[QGIS-Developer] show error message without exiting the plugin

[Roberta Fagandini]

Hi all,
I'm developing a plugin and I need to check if some features of the input
vector layer are selected or not. If not I'd like to show an error message
without closing the plugin gui:

This is the code at the moment:

            if self.dlg.checkBox.isChecked():
                check_sel = selectedLayer2.selectedFeatureCount()
                if check_sel > 0:
                    intersec_layer =
QgsProcessingFeatureSourceDefinition(selectedLayer2.id(), True)
                else:
                    self.iface.messageBar().pushCritical("Error", "No
features selected in layer {}.".format(selectedLayer2.name()))
                    return

Any idea?

Thanks
Roberta
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