How do I get the Control that is under the cursor in Delphi?

Question

I need the opposite information that the question "How to get cursor position on a control?" asks.

Given the current cursor position, how can I find the form (in my application) and the control that the cursor is currently over? I need the handle to it so that I can use Windows.SetFocus(Handle).

For reference, I'm using Delphi 2009.

Answer 1

I experienced some problems with suggested solutions (Delphi XE6/Windows 8.1/x64):

• FindVCLWindow doesn't search disabled controls (Enabled=False).
• TWinControl.ControlAtPos doesn't search controls if they are disabled indirectly (for example if Button.Enabled=True, but Button.Parent.Enabled=False).

In my case it was a problem, because i need to find any visible control under the mouse cursor, so i have to use my own implementation of function FindControlAtPos:

function FindSubcontrolAtPos(AControl: TControl; AScreenPos, AClientPos: TPoint): TControl;
var
  i: Integer;
  C: TControl;
begin
  Result := nil;
  C := AControl;
  if (C=nil) or not C.Visible or not TRect.Create(C.Left, C.Top, C.Left+C.Width, C.Top+C.Height).Contains(AClientPos) then
    Exit;
  Result := AControl;
  if AControl is TWinControl then
    for i := 0 to TWinControl(AControl).ControlCount-1 do
    begin
      C := FindSubcontrolAtPos(TWinControl(AControl).Controls[i], AScreenPos, AControl.ScreenToClient(AScreenPos));
      if C<>nil then
        Result := C;
    end;
end;

function FindControlAtPos(AScreenPos: TPoint): TControl;
var
  i: Integer;
  f,m: TForm;
  p: TPoint;
  r: TRect;
begin
  Result := nil;
  for i := Screen.FormCount-1 downto 0 do
    begin
      f := Screen.Forms[i];
      if f.Visible and (f.Parent=nil) and (f.FormStyle<>fsMDIChild) and 
        TRect.Create(f.Left, f.Top, f.Left+f.Width, f.Top+f.Height).Contains(AScreenPos) 
      then
        Result := f; 
    end;
  Result := FindSubcontrolAtPos(Result, AScreenPos, AScreenPos);
  if (Result is TForm) and (TForm(Result).ClientHandle<>0) then
  begin
    WinAPI.Windows.GetWindowRect(TForm(Result).ClientHandle, r);
    p := TPoint.Create(AScreenPos.X-r.Left, AScreenPos.Y-r.Top);
    m := nil;
    for i := TForm(Result).MDIChildCount-1 downto 0 do
    begin
      f := TForm(Result).MDIChildren[i];
      if TRect.Create(f.Left, f.Top, f.Left+f.Width, f.Top+f.Height).Contains(p) then
        m := f; 
    end;
    if m<>nil then
      Result := FindSubcontrolAtPos(m, AScreenPos, p);
  end;
end;