitUsings>
  <UseWPF>true</UseWPF>
  <UseWindowsForms>true</UseWindowsForms>
  </PropertyGroup>
  </Project>

Approach 2

• Create a new WPF project for .NET;
• Add a reference to a package that enables both WPF and Windows Forms (see ImplicitUsingsTest.zip).

Suggestion

Check the project type in order not to add Windows Forms usings to WPF projects.

[Alexgoon]

I'm curious if there are any updates or plans regarding this issue. It's still a serious problem since it disrupts the flow for many new users creating a new WPF project and the workaround is not obvious for them.

[mr-sven]

Found the answer on StackOverflow:

  <ItemGroup>
    <Using Remove="System.Windows.Forms" />
  </ItemGroup>

[modmynitro]

It would be nice if we do not need to use workarounds. UseWpf should work out of the box. The error also occurs if UseWindowsForms is not present.

I am currently setting UseWindowsForms to false to workaround the problem.