VTKWidget in Qt is not updated as expected - qt5

Question

I would like to display a 3D-Animation in my Qt5-Gui. Everything works as expected, but unfortunately the scene is not getting updated when I don't interact with the vtkWidget. In other words: When I want to see the animation, I need to click continously with the mouse on the widget. I'd be greatful for any help.
import sys
import vtk
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5 import Qt
import numpy as np
from vtk.qt.QVTKRenderWindowInteractor import QVTKRenderWindowInteractor
class mainWindow(Qt.QMainWindow):
def __init__(self, parent = None):
Qt.QMainWindow.__init__(self, parent)
self.frame = Qt.QFrame()
self.vl = Qt.QVBoxLayout()
self.button = QtWidgets.QPushButton("TestButton")
self.label = QtWidgets.QLabel("This is a label")
self.vtkWidget = QVTKRenderWindowInteractor(self.frame)
#Create Source
self.source = vtk.vtkCylinderSource()
self.source.SetCenter(0, 0, 0)
self.source.SetRadius(5.0)
#Create Mapper
self.mapper = vtk.vtkPolyDataMapper()
self.mapper.SetInputConnection(self.source.GetOutputPort())
#Create Actor
self.actor = vtk.vtkActor()
self.actor.SetMapper(self.mapper)
#Create poke matrix for cylinder
self.pMatrix = vtk.vtkMatrix4x4()
self.vl.addWidget(self.vtkWidget)
self.vl.addWidget(self.button)
self.vl.addWidget(self.label)
self.ren = vtk.vtkRenderer()
self.ren.AddActor(self.actor)
self.renWin = self.vtkWidget.GetRenderWindow()
self.renWin.AddRenderer(self.ren)
self.iren = self.vtkWidget.GetRenderWindow().GetInteractor()
#Settings
self.ren.SetBackground(0.2, 0.2, 0.2)
self.timeStep = 20 #ms
self.total_t = 0
#Inititalize Window, Interactor, Renderer, Layout
self.frame.setLayout(self.vl)
self.setCentralWidget(self.frame)
self.ren.ResetCamera()
self.show()
self.iren.Initialize()
# Create Timer
self.timer = QtCore.QTimer()
self.timer.timeout.connect(self.timerCallback)
self.timer.start(self.timeStep)
def timerCallback(self, *args):
self.total_t += self.timeStep / 1000
#Rotate Cylinder
angle = 2 * np.pi * self.total_t
rotMatrix = np.array([[np.cos(angle), -np.sin(angle), 0],
[np.sin(angle), np.cos(angle), 0],
[0, 0, 1]])
for i in range(3):
for j in range(3):
self.pMatrix.SetElement(i, j, rotMatrix[i, j])
self.actor.PokeMatrix(self.pMatrix)
self.ren.Render()
if __name__ == "__main__":
app = Qt.QApplication(sys.argv)
window = mainWindow()
sys.exit(app.exec_())

Answer 1

After reading the paintEvent()-Method of this file, I managed to find out, that one needs to call the Render()-Method of the Interactor-object. So instead of self.ren.Render() one needs to call self.iren.Render(). Then everything works.
Complete example code:
import sys
import vtk
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5 import Qt
import numpy as np
from vtk.qt.QVTKRenderWindowInteractor import QVTKRenderWindowInteractor
class mainWindow(Qt.QMainWindow):
def __init__(self, parent = None):
Qt.QMainWindow.__init__(self, parent)
self.frame = Qt.QFrame()
self.vl = Qt.QVBoxLayout()
self.button = QtWidgets.QPushButton("TestButton")
self.label = QtWidgets.QLabel("This is a label")
self.vtkWidget = QVTKRenderWindowInteractor(self.frame)
#Create Source
self.source = vtk.vtkCylinderSource()
self.source.SetCenter(0, 0, 0)
self.source.SetRadius(5.0)
#Create Mapper
self.mapper = vtk.vtkPolyDataMapper()
self.mapper.SetInputConnection(self.source.GetOutputPort())
#Create Actor
self.actor = vtk.vtkActor()
self.actor.SetMapper(self.mapper)
#Create poke matrix for cylinder
self.pMatrix = vtk.vtkMatrix4x4()
self.vl.addWidget(self.vtkWidget)
self.vl.addWidget(self.button)
self.vl.addWidget(self.label)
self.ren = vtk.vtkRenderer()
self.ren.AddActor(self.actor)
self.renWin = self.vtkWidget.GetRenderWindow()
self.renWin.AddRenderer(self.ren)
self.iren = self.vtkWidget.GetRenderWindow().GetInteractor()
#Settings
self.ren.SetBackground(0.2, 0.2, 0.2)
self.timeStep = 20 #ms
self.total_t = 0
#Inititalize Window, Interactor, Renderer, Layout
self.frame.setLayout(self.vl)
self.setCentralWidget(self.frame)
self.ren.ResetCamera()
self.show()
self.iren.Initialize()
# Create Timer
self.timer = QtCore.QTimer()
self.timer.timeout.connect(self.timerCallback)
self.timer.start(self.timeStep)
def timerCallback(self, *args):
self.total_t += self.timeStep / 1000
#Rotate Cylinder
angle = 2 * np.pi * self.total_t
rotMatrix = np.array([[np.cos(angle), -np.sin(angle), 0],
[np.sin(angle), np.cos(angle), 0],
[0, 0, 1]])
for i in range(3):
for j in range(3):
self.pMatrix.SetElement(i, j, rotMatrix[i, j])
self.actor.PokeMatrix(self.pMatrix)
self.iren.Render() #NOT: self.ren.Render()
if __name__ == "__main__":
app = Qt.QApplication(sys.argv)
window = mainWindow()
sys.exit(app.exec_())

Answer 2

Thanks #cakelover, I was facing same issue but in C++, your solution helped me resolve it:
//PCLVisualizer pointer
pcl::visualization::PCLVisualizer::Ptr viewer_3D;
//Renderer method to update the visualizer
viewer_3D->getRenderWindow()->GetInteractor()->Render();