Compiler cannot find System.Windows.Forms namespace

Question

I'm writing a console app in C#, targeting .Net 8.0. I want to pop a MessageBox, but the compiler can't find System.Windows.Forms. Here's a screenshot of the error:

I've searched but cannot find an assembly or package that fixes this issue. Any ideas?

Answer 1

Try to double-click the project in Solution Explorer, and enter the <UseWindowsForms> element:

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

    <PropertyGroup>
        . . .
        <UseWindowsForms>true</UseWindowsForms>
    </PropertyGroup>
   . . .

Save it. Then right-click the project, go to Property, and select “Windows” in Target OS field.

Answer 2

You can create a Windows Forms project, under project properties change Output type to Console Application. Then in Program.cs

namespace WinFormsApp2;

internal static class Program
{
    /// <summary>
    ///  The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        MessageBox.Show("Test");
    }
}

Or

namespace WinFormsApp2;

internal static class Program
{
    /// <summary>
    ///  The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        ApplicationConfiguration.Initialize();
        MessageBox.Show("Test");
    }
}