QGIS Processing Progress

Question

I have been developing a python plugin that uses Processing algorithm for raster calculations. I want to support the gui with progress bar. How can i connect Processing job to progress bar? I found little description in here but no success.

Answer 1

Here is a way to set a primitive progress bar. Design is based on example you can found within the PyQgis Dev. Cookbook (see section 11.2)

Example is designed to work with features of a QgsVectorLayer but it shows the main steps you could adapt for your process algo.

The key to your problem is to find a way to evaluate the progression of your algo within itself.

1.Progress Bar is created outside of your processing function

2.Progress Bar is updated inside your processing function

I pass it to the iface.messageBar() to make it easy

import time

#clear the message bar
qgis.utils.iface.messageBar().clearWidgets() 
#set a new message bar
progressMessageBar = qgis.utils.iface.messageBar()

######################################
# Prepare your progress Bar
######################################
progress = QProgressBar()
#Maximum is set to 100, making it easy to work with percentage of completion
progress.setMaximum(100) 
#pass the progress bar to the message Bar
progressMessageBar.pushWidget(progress)


#get a vector layer
vlayer = QgsMapLayerRegistry.instance().mapLayer("your layer")
vlayer.selectAll()

#Count all selected feature
count = vlayer.selectedFeatureCount()
#set a counter to reference the progress
i = 0

#start your processing loop
for feature in vlayer.selectedFeatures():
    ######################################
    #Update the progress bar
    ######################################
    i = i + 1
    percent = (i/float(count)) * 100
    progress.setValue(percent)
    #optionnal, make your processing longer to enjoy your process bar :)
    time.sleep(1)

    ######################################
    #Do your processing stuff
    ######################################

qgis.utils.iface.messageBar().clearWidgets()  

Answer 2

If you would like to connect a Processing job to a progress bar, you can supply the progress bar using the progress parameter:

buff_res = processing.runalg("qgis:fixeddistancebuffer",
                             self.inpvl, 10, 10, True, None,
                             progress=myprogress)

See also: https://gis.stackexchange.com/a/237282