[Gambas-user] A Gambas odissey

Fabien Bodard gambas.fr at ...626...
Tue Aug 12 12:53:40 CEST 2008

is this can help you ?

This a simple demo off event management via objerver object that catch
the event before object.

If you have others question tell me


2008/8/12 Fabien Bodard <gambas.fr at ...626...>:
> hohoooo there is many thing wrong here !
> 2008/8/11 Doriano Blengino <doriano.blengino at ...1909...>:
>> Hello all...
>> I am writing a file manager, hybrid between FileRunner and a more
>> modern one.
>> I started with a DirView, and soon discovered that it doesn't raise the
>> KeyPress event (but the IDE makes you think that).
> dir view is a top level component you can easily rewrite it
>> There were other
>> things missing in DirView, so I wrote my MyDirView the way I wanted. It
>> was easy at first, but then I discovered that it is difficult, or at
>> least not clear, how to move the "Current" cursor. I am not sure why,
>> but it does work by setting the Selected property of an item. I failed,
>> instead, in removing all the children of an item, one by one (there is a
>> clear() method, but I need to delete them one by one). The "for each ...
>> in item.children" does not work; it is not the first time I see similar
>> anomalies, especially while stepping the source.
>> Writing MyDirView revealed another problem. If in a custom control I
>> receive the KeyPress event, I can not re-raise it (stack overflow). So I
>> have to raise another event with a different name. This breaks the
>> consistency of naming - in a row of four controls, each derived from the
>> other, the same event must be called with four different names. I took a
>> look at the FileView control to see what has been done in there. It
>> receives Click events, and raises Click events. What inside? It does not
>> inherit from ListView or similar. Now I understand why it works, but I
>> don't like it.
> it don't have to inherit it's a composed widget..; not an extention.
>> Anyway, I went ahead. I put two FileView on the form. They don't raise
>> KeyPress event. It's getting tiring. I don't want to rewrite MyFileView
>> just now (I will do, because I need more functionalities). I only need
>> to catch Backspace and Enter, so I make a menu voice which has the
>> Backspace key as its shortcut. Now the backspace works, but... how the
>> hell can I tell which control is focused? The only way I found was to
>> catch the GotFocus and LostFocus events, and track the focus by hand. I
>> have only three controls, but what about if I had dozens of them?
>> Grouping them would group all their events, while I am interested in
>> grouping only GotFocus/LostFocus events.
>> To make it short, I succeded in make it work, and passed to the
>> Enter key. The Enter key should invoke the selected file in one of the
>> two FileView's. A menu voice has only one shortcut, but the Enter keys
>> are two (Gambas calls them Enter and Return). Uhm... no way. Then I try
>> to use the Form_Keypress event, but it does not fire - the controls are
>> stealing the keys. So, there is no way to do this thing. If a FileView
>> does not "activate" a file when the user presses Enter, then you can not:
>>    1: inherit a new control which does, because you must rename all its
>> events
> what about observer ?
>>    2: use a menu voice to do it, because a menu voice has only one
>> shortcut; if you want use more keys, no way
> ???
>>    3: use the form KeyPress, which does not fire
>> The only way left is to create a new control, and then instantiate a
>> FileView inside it. This is not inheritance, because you have to
>> replicate all the things you need: events, properties, methods.
>> Coming from Delphi, I must say the following:
>> Delphi forms have a KeyPreview property. If you set it, then *all* the
>> keypresses are first passed to the form. The form then decides wether to
>> ignore the key, or make additional things, to let the key pass, or to
>> stop it.
>> Delphi containers have an ActiveControl property which tells which
>> control has the focus. Moreover, every control has a Focused property
>> which tells if a specific control has the focus or not. The list of
>> things Delphi has and Gambas doesn't is long, but I don't want to
>> criticize. I am really missing keyboard and focus control. It seems that
>> VisualBasic programmers use the mouse a lot, and neglect keyboards, and
>> so do many users, so this could be the reason why Gambas seems to do the
>> same.
>> I don't know Gambas very well, and I could have missed a lot of things.
> many
>> But it is easy to miss things - in the documentation a "See also"
>> section in every topic could really help.
> there is
>> Finally, I must say that I think, and *repeat*, I think, the event
>> management is wrong or, at least, it is not as flexible as it could be.
>> Once a control raises event, you can not make it stop.
> not true ... it's STOP EVENT
>>If you group
>> controls, you group all their events.
> yes it's an event handler grouping, not a true group ... to doing a
> group you need to store objects in an array
>> Once you assign a handler to an
>> event, you can no more change it.
> wrong : Object.attach(Object, parentclass, "handler name")
>> Probably Gambas is too developed to
>> change things at this point but, for who cares or is courious, I will
>> explain how events work in Delphi. An event in delphi has an associated
>> property which contains the address of a routine to launch. For example,
>> if a control has a Click event, then it has a OnClick property. That
>> property contains the address of the routine to invoke when the control
>> wants to "raise" the Click event. The OnClick property is a procedural
>> type, a thing that does not exist in Gambas.
> true ... gambas is a true oriented object language
>> But being a property, the
>> main program can disable that event by setting that property to NIL
>> (NULL),
> PUBLIC SUB MyList_KeyPress()
> But it's true that we can't turn off an event
>> or change the handler by setting the property to another value.
>> It is possible to associate many controls to the same handler, but only
>> the events we want, not *all* the events of *all* the selected controls.
>> In fact, events do not exist in delphi, they are simply procedure calls.
>> Instead of writing:
>>    raise KeyPress   ' Gambas code
>> which, I suppose, unleashes a textual search for a public subroutine
>> named in some correct way, in Delphi one would write:
>>    if OnKeypress<>NIL then OnKeypress();   // procedural call
>> This paradigm is faster, more sure, more flexible, more easy to
>> understand. When deriving controls, the derived one can override the
>> methods of the ancestor, and still call the inherited one. Gambas has an
>> interesting feature which does the opposite: instead of calling the
>> ancestor method on demand, it can stop it on demand. It is quite the
>> same, I think.
> ok got it in fact
>> Happy holidays to everyone.
> to you too
> Fabien
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