How to get TextWidth of string (without Canvas)?

I would like to get text width of a string before an application starts. Everything works fine until Application.MainForm canvas present. The problem is, when I try dynamically create TOrdinarium in the OnCreate event of the app. main form, "Canvas 开发者_StackOverflow中文版does not allow drawing" error occurs. (Application.MainForm is nil....). I tried several ways to create Canvas dynamically (one of them is written below), but it can not measure text sizes without being attached to parented control.

Is there way how to make it work somehow?

Thanx

I tried this:

  TOrdinarium = class (TCustomControl)
    private 
       function GetVirtualWidth:integer;
    end;

constructor TOrdinarium.Create(AOwner:TComponent);
begin
 inherited;
 Width:=GetVirtualWidth;
end; 

function TOrdinarium.GetVirtualWidth:integer;
var  ACanvas : TControlCanvas;
  begin
  ACanvas := TControlCanvas.Create;
  TControlCanvas(ACanvas).Control := Application.MainForm; 
  ACanvas.Font.Assign(Font);

  result:=ACanvas.TextWidth('0');

  ACanvas.Free;
  end;

This works:

procedure TForm1.FormCreate(Sender: TObject);
var
  c: TBitmap;
begin
  c := TBitmap.Create;
  try
    c.Canvas.Font.Assign(self.Font);
    Caption := IntToStr(c.Canvas.TextWidth('My String'));
  finally
    c.Free;
  end;
end;

I'm not sure if this can be done, but if by "before the app starts" you mean "before the main form is displayed", you could always put your canvas-related code in the main form's OnCreate event. You'll have a valid canvas by that point.