Standalone app does not show the content

Question

I am trying to show the shapefile in canvas using standalone application. However it does not show the content. Here is my code and I am using PyQt5, Qgis 2.99, PyCharm 3.6

from qgis.core import *
from qgis.gui import *
from qgis.utils import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *

app = QgsApplication([], True)
path = "C:/Users/DELL/AppData/Roaming/QGIS"
app.setPrefixPath(path, True)
app.initQgis()
canvas = QgsMapCanvas()
title = "PyQGIS Standalone Application Example"
canvas.setWindowTitle(title)
canvas.setCanvasColor(Qt.white)
layer_info = "C:/Users/DELL/Desktop/GIS_CensusTract_poly.shp"
layer = QgsVectorLayer(layer_info, 'MyShp', "ogr")
layer.updateExtents()
QgsProject.instance().addMapLayer(layer)
canvas.setExtent(layer.extent())
canvas.setLayers([layer])
canvas.zoomToFullExtent()
canvas.show()
exitcode = app.exec_()
QgsApplication.exitQgis()
sys.exit(exitcode)

Answer 1

Most times if your prefix path is wrong, the map fails to display. Try changing your paths to

qgis_prefix="C:\\Program Files\\QGIS\\apps\\qgis"  
                    OR
qgis_prefix="C:/OSGeo4W64/apps/qgis"              # if running from OSGeo4W

QgsApplication.setPrefixPath(qgis_prefix, True)