Question

It’s obviously a bug, but I cannot track down why happens. Here is a minimalistic code to reproduce. Just drop a combo box and button on a form and write the following event handlers:

procedure TForm1.FormCreate(Sender: TObject);
begin
  ComboBox1.Items.Add('A Item');
  ComboBox1.Items.Add('B Item');
  ComboBox1.Items.Add('C Item');
  ComboBox1.Style := csDropDown;
  ComboBox1.AutoComplete := False;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ComboBox1.Text := 'B';
  ComboBox1.Font.Color := clRed;
  ShowMessage(IntToStr(ComboBox1.ItemIndex));
end;

When you click the button for the first time, you will see in the combo edit fully selected text of the second item, but message box will show you the item index equals to -1. When you drop down it, the second item seems to be selected. The second click will set the proper text though, but the rest will be the same as at the first click. So, combo box in this case behaves like if some weird autocompletion would be enabled.

I’ve tracked this down to the EditWndProc where after font change is received WM_SETTEXT message with the text of the second item, but I don’t know where it comes from and why with the text of the second item.

So, my question is quite specific – what (which method) sends the WM_SETTEXT at font change and how does it know about second item text match when the autocompletion is disabled ?

So far I could reproduce this in Delphi 2009 and Delphi XE3 on Windows 7 Home Premium 64-bit with the most recent updates installed.

Answer 1

I don’t think this is a VCL issue, looking at the call stack, it seems that message seems is handled through comctl32.dll.
You can solve the problem by setting the font color before setting the text:

procedure TForm1.Button1Click(Sender: TObject);
begin
  ComboBox1.Font.Color := clRed;
  ComboBox1.Text := 'B';
  ShowMessage(IntToStr(ComboBox1.ItemIndex));
end;