[Qgis-developer] Memory data provider persistence

[Chris Crook]

Yes .. I got carried away and put up a patch implementing the projectWrite signal in the QgisInterface before I saw this alternative.  Though in fact I do think that is makes sense to have a QgsInterface projectSaved() signal matching the projectRead().  And maybe a savingProject() that happens before it is saved.

I forgot about needing to catch changes in the memory provider data to set the dirty state .. This was part of my original plan for implementing the memory provider data into the project file itself but I forgot it in my excitement about a plug in option.  (The excitement is about being to do it now - I still think this really belongs in the core system). 

Maybe if I can trap an event relating to saving edits, then if the edited layer provider is a memory provider I can set the project state to dirty.  And plugins will have to set the dirty state themselves (this may happen anyway, eg when the contour plugin generates a new contour layer adding the layer sets the state).  This is getting a bit messy though!

So maybe there is still some work required to provide the signals for changes to vector provider data.  In fact the project does need to take ownership of the data.  For it all to make sense it needs a projectDataDirty() flag.  Bother!

Chris

-----Original Message-----
From: b.rowlingson at googlemail.com [mailto:b.rowlingson at googlemail.com] On Behalf Of Barry Rowlingson
Sent: Tuesday, 7 December 2010 12:21 p.m.
To: Chris Crook
Cc: Martin Dobias; qgis-developer at lists.osgeo.org
Subject: Re: [Qgis-developer] Memory data provider persistence

On Mon, Dec 6, 2010 at 7:12 PM, Chris Crook <ccrook at linz.govt.nz> wrote:
> Hi Barry et al
>
> Good point about a plugin implementation .. I hadn't thought of that obvious option - definitely one to follow up on.  It might still need a few tweaks in terms of Qgis.  The QgisInterface has a projectRead() signal that could be used to trigger reloading the data, but I don't see a projectSaved() signal to trigger writing.  Easy to add that though, and probably generally useful.

 There's a projectWrite signal:

http://www.qgis.org/api/classQgsProject.html#a935c811d84c51e908c73868be9b69c4

 which seems to be emitted before the layers are saved, so if anything hooked into that wants to make changes it should be able to. Haven't tried, but will that do the job?

> Given that there is a signal to hook in to this is, as you say, a piece of cake.  I'm kicking myself for not having thought of this months ago!!

 The only problem might be if the memory provider doesn't set the project as dirty when it changes itself. Otherwise users could do a 'quit', and then qgis quits without chance to save the project.

> In terms of file location my preference would be something directly related to the project file .. That is obviously easy.  And shapefile is not my choice, just because of the messy bunch of files it creates and having so many of them and because the DBF format is limiting and pretty scungy!  But that is personal preference I guess.

 Agreed! I've been saving things as GML lately.

Barry
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