BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Identifying Sender: TObject          BorlandTalk.com Forum Index -> comp.lang.pascal.delphi.misc View previous topic :: View next topic   Author Message Paul E. Schoen Guest Posted: Mon Jan 16, 2006 8:17 am    Post subject: Identifying Sender: TObject In the following code, I can set a breakpoint as noted, and it is triggered, indicating Sender = ReclData, as I expected. However, if I inspect Sender, or WhoSentIt, the result is (); How could I identify the Sender if I didn't already know all possible senders? How does the equality know? var WhoSentIt: TObject; procedure TReclData.FormClose(Sender: TObject; var Action: TCloseAction); begin If Sender = ReclData then WhoSentIt := Sender; // Set Breakpoint Here Action := caFree; end; This is just a matter of curiosity for now. I appreciate all help provided on other more critical matters, and I'm sure I will have more as I try to clean up several thousand lines of code -- Paul E. Schoen, President P S Technology, Inc. Cockeysville, MD www.pstech-inc.com Back to top Nicholas Sherlock Guest Posted: Mon Jan 16, 2006 8:43 am    Post subject: Re: Identifying Sender: TObject Paul E. Schoen wrote: Quote: If I inspect Sender, or WhoSentIt, the result is (); This is simply because the IDE has no useful information to show you. Quote: How could I identify the Sender if I didn't already know all possible senders? How does the equality know? It checks to see if both pointers point to the same object. Your question is odd, what exactly are you trying to achieve? Cheers, Nicholas Sherlock Back to top Tom de Neef Guest Posted: Mon Jan 16, 2006 9:08 am    Post subject: Re: Identifying Sender: TObject "Paul E. Schoen" <pstech (AT) smart (DOT) net> schreef in bericht news:11smlh4mdvv8741 (AT) corp (DOT) supernews.com... Quote: In the following code, I can set a breakpoint as noted, and it is triggered, indicating Sender = ReclData, as I expected. However, if I inspect Sender, or WhoSentIt, the result is (); How could I identify the Sender if I didn't already know all possible senders? How does the equality know? var WhoSentIt: TObject; procedure TReclData.FormClose(Sender: TObject; var Action: TCloseAction); begin If Sender = ReclData then WhoSentIt := Sender; // Set Breakpoint Here Action := caFree; end; You can try evaluating Sender.classname or sender.classtype. Once you know the class (eg Tedit), you can see more by typecasting sender, eg Tedit(sender).name. Tom Back to top Maarten Wiltink Guest Posted: Mon Jan 16, 2006 9:31 am    Post subject: Re: Identifying Sender: TObject "Paul E. Schoen" <pstech (AT) smart (DOT) net> wrote Quote: In the following code, I can set a breakpoint as noted, and it is triggered, indicating Sender = ReclData, as I expected. However, if I inspect Sender, or WhoSentIt, the result is (); How could I identify the Sender if I didn't already know all possible senders? How does the equality know? The equality is a simple pointer comparison. Sender and WhoSentIt are of compatible types, so they can be compared. If Sender were a TGraphicControl and WhoSentIt a TWinControl, you'd know in advance they'd never be the same (unless both nil). Note carefully what the debugger knows. Sender and WhoSentIt are both TObjects. They _may_ be instances of derived classes, but not necessarily. All the debugger knows for sure is TObject. TObject has no fields, which is what it shows. Add a watch for TComponent(Sender) and you'll see fields. Assuming Sender really is a TComponent. (The watch window does not support "as" casting.) As to _identifying_ the Sender, it's often not necessary. You should be interested in its behaviour, not its identity. Say for the sake of example that you have an event handler that disables the control that fired the event. The Sender is declared TObject; it must be, there are actually good reasons for that. You _check_ that Sender is a TControl, cast it, and set its Enabled to False. Enabled is introduced in TControl, so you need TControl, but you _don't_ need to know exactly _which_ editbox or button you're talking to. Polymorphism in action. There are cases where you really want to know which of a few possible senders called an event handler, but they are IME rare. Groetjes, Maarten Wiltink Back to top Paul E. Schoen Guest Posted: Mon Jan 16, 2006 9:58 am    Post subject: Re: Identifying Sender: TObject "Tom de Neef" <tdeneef (AT) qolor (DOT) nl> wrote Quote: "Paul E. Schoen" <pstech (AT) smart (DOT) net> schreef in bericht news:11smlh4mdvv8741 (AT) corp (DOT) supernews.com... In the following code, I can set a breakpoint as noted, and it is triggered, indicating Sender = ReclData, as I expected. However, if I inspect Sender, or WhoSentIt, the result is (); How could I identify the Sender if I didn't already know all possible senders? How does the equality know? var WhoSentIt: TObject; procedure TReclData.FormClose(Sender: TObject; var Action: TCloseAction); begin If Sender = ReclData then WhoSentIt := Sender; // Set Breakpoint Here Action := caFree; end; You can try evaluating Sender.classname or sender.classtype. Once you know the class (eg Tedit), you can see more by typecasting sender, eg Tedit(sender).name. Tom I used TReclData as a typecast, and it works perfectly. When I clicked a button, it gave me the name of the button in its OnClick handler. When it came from the OnClose event handler above, it gave me the form 'ReclData'. It may come in handy at some time, probably for debugging. Thank You! :) Paul Back to top Sonnich Guest Posted: Tue Jan 17, 2006 6:12 pm    Post subject: Re: Identifying Sender: TObject Not that it matters, but this is somehow useful, e.g. when using the OnMouseMove. To give you some ideas, this is what I have been diong during times: if Sender is TButton then... if TButton(Sender) = btnClickMe then .... if sender = nil then... and things like that. 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