How to connect the selectionChanged signal with pyqt?

Question

Hi I am developing a plugin for Qgis in python, I need to connect the sselectionChanged signal emitted when a feature of the layer is selected, I could not find any examples on internet, here is what I have done as far

    QObject.connect(self.iface.mapCanvas(),SIGNAL("selectionChanged(QgsMapLayer)"), self.test) 

on the log of qgis I get this warning:

    Warning: Object::connect: (receiver name: 'MainWindow')

can you help me? please, thanks in advance

Answer 1

arpho, this new style PyQt connection works for me in PyQGIS Console (Mac OS X 10.7.3, with QGIS 1.7.4)...

def test(layer): print "selection changed"

qgis.utils.iface.mapCanvas().selectionChanged.connect(test)

I had to hit return at an empty prompt to see the printed "selection changed" messages. If I changed the selection multiple times, those would show up upon hitting return.

The only thing I can see that might cause that error is if your 'self' object hasn't had the iface reference assigned. Is this in your __init__() method of your plugin's class?:

self.iface = iface

Or, that iface hasn't been passed to your plugin's class. Check your __ini__.py file for your plugin to make sure it's being passed as an argument to your plugin's class in the def classFactory() method.

Example:

def classFactory(iface):
    from my_plugin import MyPlugin
    return MyPlugin(iface)

Answer 2

Hi thanks for your answer; I did what you said in the python console of qgis and it works; I tried to make it work on my plugin. this is an extract of my code:

def __init__(self, iface):
    # Save reference to the QGIS interface
    self.iface = iface
    self.tree=Tree()
    self.progressBar=ProgressBarWindow(True,True)
    self.progressBar.setMaximumOverall(4)
    self.ui_tree=MainWindowAlbero(iface)

def selectedChanged(self,t):
    self.ui_tree.etichetta.setText(t)

def run(self):
    self.iface.mapCanvas().selectionChanged.connect(self.selectedChanged("selected"))

when I launch the plugin I get this error

TypeError: connect() slot argument should be a callable or a signal, not 'NoneType'

why my function is a NoneType?> is not the first time I connect a signal to a method, I do not understand the problem