< Continued from page 2

The following example shows how to complete partial strings typed into a combo box. The code represents the OnKeyPress event handler of the combo box, which performs most of the default keystroke handling before finding matching list item and updating the text.

Note: This OnKeyPress event handler does not deal with the case when the user types the Delete key. That case must be caught in the OnKeyDown event handler instead.

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procedure TForm1.ComboBox1KeyPress(Sender: TObject; var Key: Char) ;
var
   Found: boolean;
   j,SelSt: Integer;
   TmpStr: string;
begin
   { first, process the keystroke to obtain the current string }
   { This code requires all items in list to be uppercase}
   if Key in ['a'..'z'] then Dec(Key,32) ; {Force Uppercase only!}
   with (Sender as TComboBox) do
   begin
     SelSt := SelStart;
     if (Key = Chr(vk_Back)) and (SelLength <> 0) then
      TmpStr := Copy(Text,1,SelStart)+Copy(Text,SelLength+SelStart+1,255)

     else if Key = Chr(vk_Back) then {SelLength = 0}
      TmpStr := Copy(Text,1,SelStart-1)+Copy(Text,SelStart+1,255)
     else {Key in ['A'..'Z', etc]}
      TmpStr := Copy(Text,1,SelStart)+Key+Copy(Text,SelLength+SelStart+1,255) ;
     if TmpStr = '' then Exit;
     { update SelSt to the current insertion point }

     if (Key = Chr(vk_Back)) and (SelSt > 0) then Dec(SelSt)

     else if Key <> Chr(vk_Back) then Inc(SelSt) ;
     Key := #0; { indicate that key was handled }
     if SelSt = 0 then
     begin
       Text:= '';
       Exit;
     end;

    {Now that TmpStr is the currently typed
     string, see if we can locate a match }

     Found := False;
     for j := 1 to Items.Count do
       if Copy(Items[j-1],1,Length(TmpStr)) = TmpStr then
       begin
         Text := Items[j-1]; { update to the match that was found }
         ItemIndex := j-1;
         Found := True;
         Break;
       end;
     if Found then { select the untyped end of the string }
     begin
       SelStart := SelSt;
       SelLength := Length(Text)-SelSt;
     end
     else Beep;
   end;
end;
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