[QGIS-Developer] Drag and drop to PostGIS crash

Radim Blazek radim.blazek at gmail.com
Thu Jun 1 10:31:30 PDT 2017

On Tue, May 30, 2017 at 11:39 PM, Nyall Dawson <nyall.dawson at gmail.com> wrote:
>> DD works within the browser now but not for layer with measures.
> I guess this has never been implemented. Looking at ...

I added Z, M and ZM types to postgres provider output and allowed
AddFeatures for layers with measures (user should be warn on
application level).

>> DD from layer tree to postgres/browser imports the layer (without measures) but:
>> - the layer is removed from layer tree - intended?
> Definitely not - I hit this too a week or so ago, and it's far from
> ideal! QgsDockBrowserTreeView::dragEnterEvent/dragMoveEvent/dropEvent
> has code which is supposed to force a copy action when dragging from
> the layer tree, but something's broken there. Any ideas Martin?

I found that it makes copy (showing + icon) if dragged with Ctrl. No
idea why setDropAction( Qt::CopyAction ) in QgsDockBrowserTreeView is

I have no clear opinion if default action should be copy or move in this case.

>> One traceback below, it crashed when DD failed. I think that the
>> problem is that it is trying to show an error message which can only
>> be done on main thread?
>> The code which is run from QgsTaskManager should never interact with GUI?
> That shouldn't be the case (unless there's a bug somewhere). It's true
> that tasks should never interact with the GUI in their run()
> implementation, but QgsTask::finished should only ever be called from
> the main thread and it should be safe to do GUI operations there. From
> your crash below it seems like it's crashing after
> QgsVectorLayerExporterTask::errorOccurred is emitted - but that's only
> ever done from QgsVectorLayerExporterTask::finished . Could you try
> putting a temporary assert in QgsVectorLayerExporterTask::finished to
> ensure that it's working as designed and being called from the main
> thread?

You are right, errorOccurred is emitted on the main thread.
Unfortunately I cannot reproduce the crash. It may have something to
do with how the items in the browser were created, if all pushed to
main thread or deleted to early instead of deleteLater().


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