What are my options for filtering custom .net controls from the WinForms toolbox of Visual Studio 2008?

Question

Visual Studio 2008 does a much better job of detecting and adding controls from projects to the toolbox for use in the forms designer. If you have an assembly with a UserControl- or DataSet-derived type, then it will automatically detect and add that control to the toolbox for designing forms. This is slightly better than the old system in 2005 that made you manually add controls and would occasionally forget them, etc.

However, on the legacy, monolithic project I am working on (now upgraded to vs2008) this means many controls that I don't want and don't need (and a redesign would not be warranted against so much legacy code :( ). I imagine that if I made certain types internal or private, then they wouldn't show up. However, I need many of those to remain public, but not show up in the toolbox. Furthermore, with so many controls getting added to the toolbox, opening the winforms designer slows significantly.

1. Is there an attribute or other mechanism that prevents toolbox appearance (that wouldn't otherwise affect functionality) ?
2. Would filtering using such a mechanism improve performance while still autodetecting new types that SHOULD be in the toolbox? (I know you can disable the autodetect, but its nice to have in many cases)
3. Have others encountered this irritation on large solutions (with many csproj/vbproj files)?

Edit: Thanks everyone! I knew it had to be simple (and was likely an attribute) but that fills the gap. Nice to know that I was in good company in not knowing about ToolBoxItem(false).

Answer 1

Go through the toolbox and for each custom control that you see that you want to hide, add the following attribute above the class:

[ToolboxItem(false)]

Of course, this is a compiled attribute and will affect everyone using the code, so I only recommend doing this for controls that don't make drag-drop sense. Otherwise, you will probably make someone that loves that control very very angry. :)

Answer 2

The following attribute should hide it from the toolbox:

[ToolboxItem(false)]

If you apply it to all the types you don't want to show, it will still show any new ones you create without this attribute. Note, you may have to manually remove the items to start with.

This blog post shows some other attributes you may want to use.