I've been working on a small plugin recently and I wanted to add a progress bar to it, since there are tasks in this plugin that take some time to complete. I looked at this and this, but so far I've encountered a problem which I can't seem to solve.
Whenever I run the plugin without moving it to another thread, it runs perfectly fine, everything works (but the GUI is unresponsive for a short while). But when I move the worker (the python class that does the heavy lifting) to another thread, suddenly, I can't seem to add the QgsVectorLayer (which is a memory layer) to the iface.LegendInterface anymore. Everything else still works fine, but the layer just does not show up in the legend in QGIS. So far, this is my code, I've left out the specific methods and imported code, since that all works if I don't move it to a thread (so I figure that can't be the problem):
# import some modules used in the example from PyQt4 import QtCore from qgis.core import * from qgis.gui import * import utility_functions as uf import traceback class Worker(QtCore.QObject): def __init__(self, iface, data, layer, plugindir, outfile): QtCore.QObject.__init__(self) self.iface = iface self.data = data self.layer = layer self.plugindir = plugindir self.outfile = outfile self.killed = False self.PathLayer = None finished = QtCore.pyqtSignal(object) error = QtCore.pyqtSignal(Exception, basestring) progress = QtCore.pyqtSignal(float) layerCreated = QtCore.pyqtSignal(object) # tried for debugging, does not work def run(self): ret = None try: # Create edgelist edgelist = self.selectEdges() # Select features on layer and copy to new layer features = self.selectFeatures(edgelist, self.layer)
Everything works perfectly fine up until here. In the method 'createNewLayer', the memory layer should be (1) created using
QgsVectorLayer, and (2) Loaded using
self.createNewLayer(features) # Apply layer style if not self.PathLayer: lyr = uf.getLegendLayerByName(self.iface, 'Path') else: lyr = self.PathLayer self.applyStyle(lyr) if self.killed is False: self.progress.emit(len(self.data)) ret = 1 except Exception, e: # forward the exception upstream self.error.emit(e, traceback.format_exc()) self.finished.emit(ret)
But somehow, the moving to another thread messes with the layer and it can't be added. What's even weirder: I can see the layer when I type into the QGIS python console:
QgsMapLayerRegistry.instance().mapLayers(). So I'm guessing that the way QThreads work, messes up the
QgsMapLayerRegistry OR the
I'm working on macOS Sierra, QGIS 2.14, but I've also tried the plugin on a W10 machine, QGIS 2.18, same problems.