[Gambas-user] Events not firing in dynamically instantiated forms.

[T Lee Davidson]

Wow. That is a very good explanation. Thank you, Tobi!

I did understand that "a form is by default its own event observer". But 
I guess I did not fully understand exactly what that meant.

(And, yes, I have seen code like, "Public Sub Form_Open()", and always 
wondered why it did not say "Form1_Open()".)

I thought, when I first asked, that it would be a simple answer. (I 
apologize to you, Stephen, for unintentionally hi-jacking your thread. I 
did think you were done with it.)

Okay, so:
1. Should that warning actually say, "Unless ~Class~ is a 
[Form](/comp/gb.qt4/form), if you forget to specify the ~Name~ part, 
your object will never raise events!"

2. And, should this explanation be put on the Wiki somewhere? If so, where?


-- 
Lee
__________

"Artificial Intelligence is no match for natural stupidity."


On 11/27/2014 01:47 PM, Tobias Boege wrote:
>> Thanks Tobi. I understand that a form is by default its own event observer.
>> >
>> >What confuses me is that the warning seems to indicate that the "As
>> >Name" part is required for the object to be able to raise events.
>> >
>> >Thinking that the warning should say, "*If you specify As*  but forget to
>> >specify the Name part ...", I took off just the Name part leaving "As"
>> >at the end of the line. I then got, "Unexpected end of line".
>> >
>> >So, I guess I'm just confused as to what that warning is actually saying.
>> >
> OK, "As name" comes as a bundle. It makes your newly created object raise
> events under the given name and makes the current class its event observer.
> This is called "attaching" the object to its observer. "As" without a name
> is a syntax error.
>
> This means that in a class Bob the lines
>
>    Private h As Alice
>
>    Public Sub _new()
>      h = New Alice As "Beth"
>    End
>
> create a new Alice in the variable "h" and assigns her the event name "Beth"
> (just to show that the event name is totally free to choose).
>
> The current Bob where you create that Alice is now her event observer, that
> is you can intercept the events of "h" in the code of Bob. Say, Alice raises
> an event called "Send", you can write
>
>    Public Sub Beth_Send()
>      ' This is called when the h object raises the Send event.
>    End
>
> in your Bob.class. Take your time to experiment if you're still insecure
> here. (Or ask for a concrete example!)
>
> If you don't give "As name", the object will not be attached to any observer
> and this will prevent it from raising events (actually it_can_  raise events
> but nobody will hear it).
>
> But Form plays a special role. It will attach itself to itself automatically,
> using the event name "Form". You have very likely already seen code like
>
>    Public Sub Form_Open()
>      ' ...
>    End
>
> without worrying about it. Well, you don't need to worry about it because of
> the automatic attaching logic that is built into the Form class.
>
> However, if you create a new form and explicitely give it an event name, the
> procedure I described above kicks in. That is, the form is not attached to
> itself as "Form" but to the object which creates the form, with the given
> name (an object can have at most have one primary observer). Consequently,
> Form_Open within the form code will no longer fire. That's what the thread
> was originally about.
>
> Regards,
> Tobi