How can I get a TEdit's canvas in Delphi?

Question

I want to shorten a filename to fit in a TEdit, something like

Edit1.Text := MinimizeName(FileName, Edit1.Canvas, Edit1.Width);

Unfortunately this doesn't compile because a TEdit does have a Canvas property directly. The canvas is needed for its font metrics. How can I access a TEdit's canvas?

(MinimizeName is declared in Vcl.FileCtrl.)

Answer 1

You could use TControlCanvas. You should also take the control's Font into account.

e.g.:

var
  Canvas: TControlCanvas;

Canvas := TControlCanvas.Create;
try
  Canvas.Control := Edit1;
  Canvas.Font.Assign(Edit1.Font); 

  // Do something with Canvas... 
finally
  Canvas.Free;
end;

If you want to use this on a TWinControl variable you have to use the usual protected access trick:

type
  TWinControlAccess = class(TWinControl);

procedure Test(AWinControl: TWinControl);
var
  Canvas: TControlCanvas;
begin
  Canvas := TControlCanvas.Create;
  try
    Canvas.Control := AWinControl;
    Canvas.Font.Assign(TWinControlAccess(AWinControl).Font);

    // Do something with Canvas...
  finally
    Canvas.Free;
  end;
end;