Displaying progress bar when using QGIS processing tool

Question

I'm building a QGIS plugin and I want to improve the user interface. I'm able to use processing tools like buffer, but with heavy layers I want to display a progress bar, users can easily see the treatment progression.

In documentation, there is some words about it but when I run simples examples, QGIS systematicaly not responding and there isn't any progress bar. Note that this treatment works perfectly without this progress bar issue.

Here is my code :

import time
from qgis.PyQt.QtWidgets import QProgressBar
from qgis.PyQt.QtCore import *

# Progress bar
progressMessageBar = iface.messageBar().createMessage("Work in progress...")
progress = QProgressBar()
progress.setAlignment(Qt.AlignLeft|Qt.AlignVCenter)
progressMessageBar.layout().addWidget(progress)
iface.messageBar().pushWidget(progressMessageBar, Qgis.Info)

# Layer
vlayer = qgis.utils.iface.activeLayer()
count = vlayer.featureCount()
features = vlayer.getFeatures()

# Progression loop
for i, feature in enumerate(features):    
    percent = i / float(count) * 100
    # My treatment
    processing.runAndLoadResults('native:buffer', {"INPUT": vlayer, "DISTANCE": 20, "OUTPUT": 'memory:buffer'})
    # Progression status
    iface.statusBarIface().showMessage("Processed {} %".format(int(percent)))
    progress.setValue(percent)

iface.statusBarIface().clearMessage()

Am I missing something ? Maybe something is wrong in my loop. I'm working with QGIS 3.10.1.

Answer 1

With researches, i made this acceptable answer, without any loop. I assign QgsProcessingFeedback() to QProgressBar() and get a dynamic progression bar when processing is running :

# Progression bar
qgis.utils.iface.messageBar().clearWidgets()
progressMessageBar = qgis.utils.iface.messageBar()
progressbar = QProgressBar()
progressMessageBar.pushWidget(progressbar)

# Processing feedback
def progress_changed(progress):
    #print(progress)
    progressbar.setValue(progress) 

f = QgsProcessingFeedback()
f.progressChanged.connect(progress_changed)

# Layer and processing
vlayer = qgis.utils.iface.activeLayer()
processing.runAndLoadResults('native:buffer', {"INPUT": vlayer, "DISTANCE": 20, "OUTPUT": 'memory:buffer'}, feedback=f)

# Clear the message bar when done
qgis.utils.iface.messageBar().clearWidgets()

Thanks to all, you put me on the good track.