Creating an empty wx.dataview.DataViewColumn

[John Jackson]

(Reposted because I miss-threaded it.)

Is there a (correct) method for creating an empty wx.dataview.DataViewColumn?

In the examples in the demo, the data for the model is always available before the wxpython DataViewColumn is instantiated. (I have an app where I don't have the data until after the control has already been displayed.)

I have tried passing empty lists (no luck!) and have fallen back on passing a row of empty strings, instantiating the control, and then selecting the (only) row and deleting it. But that seems crude.

Is there a cleaner way?

thanks,

John

[Gadget/Steve]

John,

Not really an answer but I would be tempted to display a static text,
the same size & place as you are expecting the DataViewColumn to be,
with the text "Awaiting Data" or some appropriate alternative, and then
replace it with the control once you have some data. I think that might
be cleaner and more user friendly.

Gadget/Steve

[Robin Dunn]

On 8/25/11 3:27 PM, John Jackson wrote:
> (Reposted because I miss-threaded it.)
>
> Is there a (correct) method for creating an empty wx.dataview.DataViewColumn?
>
> In the examples in the demo, the data for the model is always available before the wxpython DataViewColumn is instantiated. (I have an app where I don't have the data until after the control has already been displayed.)
>

Is the problem that you do not know how many columns there will be or is
it just that there is no data to be displayed yet? For the former you
should be able to set up your columns at any time. For the latter I
think you can just return 0 from the model's GetCount method until you
have data.

--
Robin Dunn
Software Craftsman
http://wxPython.org

[John Jackson]

I know the columns and have been setting them up; it's the data isn't available yet.

But over-riding the GetCount method until the data is set seems even hokey-ier than deleting a fake row. How would I know that the count shouldn't be zero, if the user were able to delete the data by some mechanism?

The most natural thing to me would be to pass either an empty list or an empty list of lists.

Can you give or figure out how to do this with the sample (DVC_IndexListModel), so that a button can be used to set the data?

The DataViewListCtrl does work this way, as its data can be added later. Perhaps I need to look under the covers and see how it is doing it, as it is (according to the docs) a wrapper for DataViewCtrl.

Looking at the DVC_IndexListModel, I can see that GetCount would return 0 if self.data was [ ]; though the example
has

def GetColumnCount(self):
return len(self.data[0])

which in't going to work very well if self.data = [ ].

Perhaps there's a better way to return the column count. (An attribute set in the instantiation, or as columns are added?)

BTW: the only reason I am doing is this, is that the DataViewListCtrl sample (DVC_ListCtrl) only sorts on the first column; I don't know if this is a bug or by design. Perhaps it's a bug, as the other column headers show the arrows claiming they are sorting but they actually aren't.

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[John Jackson]

I worked with the demo, and was able to get this to work:

I modified the init for the model to be passed the number of columns in the model, and to handle no data:

class TestModel(dv.PyDataViewIndexListModel):
def __init__(self, data, log, defaultcolumns):
if data:
rowcount = len(data)
else:
rowcount = 0
# dv.PyDataViewIndexListModel.__init__(self, len(data))
dv.PyDataViewIndexListModel.__init__(self, rowcount)
self.data = data
self.log = log
self.defaultcolumns = defaultcolumns

I modified OnAddRow to test if the model had data, and if not, use a curcount of 0:

def OnAddRow(self, evt):
# Add some bogus data to a new row in the model
self.log.write("OnAddRow\n")
if self.model.data:
id = len(self.model.data) + 1
else:
id = 1
value = [str(id),
'new artist %d' % id,
'new title %d' % id,
'genre %d' % id]
self.model.AddRow(value)

(this fixes an out by one bug that I reported as http://trac.wxwidgets.org/ticket/13426 )

In the model, I changed AddRow to create the data if it doesn't exist:

def AddRow(self, value):
if not self.data:
self.data = [value]
else:
# update data structure
self.data.append(value)
# notify views
self.RowAppended()

I modified GetColumnCount:

# Report how many columns this model provides data for.
def GetColumnCount(self):
if self.data:
self.log.write('GetColumnCount: %d' % len(self.data[0]))
return len(self.data[0])
else:
self.log.write('GetColumnCount: Default %d' % self.defaultcolumns)
return self.defaultcolumns

I modified GetCount in case data was None:

# Report the number of rows in the model
def GetCount(self):
if self.data:
rowcount = len(self.data)
else:
rowcount = 0
self.log.write('GetCount: %d' % rowcount)
return rowcount

When the model is instantiated:

# Create an instance of our simple model...
if model is None:
self.model = TestModel(data, log, defaultcolumns=4)
else:
self.model = model

I then instantiate without any data:

# win = TestPanel(nb, log, data=musicdata)
win = TestPanel(nb, log, data=None)
return win

This works.

However, deleting rows doesn't update the view(s). Adding rows does. I reported this as http://trac.wxwidgets.org/ticket/13427 .

[Robin Dunn]

On 8/26/11 1:04 PM, John Jackson wrote:
> I know the columns and have been setting them up; it's the data isn't available yet.
>
> But over-riding the GetCount method until the data is set seems even hokey-ier than deleting a fake row. How would I know that the count shouldn't be zero, if the user were able to delete the data by some mechanism?
>
> The most natural thing to me would be to pass either an empty list or an empty list of lists.
>
> Can you give or figure out how to do this with the sample (DVC_IndexListModel), so that a button can be used to set the data?
>

As you've discovered with your modifications to the sample mentioned in
the other message, a model does not have to always use a list to hold
the data. It is intended to be a completely independent interface
between the view and whatever data it is displaying. The use of a list
in the example is just that, an example, or you could think of it as an
implementation detail. From the perspective of the DVC it is almost
totally irrelevant how the model is implemented, only that it does
implement the required interface.