On 27 September 2016 at 03:12, Matthias Kuhn <[email protected]> wrote: > Hi Andreas > > On 26/09/16 16:01, Neumann, Andreas wrote: >> >> Hi, >> >> I recently had the need to filter a layer based on a selection, e.g. >> for QGIS atlas. The expressions plus plugin provides the >> "isselected(layername)" function which returns true|false for each >> feature - based on the selection state. >> >> Could we make this a core expression in QGIS without the need to >> install a plugin? I guess this expression is of quite common use for many. >> > > At the time I implemented this there were no expression variables > available and an "expression context" barely existed and therefore a > proper solution was out of scope, so it was more suitable to ship it > with a plugin than in core. > > With the current state of expressions it should not be hard to implement > it in a clean way. > > Proposal: > isselected(feature, layer_id) <-- explicitly check for a certain feature > on a certain layer > isselected(feature_id, layer_id) <-- explicitly check for a certain > feature on a certain layer > isselected() <-- shorthand for the current feature / layer from the > expression context.
Sounds good to me. As much as I hate the idea of styling based on something as transient as a selection there's obviously demand for this, so as long as it's done in the right way (using contexts) I'm not against it. The is_selected() method could even use a scoped expression function provided by the layer scope to avoid the need to retrieve layers by id. Just a note that it would need to be "is_selected(...)" to keep the standard naming of other expression functions. Maybe this could even be integrated with Nathan's experiments with selection presets... Nyall > > Best regards > Matthias > > _______________________________________________ > Qgis-developer mailing list > [email protected] > List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ Qgis-developer mailing list [email protected] List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer
