TCustomComboBox: Support Windows Message CB_SETDROPPEDWIDTH

Original Reporter info from Mantis: Simon Ameis @SAmeis

• Reporter name: Simon Ameis

Description:

Currently the property TCustomComboBox.ItemWidth is ignored on Windows. This may be changed by sending a CB_SETDROPPEDWIDTH message to the combobox's handle.

https://msdn.microsoft.com/en-us/library/windows/desktop/bb775901%28v=vs.85%29.aspx

Additional information:

The correct place where to put this SendMessage could be TWin32WidgetSet.SetComboMinDropDownSize() which may be changed to 
<code>function TWin32WidgetSet.SetComboMinDropDownSize(Handle: HWND; MinItemsWidth,
  MinItemsHeight, MinItemCount: integer): boolean;
begin
  Result:= ThemeServices.ThemesEnabled and
    boolean(Windows.SendMessage(Handle, CB_SETMINVISIBLE, MinItemCount, 0));
  Result := Result and boolean(Windows.SendMessage(Handle, CB_SETDROPPEDWIDTH, MinItemsWidth, 0));
end;</code>

But this method is never called during application startup; this may be an error in TCustomComboBox.AdjustDropDown:
<code>procedure TCustomComboBox.AdjustDropDown;
var
  Count, MinItemsWidth, MinItemsHeight: Integer;
begin
  if (not HandleAllocated) or (not DroppedDown) then exit;
  Count := Items.Count;
  if Count > DropDownCount then Count := DropDownCount;
  if Count < 1 then Count := 1;
  MinItemsWidth := ItemWidth;
  MinItemsHeight := Count * ItemHeight;
  SetComboMinDropDownSize(Handle, MinItemsWidth, MinItemsHeight, Count);
end;</code>
may need to be changed to
<code>procedure TCustomComboBox.AdjustDropDown;
var
  Count, MinItemsWidth, MinItemsHeight: Integer;
begin
  if (not HandleAllocated) then exit;
  Count := Items.Count;
  if Count > DropDownCount then Count := DropDownCount;
  if Count < 1 then Count := 1;
  MinItemsWidth := ItemWidth;
  MinItemsHeight := Count * ItemHeight;
  SetComboMinDropDownSize(Handle, MinItemsWidth, MinItemsHeight, Count);
end;</code>

Mantis conversion info:

• Mantis ID: 29149
• OS: Windows
• Version: 1.4.4
• Fixed in version: 1.7 (SVN)
• Fixed in revision: 51094 (#9effa4e6)
• Target version: 1.6