Solved

Override method of component in a component.

Posted on 2006-06-19
3
288 Views
Last Modified: 2010-04-05
Ive got this component that im making, which is basically just a regular label, except when you double-click it, it turns into an edit box so that you can edit the caption of the label.  Anyways, my component descends from the TCustomLabel, and on the double click, it creates an Edit box, as so:

procedure TEditorLabel.DblClick;
begin
  // FEdit := TEdit.Create(Self.Owner);                                   <-- This is what is created in the constructor of the component....
  Self.Visible := False;
  FEdit.Left := Self.Left; FEdit.Top := Self.Top;
  FEdit.Text := Self.Caption;
  FEdit.Parent := Self.Parent;
end;

This works great, except that I want to override the OnKeyDown event of this new edit!  So I want to do

FEdit.OnKeyDown := ___________;

except, how would I do that?  It seems that I cant just create an event and assign it.... so what do I do?
0
Comment
Question by:cholin
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
3 Comments
 
LVL 26

Accepted Solution

by:
Russell Libby earned 125 total points
ID: 16939159
Yes, you can just assign an event at runtime.... just add it as a public/protected method of your class and make sure it matches the event type for OnKeyDown, eg:

type
  TEditorLabel      =  class(TLabel)
  private
     // Private declarations
     FEdit:         TEdit;
  protected
     // Protected declarations
     procedure      DblClick; override;
     procedure      OnKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  public
     // Public declarations
     constructor    Create(AOwner: TComponent); override;
  end;

--

constructor TEditorLabel.Create(AOwner: TComponent);
begin

  // Perform inherited
  inherited Create(AOwner);

  // Create edit
  FEdit:=TEdit.Create(Self);

  // Your code....

end;

procedure TEditorLabel.OnKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin

  //
  // Do whatever is required ...
  //

end;

procedure TEditorLabel.DblClick;
begin

  Self.Visible := False;
  FEdit.Left := Self.Left; FEdit.Top := Self.Top;
  FEdit.Text := Self.Caption;
  FEdit.Parent := Self.Parent;
  FEdit.OnKeyDown := Self.OnKeyDown;

end;


--

Regards,
Russell

0
 
LVL 1

Author Comment

by:cholin
ID: 16939335
Alright, it works now for the most part, except that when I close my program, it gives me access errors which means that Im not cleaning up properly....  any idea what's wrong with this code?

constructor TEditorLabel.Create(AOwner: TComponent);
begin
  inherited;
  FEdit := TEdit.Create(Self);
end;

destructor TEditorLabel.Destroy;
begin
  FEdit.OnKeyPress := nil;
  FEdit.Free;
  inherited;
end;

procedure TEditorLabel.DblClick;
begin
  Visible := False;
  FEdit.Left := Left - 2; FEdit.Top := Top - 2;
  FEdit.Text := Caption;
  FEdit.Parent := Parent;
  FEdit.OnKeyPress := OnKeyPress;
end;

procedure TEditorLabel.OnKeyPress(Sender: TObject; var Key: Char);
begin
  if Key = #13 then begin
    Key := #0;
    Caption := FEdit.Text;
    FEdit.Visible := False;
    Visible := True;
  end;
end;

If I just open and close the application, it works just fine, meaning that the FEdit is getting created and destroyed just fine... so now why does it throw exceptions when I close the application after executing the DblClick event?  
0
 
LVL 1

Author Comment

by:cholin
ID: 16939347
Nevermind, turns out you can't call FREE if you pass a valid owner in the constructor (http://delphi.about.com/od/kbcurt/a/dynamiccreation.htm)
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

A lot of questions regard threads in Delphi.   One of the more specific questions is how to show progress of the thread.   Updating a progressbar from inside a thread is a mistake. A solution to this would be to send a synchronized message to the…
This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
Finds all prime numbers in a range requested and places them in a public primes() array. I've demostrated a template size of 30 (2 * 3 * 5) but larger templates can be built such 210  (2 * 3 * 5 * 7) or 2310  (2 * 3 * 5 * 7 * 11). The larger templa…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question