Display bug when label contain a expression

Question

I have this function who supposed to change the label of polygon (code below), where "nom_com" and "statutpro" are fields in a layer.

def ETIQUETAGE(self):
    layer = self.COUCHE_DEPARTEMENT_SELECTIONNEE() #return a vector layer
    deco = QgsPalLayerSettings()
    deco.enabled = True
    isExpression = True
    if self.ChoixEtiquetage.currentText() == "COMMUNE":
        deco.fieldName = '\'nom :\' +"nom_com"'
    if self.ChoixEtiquetage.currentText() == "COMMUNE ET STATUT PROSPECTION":
        deco.fieldName = '"nom_com" + \'\\n\' +"statutpro"' 
    labeler = QgsVectorLayerSimpleLabeling(deco)
    layer.setLabeling(labeler)
    layer.setLabelsEnabled(True)
    layer.triggerRepaint()

When I run it everything ok (i don't have any error), the problem is for the display. The function change the label charateristic in the properties window but there is no display until I press aply in the properties window.

When I put only one argument the display work perfectly. for example

deco.fieldName = "nom_com"

Is there a particular syntax when it's a expression ?

Answer 1

I just see where my error was, it was a syntaxe error. If the label is expression based we must put

deco.isExpression

for the plugin to display something in the canvas

def ETIQUETAGE(self):
layer = self.COUCHE_DEPARTEMENT_SELECTIONNEE() #return a vector layer
deco = QgsPalLayerSettings()
deco.enabled = True
deco.isExpression = True
if self.ChoixEtiquetage.currentText() == "COMMUNE":
    deco.fieldName = "concat('nom : ', nom_com)"
if self.ChoixEtiquetage.currentText() == "COMMUNE ET STATUT PROSPECTION":
    deco.fieldName = "concat('nom : ', nom_com, '\\n', 'Statut prospection : ', statutpro)"' 
labeler = QgsVectorLayerSimpleLabeling(deco)
layer.setLabeling(labeler)
layer.setLabelsEnabled(True)
layer.triggerRepaint()

hope it will help people