Article ID: 948869
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If a Windows Forms form contains a DropDownList ComboBox control and the user drops down the list and tabs away from the control.
The item the user had hovered over will be saved but the SelectedIndexChanged event does not fire.
This is a bug in the underlying comctl32.dll (v6), which handles the themed ComboBoxes. Tabbing off of an item in the DropDownList the ComboBox is supposed to cancel the selection, and it correctly fires a CBN_SELENDCANCEL notfication and not the CBN_SELENDOK notification which WinForms wraps in the SelectedIndexChanged event. The problem is that instead of reverting to the prior selection it "reverts" back to the same new selection.
This can be worked around by forcing the ComboBox closed when tabbing off, which forces the selection to be changed fully before it can be "cancelled".
public class MyComboBox : ComboBox
protected override bool ProcessDialogKey(Keys keyData)
if (keyData == Keys.Tab)
this.DroppedDown = false;
return base.ProcessDialogKey (keyData);
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