I read about ToolboxBitmapAttribute and while doing my usual work have decided to use it.

First of all I created my UserControl named BufferedControl which should provide double buffering functionality for me. Once I finished with my control I navigated to Toolbox to add new tool like on the picture:

And do you know what happend next? It said to me that there is no controls which could be added to the Toolbox. But why? It is derived from UserControl and looks fine. So in order to see what is the difference I added empty UserControl1 and was able to add it to the Toolbox. I thought that the reason is because I do not have designer file for my control and some specific methods like Initialize(), but after I added them nothing helped. I did more research and finally figured out that I did not have default public constructor. My constructor was like here:

BufferedControl(IBufferedControlController controller)
            Controller = controller;
            BufferContext = new BufferedGraphicsContext();
SetStyle(ControlStyles.OptimizedDoubleBuffer, false);

So lets move to adding icon of your UserControl to the Toolbox

1) First add your control and draw the icon. Below is screenshot of what I have for this.

a) Once you done, you should ensure that your control has public default constructor and that OnPaint method will not raise exceptions after it was called on instance created with default constructor.
b) Also go to properties of your icon and set Build Action –> Embedded Resource.

2) Add ToolboxBitmap attribute to your control class declaration. In my case it looks like below:

    public class BufferedControl : UserControl

3) Navigate to ToolBox and add your control from your assembly:

That’s it!