[QGIS-Developer] how to warn user when when reading project XML

[Nyall Dawson]

On 6 February 2018 at 06:33, Denis Rouzaud <denis.rouzaud at gmail.com> wrote:
> Hi all,
>
> I am wondering what's the best way to warn the user when reading XML is not
> going as expected i.e. when an error is encountered.
>
> Here is the path to the method I want to warn from:
>
> QgsProject::read
> QgsProject::readProjectFile
> QgsProject::_getMapLayers
> QgsProject::addLayer
> QgsMapLayer::readLayerXML
> QgsVectorLayer::readXML
> QgsVectorLayer::readSymbology
> QgsEditFormConfig::readXML
>
> I see only two solutions:
>
> 1. Using success return value and some errorMessage.
>  This is partly done in readSymbology but totally incomplete (always returns
> true and errorMessage are not used at all...)
> It would require a finer grain than bool as return value (info / warning /
> error, probably).
> It would probably be a a list of error messages.
>
> 2. Emitting signals.
> But that means bring the connections all the way up to the project by
> connecting and disconnecting the map layers and all other objects during the
> way down. Moreover, many config object are not QObjects.
>
> To me solution 1. sounds nicer but is an API break.
> The small feature I am working on is targeted to 3.2 si I would need to set
> this in place prior to release.
>
> Is there somehting I am missing?

For those following at home, Denis and I had a quick brainstorm and
settled on the idea of instead extending QgsReadWriteContext to add
error collection/reporting there.

Nyall