[Gambas-user] TableView Tag Property

[Tobias Boege]

On Wed, 13 Jan 2021, Martin wrote:
> Hi,
> 
> Tableview has not Tag property for each cell, but is there some way to add
> this property to it?
> 
> The point is that when I click on a cell I want it to change its image to
> show another state, which is easy using the mousedown event, for example,
> but when is necessary to save the state data on a support, such as a
> database where is the info?
> 
> It seems that there is no place to extract the true or false information.I
> currently use the .WordWrap property but it's not the right thing to do I
> guess, .Tag would be the optimal solution.
> 
> What could be the solution? Change the components [Grid|Table]View ? or ...
> Made a modified component?
> 

This is indeed sometimes an inconvenience in Gambas. A Tag property can
be useful for remembering external information inside a control or any
object, but that property exists only sporadically.

The clean and proper way around this is to make a new control class.
Apparently TableView is not made to hold all the information you want
to associate with a cell. So make a custom control based on TableView,
which has an internal Array or Collection indexed by the cells which
stores the additional data and presents a convenient interface to it.
Look at how TableView.class in gb.form wraps the GridView class to
add functionality to it.

That is more work than having Benoît add a Tag property and waiting for
the next stable Gambas version. It may be more work than you want to do.
Alternatively, here is a hack that I believe should work: TableView is
essentially a GridView, which is a control implemented in Gambas as of
some much earlier version of Gambas 3.

A cell in a TableView is of type _GridView_Cell. It is a completely
ordinary Gambas class (as opposed to a native virtual class if it had
been implemented in a gb.qt or gb.gtk component, but I digress...).
This means that you can *extend* the _GridView_Cell class by over-
riding it in the global symbol table [1].

Basically: add a class named _GridView_Cell to your project and mark
it Export. Then just add "Public Tag As Variant" inside the class,
nothing else is needed. You do not have to re-implement the cell or
copy it over from gb.form; the interpreter will automatically merge
your version *into* the one from gb.form. This way you replace the
normal cell class with your extended version all throughout the
current Gambas process, so everything that uses a _GridView_Cell
will now transparently have this additional public variable Tag.

I haven't tried it myself, but I think it should work.

Best,
Tobias

[1] http://gambaswiki.org/wiki/doc/object-model#t21

-- 
"There's an old saying: Don't change anything... ever!" -- Mr. Monk