You can define a cell and then register it in the toolbox in a project that is currently being debugged (similar to how this is done with a user control on a form). This allows you to use the toolbox in the same way as you would when handling a user control in the Windows Form Designer.
Adding User Defined Cell in Same Project
When you add a user defined cell using source code in the same project, building the project displays the user defined cell in the designer toolbox. This does not require any extra steps.
Adding User Defined Cell Defined in External Assembly
In order to register and use a user defined cell that is built as an assembly (.exe, .dll) into the toolbox, drag and drop this file from explorer to the Visual Studio toolbox.
See Also