[Gambas-user] Does ListBox ''_MouseDown()" Event work ?

[Bruce Steers]

On Sat, 9 Dec 2023 at 10:51, Gianluigi <gradobag at gradobag.it> wrote:

> Il 09/12/23 10:45, Claus Dietrich ha scritto:
>
> >* Le 08/12/2023 à 14:06, T Lee Davidson a écrit :
> *>* > On 12/7/23 20:13, vuott--- via User wrote:
> *>* >> Hello,
> *>* >> the ListBox ''_MouseDown()" Event does not work for me.
> *>* >>
> *>* >>
> *>* >> [System]
> *>* >> Gambas=3.18.90 38b49c0 (master)
> *>* > [snip]
> *>* >
> *>* > The issue exists with v3.18.4 as well. Interestingly, a double-click
> *>* > triggers the MouseDown event with both Qt5 and GTK3.
> *>* >
> *>>* Compound non-native controls usually eat some of the low-level events.
> *>>* You should normally never try to handle low-level events on complex
> *>* controls.
> *>>* Regards,
> *>>* --
> *>* Benoît Minisini.
>
> This reply made me curious and I would be grateful if somebody
> can provide some background and help me to understand:
> What are possible reasons that non-native controls "eat some of the low
> evel events"?
> Why should I never try to use events which are a documented capability
> of a control?
> Shall I regard it as normal that I can only access an event if I add
> additional code as proposed by Bruce?
> I am asking this, because I program controls myself (beginner level) and
> so far didn't have the experience, that events fail - unless I forgot
> to raise them.
>
> Best regards
> Claus
> *
>
> Hi Claus,
>
> you're not the only one who was baffled by Benoit's response.
>
> We discussed this with other users of the Italian forum and like you we
> are all curious.
>
> With best regards
>
> Gianluigi
>

It made perfect sense to me as I myself have written many compound
controls.  There is much excessive code needs to be added to make all
compound controls trigger all standard control events.

Like Benoit explained gambas unique controls (from gb.gui.base, and some
gb.form) are made by using a container, maybe a panel, then various other
controls placed inside.

In order to make something like MouseDown trigger no matter where you click
you have to make a MouseUp event for every added control inside the
container.

a ListBox for example is actually a gridview inside it's own container.

internally the gridview gets its events inside the listbox.
The listbox itself only has 3 events..
Event Click
Event Activate
Event Select

The Click event for example is not just the gridviews click event.
the listbox creates a timer on the gridviews Change event and then triggers
it's own Click event.

Things to consider about you bafflement...
there are many different gambas compound controls made with many different
combinations of objects.

the code would have to be filled with many lines like this..

Public Sub IntrnalTextBox_MouseDown()

  Raise MouseDown

End

Public Sub IntrnalLabel_MouseDown()

  Raise MouseDown

End

Public Sub IntrnalPanel_MouseDown()

  Raise MouseDown

End

So imagine having that (and having to do that) for every gambas controls
internal objects and for every standard event.
that's going to be a lot of bloating.


Possible solutions for you Ben....

some sort of event , er , upstreamer, for want of a better word.
a new property for controls, something like ContainerTriggers or something
So if i set InternalLabel.ContainerTrigger = True it will auto try to..
Object.Raise(Me._Container, sEventName)
(you know what i mean)

or..
A way to hide all the events of Control.class from UserControl.class as
they are not all really supported by the control.
Because in the IDE if i type Public Sub ListBox1_  then i get a list of all
Control.class events.  even though only some of the events will actually do
anything. and can be unexpected like the ListBox_MouseDown example that
does actually fire for some reason with a double click.

That might at least make things clearer for the programmer.


Possible solutions for us..
Understand there is a difference with a toolkit control and a gambas
compound control.  (i guess it should be documented better)

As i previously mentioned all gambas compound controls have a way to access
and Observe the events of the internal object should you want to do
anything fancy.
see Observer.class and Watcher.class  (definately avoid using
Object.Attach() as this will break stuff for sure)

As Benoit mentioned there are risks with doing this as the control is using
it's internal events as it needs to and if you have not studied the
controls code you may interfere with it's internal workings.
But if you study the controls code in gb.gui.base or gb.form or whatever
then you can probably modify.  auto-inheritance can be a good way to modify
compound control events.


Some food for thought. :)

Respects
BruceS
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