'Forms' does not exist in the namespace system.windows

Question

I have just started working on c#, and was fiddling with some code sample that I got from some forum.

This code is using a namespace using system.windows.forms for which I am getting an error:

Forms does not exist in the namespace system.windows.

Also I am getting some error related to undefined functions for senddown & sendup which I believe to be in the Forms name space.

I am using visual studio 10 (with .net frame work 4.0). Any idea how to fix this error?

Answer 1

Expand the project in Solution Tree, Right-Click on References, Add Reference, Select System.Windows.Forms on Framework tab.

You need to add reference to some non-default assemblies sometimes.

From comments: for people looking for VS 2019+: Now adding project references is Right-Click on Dependencies in Solution Explorer.

For people looking for VS Code: How do I add assembly references in Visual Studio Code

Answer 2

In case someone runs into this error when trying to reference Windows Forms components in a .NET Core 3+ WPF app (which is actually not uncommon), the solution is to go into the .csproj file (double click it in VS2019) and add it to the property group node containing the target frameworks. Like this:

<PropertyGroup>     <TargetFramework>netcoreapp3.0</TargetFramework>     <UseWPF>true</UseWPF>     <UseWindowsForms>true</UseWindowsForms> </PropertyGroup>