I played around with making unclickable separator items (as described in this answer) and ran into several UI glitches. The problem is that combo boxes have several aspects to their behavior that can be hard to get exactly right:
- Pressing the up and down arrow keys navigates the list while the list is dropped down.
- Pressing Enter closes the dropped down list, selecting the current item.
- Pressing Escape closes the dropped down list, selecting the current item (if the current item was chosen with the up and down arrow keys) or the last selected item.
- If the combo box has the focus, then pressing the up and down arrow keys to changes the current selection without displaying the list.
- If the combo box has the focus, then typing anything selects the combo box item matching whatever is typing.
- If the combo box has the focus, then pressing F4 drops down the combo box list, which can then be controlled by keyboard or mouse.
Ensuring that disabled separator items don't respond to any of these events (plus any other events which I may be missing, e.g., screen readers?) seems fraught with error.
Instead, the approach I'm using is to draw the separator as part of the item:
- Use a variable height owner draw combo box.
- Add 3 pixels to the height for any items that need separators.
- Draw a horizontal line at the top of each item needing a separator.
Here's some C++Builder code to accomplish this; translating it to Delphi should be easy enough.
void __fastcall TForm1::ComboBox1DrawItem(TWinControl *Control,
int Index, TRect &Rect, TOwnerDrawState State)
{
bool draw_separator = NeedsSeparator(Index) &&
!State.Contains(odComboBoxEdit);
TCanvas *canvas = dynamic_cast<TCustomCombo*>(Control)->Canvas;
canvas->FillRect(Rect);
TRect text_rect = Rect;
// Add space for separator if needed.
if (draw_separator) {
text_rect.Top += 3;
}
canvas->TextOut(text_rect.Left + 3,
(text_rect.Top + text_rect.Bottom) / 2 -
canvas->TextHeight(ComboBox1->Items->Strings[Index]) / 2),
ComboBox1->Items->Strings[Index]);
// Draw a separator line above the item if needed.
if (draw_separator) {
canvas->Pen->Color = canvas->Font->Color;
canvas->MoveTo(Rect.Left, Rect.Top + 1);
canvas->LineTo(Rect.Right, Rect.Top + 1);
}
}
void __fastcall TForm1::ComboBox1MeasureItem(
TWinControl * /* Control */, int Index, int &Height)
{
Height = ComboBox1->ItemHeight;
// Add space for the separator if needed.
if (Index != -1 && NeedsSeparator(Index)) {
Height += 3;
}
}
