Problem with Combobox PreviewKeyDown Enent

Question

Hi.
Follow this Steps:
create new application in c#.net
place 1 combobox and 1 textbox on form
on PreviewKeyDown Event for combobox write a code also for text box
now run the application and set focus to combobox and press any key!
the code you typed run 2 times!! but for textbox run only 1 times!
very thanx
exeuse me for bad english!