Add attributes to layer

Question

I'm trying to add a new attribute to a vector layer in my plugin. But it does not work.. Why?

selectedLayerIndex = self.dlg.comboBox.currentIndex()
selectedLayer = layers[selectedLayerIndex]
name = "newAttribute"
selectedLayer.dataProvider().addAttributes([QgsField(name,QVariant.Double)]) 
self.selectedLayer.updateFields()
#or
self.selectedLayer.commitChanges()

• ArMoraer: You are first using the selectedLayer variable, then self.selectedLayer. Those are note the same variables. Is this intended? This may be the cause of your issue.
• Евгения Сидоренко: I have tried in different ways, do not get any!
• okorkut: Have you started editing by selectedLayer.startEditing()?
• Евгения Сидоренко: yes, i tried it
• Евгения Сидоренко: i think problem in this command selectedLayer.dataProvider().addAttributes([QgsField(name,QVariant.Double)]), becauce without it code goes down and work!

Answer 1

This example work perfectly.

from PyQt4.QtCore import *
lyr = iface.activeLayer()
lyr.startEditing()
provider = lyr.dataProvider()
provider.addAttributes([QgsField("newAttribute", QVariant.Double)])
lyr.updateFields()
lyr.commitChanges()

• Евгения Сидоренко: but not in plugin
• Fran Raga: why not?this code work in a plugin or in qgis console.You probably need check your plugin.If you need examples of addatributes etc..Check this class github.com/All4Gis/instagram2qgis/blob/master/… and the CreateShape method for example.
• Евгения Сидоренко: something wron in import block, mb?
• artwork21: @Евгения Сидоренко, within the plugin are you importing QVariant, from PyQt4.QtCore import QVariant

Answer 2

I once had issues using the currentIndex() method (which might be unrelated to the issue you have). Instead, I use the currentText() method to identify the layer and add attribute fields:

from PyQt4.QtCore import QVariant
selectedLayerIndex = self.dlg.comboBox.currentText()
selectedLayer = QgsMapLayerRegistry.instance().mapLayersByName(selectedLayerIndex)[0]
name = "newAttribute"
selectedLayer.dataProvider().addAttributes( [ QgsField(name, QVariant.Double) ] ) 
selectedLayer.updateFields()