[GIS] How to connect the selectionChanged signal with pyqt

pythonqgisqgis-plugins

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 so far:

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

In the logs of QGIS I get this warning:

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

can you help me?

Best Answer

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)

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It looks as though your problem is where your functions are defined. You should define all your functions at the beginning of your script, after the import, rather than inside of another function. If you need to use a function inside another, define it first and then call it within the second function. For example, you call lanza() in your first function, but you don't define it until afterwards. Rearranging your functions would take care of the basic Python problems. Any other problems would have to be answered by someone with more QGIS Python experience than I have :).

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I've tested the attributeValueChanged SIGNAL in a created-from-scratch test plugin using QGIS v.2.6.1

You can connect the SIGNAL to your slot this way (I did it in my run() method):

def run(self):
    self.lyr = self.iface.mapCanvas().layers()[0]
    self.lyr.attributeValueChanged.connect(self.mySlot)

And then, you have two options to write your slot (see mySlot and mySlot2):

def mySlot(self):
    QMessageBox.information( self.iface.mainWindow(), "Test", 
        "Attributes were changed!!!", QMessageBox.Ok )

def mySlot2(self, fid, idx, v):
    QMessageBox.information( self.iface.mainWindow(), "Test", 
        "Attributes changed for feature " + str(fid), QMessageBox.Ok )

Both slots work, just replace self.mySlot by self.mySlot2 in the connect method above if you want to switch between them.

If you want to get the test plugin, run it on your QGIS, and have a look at the code, you can access to it here. You find installation and usage instructions in the README file.

Best Answer

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