How to Implement the OnCreate Event for a Delphi TFrame Object

TFrame is a container for components; it can be nested within forms or other frames.

A frame, like a form, is a container for other components. Frames can be nested within forms or other frames, and they can be saved on the Component palette for easy reuse.

Missing OnCreate

Once you start using frames, you'll note there's no OnCreate event you can use to initialize your frames.

In short, the reason that a frame does not have a OnCreate event is there is no good time to fire the event.

However, by overriding the Create method you can mimic the OnCreate event. After all, the OnCreate for Forms gets fired at the end of the Create constructor — so overriding Create for Frames is as having the OnCreate event.

Here's the source code of a simple frame exposing a public property and overriding the Create constructor:

 unit WebNavigatorUnit;

interface

 uses

   Windows, Messages, SysUtils, Variants, Classes,

   Graphics, Controls, Forms, Dialogs, StdCtrls;

 type

   TWebNavigatorFrame = class(TFrame)

private

     fURL: string;

procedure SetURL(const Value: string) ;

public

     constructor Create(AOwner: TComponent) ; override;

published

     property URL : string read fURL write SetURL;

end;

implementation{$R *.dfm}

 constructor TWebNavigatorFrame.Create(AOwner: TComponent) ;

begin

   inherited Create(AOwner) ;

 //"OnCreate" code

   URL := 'http://delphi.about.com';

 end;

procedure TWebNavigatorFrame.SetURL(const Value: string) ;

begin

   fURL := Value;

   urlEdit.Text := Value;

 end;

end.

The "WebNavigatorFrame" acts as a website launcher hosting an edit and a button control. Note: if you are new to frames, make sure you read the following two articles: visual component development using frames, replacing tabsheets with frames.