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I'm having difficulty getting Delphi 2006 to assign event handlers to a component on a TFrame that are independent.

Say I have a frame TComboFrame that contains a TCombo Combo1 and I use this in several places on my main form.

When I place an instance of TComboFrame MyFrame1 onto my main form, and I want to assign an event handler to the combo, I do it by clicking on the TCombo inside the frame MyFrame1 that I have placed on the form, and double clicking in the empty OnChange field in the object inspector Events tab.

Normally the creates a new handler with a name like:

procedure TMainForm.MyFrame1Combo1Change(Sender: TObject);

and the event handler name is derived from both the name of the component on the ancestor TComboFrame (Combo1) and the name of the instance I have placed on my form (MyFrame1) - i.e. unique to that instance of the TComboFrame. I can then do this for other instances of the frame that I have placed on my main form and they each get their own event handlers.

If I wanted an event handler that fired for all instances of the frame, I would open the ancestor frame itself and do it there.

This is my understanding of how it is supposed to work, but something has gone wrong somewhere. Of the several instances of the frame on my main form, some have their own event handlers, and some have a common event handler,

procedure TDMainForm.ComboFrame1Combo1Change(Sender: TObject);

Nothing I have tried has broken this phantom link Delphi seems to have with this common event handler that is shared by several of the frames.

How can I repair this state, and what causes it in the first place?

** UPDATE 1 **

I have found after reading the responses and a bit of experimenting that I can repair the offending components by the following procedure:

1) remove all event handlers for the frame.
2) delete the frame, remembering it's name.
3) copy another one that is known to be OK (i.e. has it's own event names that are "individual").
4) paste that one in place of the one you deleted.
5) Restore the original name.
6) Create your event handlers.

...at least, it worked for me at least once...

** UPDATE 2 **

Another way to cure it seems to be to overtype the event handler name that it creates when you double-click in the empty event field in Object Inspector, with a new unique name, and then double-click on the name again. Delphi then creates an empty handler with the unique name.

rossmcm
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3 Answers3

3

I would write another event in the frame and set it when I want another OnChange event, like this:

type
  TFrame2 = class(TFrame)
    ComboBox1: TComboBox;
    procedure ComboBox1Change(Sender: TObject);
  private
    FMyChangeEvent: TNotifyEvent;
  public
    property MyChangeEvent: TNotifyEvent read FMyChangeEvent write FMyChangeEvent
  end;

implementation

{$R *.dfm}

procedure TFrame2.ComboBox1Change(Sender: TObject);
begin
  //Your default combo behavior here
  if Assigned(FMyChangeEvent) then
    FMyChangeEvent(Self);
end;

And where I need to add something to the OnChange behavior:

type
  TForm1 = class(TForm)
    MyLittleFrame: TFrame2;
  private
    procedure MyOwnCustomLittleOnChangeBehavior(Sender: TObject);
  public
    constructor Create(AOwner: TComponent); override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

constructor TForm1.Create(AOwner: TComponent);
begin
  inherited;
  MyLittleFrame.MyChangeEvent :=  MyOwnCustomLittleOnChangeBehavior;
end;

procedure TForm1.MyOwnCustomLittleOnChangeBehavior(Sender: TObject);
begin
  ShowMessage('42');
end;

I usually do this because I don't trust the delphi way of setting events in the DFM, its very easy to just remove the whole event without noticing.

Fabio Gomes
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1

Simply single-click on a TCombo that you want to break the link to, clear its OnClick event handler assignment in the Object Inspector, and then double-click on the event to generate a new event handler. Of course, if the generated event handler name already exists, it will be re-used, but at least the Object Inspector will re-evaluate all of the object names when generating the event.

Of course, this is not a very object-oriented approach. What Fabio suggests is a better choice. Though I would suggest declaring the TFrame event as published instead of public so you can assign it at design-time like any other event.

Remy Lebeau
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  • I don't like published events either, if you ever need to remove them, you will get errors just in runtime. So if possible I like to avoid declaring published events. It is good just if its an end user component which you are going to share and would like them to set the events in the object inspector. – Fabio Gomes Apr 06 '12 at 01:26
  • Thanks @Remy. Still no dice. I still get a handler with a name based on the ancestor name and not the individual component, and that then happens for all other events of that frame, and all other instances of the frame that are "damaged". The event hander name does not already exist anywhere in my source. See addendum to OP for more. – rossmcm Apr 06 '12 at 03:08
1

I can't recreate this behaviour in Delphi6 or Delphi 2009. It seems to me with lots of frames (and changing their names adding and deleting maybe) you have fooled/befuddled Delphi's naming convention which it uses by default to link the events and frames have ended up with the same names as previous ones.

Therefore double clicking the event handlers just puts you at an event handler with the same name as one that was created by a previously deleted (or renamed) frame (but deleting the frame does not delete the old event handlers. IYSWIM :)

Therefore my answer is you've got fuddled by getting the frames names & event handler names in a muddle!

Despatcher
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