[Gambas-user] Form listener

[Fabien Bodard]

Dim NForm as Form
NForm = new MyForm(ME) as "MyForm"



the event will fire at :

Public Sub MyForm_KeyPress()

End



2017-05-29 17:34 GMT+02:00 Tobias Boege <taboege at ...626...>:
> On Mon, 29 May 2017, Leon Davis wrote:
>> Using Gambas v3.9.2 and GTK+3
>>
>> I have added a form to another form:
>>
>> Dim NForm as Form
>> NForm = new MyForm(ME) as "MyForm"
>>
>> The problem I'm having is none of the Key events, i.e. (keypress, keyup,
>> keydown) for either form do anything. Also the Form_Resize for NForm
>> doesn't fire. In my search I found an item that mentioned doing a search
>> for listener in the Gambas wiki but that search was unsuccessful. Searched
>> the mailing list with the same result. Any suggestions?
>
> What is your problem exactly; where does the event not fire? But let me make
> a guess to what question you are asking and answer that question.
>
> You want to know why the Form_Resize event in your MyForm class does not
> fire? The reason for this is that you give your NForm instance of the MyForm
> class an event name "MyForm" explicitly (by using As "MyForm").
>
> I'll assume that the above code is executed inside another Form called, say,
> FParent. If you create an object inside FParent and give it an event name,
> as you do above, FParent will become the *default event observer* for that
> object. It will intercept all the events that the object NForm raises and
> these events will be issued under the event name "MyForm" you specified.
>
> Why is this a problem? Normally, forms are their own default event observer,
> under the event name "Form". This is a mechanic hidden inside the Form class
> code -- when a form object is created and detects that it hasn't gotten an
> explicit default event observer, it makes itself its own event observer.
> This is what enables you to normally intercept a Form's Resize event inside
> its own class code, by defining the Form_Resize event handler.
>
> To summarise: because you use the As "MyForm" syntax, you give NForm a new
> default event observer (namely FParent). You can now intercept the events of
> NForm inside the code of FParent, by using the event name MyForm, but you
> *cannot* intercept the events in the MyForm code using the event name Form
> anymore.
>
> The solution is: don't use the As "MyForm" syntax if you want to continue
> receiving NForm's events inside MyForm's class code. Instead you should
> *duplicate* all the events by using an Observer:
>
>   Dim NForm As MyForm
>   Dim hObs As Observer
>
>   NForm = New MyForm
>   hObs = New Observer(NForm) As "MyForm"
>
> Now you have NForm which is its default event observer (so Form_Resize will
> fire inside the MyForm class) and you duplicate all the events that happen
> through the observer, so you also receive the events in FParent, such as
> MyForm_Resize. I believe this is what you mean by "listener", but the
> appropriate Gambas term is "observer".
>
> The article "The Gambas Object Model" [1] in the wiki should be mandatory
> reading for everyone. It feels like I spend more time citing this page than
> anything else I do on this mailing list.
>
> Regards,
> Tobi
>
> [1] http://gambaswiki.org/wiki/doc/object-model#t10
>
> --
> "There's an old saying: Don't change anything... ever!" -- Mr. Monk
>
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-- 
Fabien Bodard