Problem using qt5agg in python matplotlib: Window not displaying anything

Question

I want to display charts using matplotlib's qt5agg backend. The tutorial's code runs fine:

import sys
import numpy as np
from matplotlib.backends.qt_compat import QtCore, QtWidgets
from matplotlib.backends.backend_qt5agg import (
    FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
from matplotlib.figure import Figure


class ApplicationWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self._main = QtWidgets.QWidget()
        self.setCentralWidget(self._main)
        layout = QtWidgets.QVBoxLayout(self._main)
        static_canvas = FigureCanvas(Figure(figsize=(5, 3)))
        layout.addWidget(static_canvas)
        self._static_ax = static_canvas.figure.subplots()
        t = np.linspace(0, 10, 501)
        self._static_ax.plot(t, np.tan(t), ".")


if __name__ == "__main__":
    qapp = QtWidgets.QApplication(sys.argv)
    app = ApplicationWindow()
    app.show()
    qapp.exec_()

It shows a perfect chart. But the code I've written looks similar, fails to run: no exeption was raised, but no chart showed. Just a blank window. Here's my code:

import numpy
from matplotlib.pyplot import Figure
from matplotlib.backends.backend_qt5agg import (
        FigureCanvas, NavigationToolbar2QT as NavigationToolbar)
from matplotlib.backends.qt_compat import QtWidgets, QtGui
import sys

class MyWindow(QtWidgets.QWidget):
        def __init__(self):
                super().__init__()
                self.grid = QtWidgets.QGridLayout()
                self.canvas = FigureCanvas(Figure(figsize=(3, 2)))
                self.grid.addWidget(self.canvas, 0, 0)
                self.canvas_fig = self.canvas.figure.subplots()
                self.canvas_fig.plot([1, 2, 3, 4, 5], [0., 1., 2., 3., 4.])

if __name__ == "__main__":
    qapp = QtWidgets.QApplication()
    app = MyWindow()
    app.show()
    qapp.exec_()

It runs like this: What's wrong with this code? How to run it successfully?

Can anyone help me?