在TEdit中显示水印提示

unit  MyEdit;

interface

uses  Messages, Classes, StdCtrls, Controls, Graphics;

type
  TMyEdit  =   class (TEdit)
   private
    FCanvas: TControlCanvas;
    FWatermarkHint:  string ;
   protected
     procedure  WMPaint( var  Message: TWMPaint);  message  WM_PAINT;
     procedure  CMExit( var  Message: TCMExit);  message  CM_EXIT;
   public
     constructor  Create(AOwner: TComponent);  override ;
     destructor  Destroy;  override ;
   published
     property  WatermarkHint:  string   read  FWatermarkHint  write  FWatermarkHint;
   end ;

implementation

{  TMyEdit  }

procedure  TMyEdit.CMExit( var  Message: TCMExit);
begin
   inherited ;
  Perform(WM_PAINT,  0 ,  0 );
end ;

constructor  TMyEdit.Create(AOwner: TComponent);
begin
   inherited  Create(AOwner);
  FCanvas : =  TControlCanvas.Create;
  FCanvas.Control : =  Self;
end ;

destructor  TMyEdit.Destroy;
begin
  FCanvas.Free;
   inherited ;
end ;

procedure  TMyEdit.WMPaint( var  Message: TWMPaint);
begin
   inherited ;
   if  ( not  Focused)  and  (Self.Text  =   '' )  and  (FWatermarkHint  <>   '' )  then
   begin
    FCanvas.Font : =  Self.Font;
    FCanvas.Font.Color : =  clGrayText;
    FCanvas.TextRect(Self.ClientRect,  1 ,  1 , FWatermarkHint);
   end ;
end ;

end .