[RQt-devel] How to delete a layout in an existing widget?

[Michael Lawrence]

On Mon, Apr 11, 2011 at 10:54 PM, Tengfei Yin <yintengfei at gmail.com> wrote:

> Hi Michael,
>
> Thanks,
>
> I am not sure which object should be set to NULL.
>
> > trackWidget <- Qt$QWidget()
> > trackLayout <- Qt$QGridLayout()
> > trackWidget$setLayout(trackLayout)
> NULL
> > trackWidget$layout()
> QGridLayout instance
> > trackWidget$layout() <- NULL
> Error in trackWidget$layout() <- NULL :
>   invalid (NULL) left side of assignment
>
>
I just meant set the layout reference of the widget to NULL.

trackWidget$setLayout(NULL)


> The layout() return a instance and it looks like it cannot be set to NULL.
>
> My case may sounds weird, I changed view object to referecne class, say obj
> is a view object, obj$pars$seqname <- "chr3", will change the visualized
> chromosome and emit a signal to re-create multiple tracks for chr3 , I
> actually recreate the scene and view, but only keep the top widget which
> contains all tracks, so it looks like the windows is there, and only the
> view is updated, I am using a widget to embed two scenes in TracksView, this
> design is pretty much like USCSgenome browser, top scene shows a single
> chromosome, never be zoomed, and bottom scene contains multiple tracks,
> which zoom in/out at the same ratio.
>
> To update this widget to visualize a new chromosome, I run the following
> command without creating a new Qwidget
> .....
>  if(is.null(trackWidget)){
>     trackWidget <<- Qt$QWidget()
>   }
> trackLayout <- Qt$QGridLayout()
> trackWidget$setLayout(trackLayout)
> ......
>
> This will give me a error saying the layout exists. it looks like it cannot
> be simply over created.
>
> I just solved the problem by keeping the layout with QWidget, so I simply
> keep the top widget and layout at the same time, only create all scene and
> view and layers, now it works,
>

I think you're saying that you're repopulating the layout. That makes more
sense here. Another option would be to just switch the existing layers to
look at a new chromosome. Why recreate everything?


> I am still wondering how to delete that layout through, in case there is a
> use case in the future, such as update a layout design of one specific GUI
> without destroying it.
>
> Thanks
>
> Tengfei
>
> On Tue, Apr 12, 2011 at 12:15 AM, Michael Lawrence <
> lawrence.michael at gene.com> wrote:
>
>> The memory management is such that the memory will be deleted if there are
>> no references to it from R or a Qt object. The "Qt object" part depends on
>> the type of object being considered for deletion. In this case, a QLayout is
>> a QObject, so it is owned by its parent. The parent is the widget (unless
>> this is a sub-layout). So to delete the layout, you need to set NULL for the
>> layout of the widget and rm() any references from R. And then run gc(). Let
>> me know if that works.
>>
>> Changing the layout of a widget is a bit strange though -- what are you
>> trying to do?
>>
>> On Mon, Apr 11, 2011 at 9:57 PM, Tengfei Yin <yintengfei at gmail.com>wrote:
>>
>>> Hi
>>>
>>> I hope to delete and create a new layout without destroying a widget,
>>> based on Qt documentation,
>>>
>>> If there already is a layout manager installed on this widget, QWidget<http://doc.qt.nokia.com/4.7/qwidget.html> won't
>>>> let you install another. You must first delete the existing layout manager
>>>> (returned by layout <http://doc.qt.nokia.com/4.7/qwidget.html#layout>())
>>>> before you can call setLayout() with the new layout.
>>>
>>>
>>> to add a layout to an existing widgets,  I find something like
>>>
>>> void myWidget::makeLayout()
>>> {
>>>   // Delete old layout (if any)
>>>   delete layout();  // This is QWidget::layout()
>>>
>>>   // Perhaps you have to remove, add, hide or show some childwidgets.
>>>
>>>  .....
>>>   ...
>>> }
>>>
>>> So how to do that in R, I cannot find something like close() or delete()
>>> for QWidget$layout().
>>>
>>> Thanks
>>>
>>> Tengfei
>>>
>>>
>>> --
>>> Tengfei Yin
>>> MCDB PhD student
>>> 1620 Howe Hall, 2274,
>>> Iowa State University
>>> Ames, IA,50011-2274
>>> Homepage: www.tengfei.name
>>>
>>>
>>>
>>> _______________________________________________
>>> Qtinterfaces-devel mailing list
>>> Qtinterfaces-devel at lists.r-forge.r-project.org
>>>
>>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/qtinterfaces-devel
>>>
>>>
>>
>
>
> --
> Tengfei Yin
> MCDB PhD student
> 1620 Howe Hall, 2274,
> Iowa State University
> Ames, IA,50011-2274
> Homepage: www.tengfei.name
>
>
>
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