Use Styled SysColor for selected text in TEdit

Question

I am using Delphi XE3 to build a VCL application. This VCL application is styled using the buildin stying from unit Vcl.Styles.

In the style I am using the SysColor clHighlight has been altered but when a piece of text is selected in a TEdit (or TComboBox or TMemo) the default system highlight color is used (defaults to blue) for coloring the background of the selected text.

NB: Other controls use the SysColor clHighlight for selected items from the style.

Question: how can you specify this color in the style?

Answer 1

This is a limitation of the WinApi, the highlight color used by these controls can't be modified directly. The only workaround is hook and replace the GetSysColor method by the StyleServices.GetSystemColor function. like so

implementation

uses
  DDetours,
  WinApi.Windows,
  Vcl.Styles,
  Vcl.Themes;

var
  TrampolineGetSysColor:  function (nIndex: Integer): DWORD; stdcall;
  GetSysColorOrgPointer : Pointer = nil;

function InterceptGetSysColor(nIndex: Integer): DWORD; stdcall;
begin
  if StyleServices.IsSystemStyle then
   Result:= TrampolineGetSysColor(nIndex)
  else
   Result:= StyleServices.GetSystemColor(nIndex or Integer($FF000000));
end;

initialization
 if StyleServices.Available then
 begin
    GetSysColorOrgPointer := GetProcAddress(GetModuleHandle('user32.dll'), 'GetSysColor');
    @TrampolineGetSysColor := InterceptCreate(GetSysColorOrgPointer, @InterceptGetSysColor);
 end;
finalization
  if GetSysColorOrgPointer<>nil then
    InterceptRemove(@TrampolineGetSysColor);

end. 

Before

After

Btw the VCL Styles Utils project includes a unit with this hook.