Abstract answer
The designer only makes sense for some types of files. For example, Windows Forms designer exists for classes that inherit System.Windows.Forms.Control
, and when the relevant attributes for that file are set in the project.
Practical answer
- Make sure you have a project that allows Forms (like "Windows Forms Application" or "Windows Forms Control Library"), create one if needed.
- In project tree, right-click on the project and use some "add new ..." in the context menu.
- There, choose "Form" or "Control" depending on your intent. It should create and configure what's needed, and you'll be able to use the designer.
In Visual Studio you can switch between text and designer with a shortcut key (F7, Shift-F7) or context menu. In sharpdevelop use the "Source" and "Design" tabs.