Embedd instance of Matplotlib canvas in pyqt - plot not showing up

Question

I tried to keep the example as short as possible. There is a similar question on SO. In contrast to the answer provided in the mentioned question, I would like to define a MatplotlibFigure class so that I can reuse the code. I added a reference to the instance of Figure as self.figure = MatplotlibFigure() in the function make_tab1 and added self.figure to the splitter. The pushbutton seems to work because I can save the figure using the navigation toolbar. However, the axis are not shown in the GUI.

Why are the axis not visible ?

import sys
from PyQt5.QtWidgets import QMainWindow, QApplication, QPushButton, QWidget, QAction, QTabWidget, QVBoxLayout,\
                            QHBoxLayout, QGridLayout, QSplitter, QFrame, QTextEdit, QFileDialog, QGroupBox,\
                            QButtonGroup, QLabel, QRadioButton

from PyQt5 import QtCore

import matplotlib
from matplotlib import figure
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar

class MatplotlibFigure(QWidget):

    # constructor
    def __init__(self):
        super().__init__()
        #self.layout = QBoxLayout()
        self.figure = matplotlib.figure.Figure()
        self.canvas = FigureCanvas(self.figure)
        self.toolbar = NavigationToolbar(self.canvas, self)
        #self.layout.addWidget(self.canvas)

    def plot(self):
        self.figure.clf()
        ax = self.figure.add_subplot(111)
        x = [i for i in range(100)]
        y = [i**0.5 for i in x]
        ax.plot(x, y, 'g*-')
        self.canvas.draw_idle()
        print('PLOTTED')


class MainApp(QMainWindow):
    """ This creates the main Window and configures its look
    """
    def __init__(self):
        '''
        Initializes the class with standard parameters
        '''
        super().__init__()
        self.title = 'Data Analysis App'

        # start at top left corner of the screen
        self.left = 0
        self.top = 0

        # set the window height and width
        self.width = 1280
        self.height = 780

        # set the styles of fonts etc.
        self.setStyleSheet('font-size: 16pt')

        # call the makeUI method
        self.makeUI()

    def makeUI(self):
        # set window geometry
        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)

        # generate the tab layout
        self.table_widget = MyTableWidget()
        self.setCentralWidget(self.table_widget)

        # apparently we have to call the show method in order to show it
        self.show()


class MyTableWidget(QWidget):
    """
    Initializes the tab layout
    """

    def __init__(self):
        super().__init__()
        self.layout = QVBoxLayout(self)

        # initialize the tab screens
        self.tabs = QTabWidget()

        # add the tab screens to the tab widget
        self.tabs.resize(600, 600)

        # make the layout of the tabs
        self.make_tab1()

        # initialize the tabs
        self.layout.addWidget(self.tabs)
        self.setLayout(self.layout)

    def make_tab1(self):
        """Style of tab 1 is created here"""

        '''Defines master layout of tab1'''
        tab1 = QWidget()
        tab1.layout = QHBoxLayout()

        '''Button Section'''

        # converts the data into excel and pandas dataframe
        btn_plot_data = QPushButton('Plot data')
        btn_plot_data.clicked.connect(self.plot_data)


        '''Button layout section'''
        btn_layout = QVBoxLayout()
        btn_layout.addWidget(btn_plot_data)
        btn_layout.addStretch(1)

        '''Page layout section '''

        left = QFrame()
        left.setLayout(btn_layout)

        self.figure = MatplotlibFigure()

        # combine the buttons and the canvas in a splitter layout
        splitter1 = QSplitter(QtCore.Qt.Horizontal)
        splitter1.addWidget(left)
        splitter1.addWidget(self.figure)
        splitter1.setSizes([5, 400])


        # add the last splitter to the layout
        tab1.layout.addWidget(splitter1)
        tab1.setLayout(tab1.layout)
        self.tabs.addTab(tab1, 'Get Data Module')

    ''' Methods section
    '''
    def plot_data(self):
        self.figure.plot()


if __name__ == '__main__':
    """ This code block is always the same and makes sure that e.g. STRG+C kills the window etc.
    """
    app = QApplication(sys.argv)
    ex = MainApp()
    sys.exit(app.exec())

erocoar · Accepted Answer · 2017-12-02 19:58:47Z

2

You forgot to set a layout for your MatplotlibFigure class (remember that it is a QWidget in your case, not a canvas)

def __init__(self):
    super().__init__()
    #self.layout = QBoxLayout()
    self.figure = matplotlib.figure.Figure()
    self.canvas = FigureCanvas(self.figure)
    self.toolbar = NavigationToolbar(self.canvas, self)

    layout = QVBoxLayout(self)
    layout.addWidget(self.toolbar)
    layout.addWidget(self.canvas)

answered Dec 2, 2017 at 19:58

erocoar

5,9333 gold badges26 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Moritz Over a year ago

What I do not understand: I create a layout inside that class and add the widgets to it. So far so good. Then I pass the instance of the class (a QWidget) to the splitter. How does the splitter now about the layout ?

Moritz Over a year ago

I accepted your answer because this solution has the effect, that the plot automatically resizex if I change the window size

erocoar Over a year ago

The splitter is just a container for all the widgets you add to it -- each with its own layout, its own child widgets, etc. For example, add print(splitter1.children()) to make_tab1

eyllanesc · Accepted Answer · 2017-12-02 19:54:45Z

2

You need to set a parent to FigureCanvas:

self.canvas.setParent(self)

answered Dec 2, 2017 at 19:54

eyllanesc

246k19 gold badges205 silver badges282 bronze badges

2 Comments

Moritz Over a year ago

Is this a generic approach or is this solution matplotlib specific ? Or in other words: Is this is a pattern which occurs in general during OO programming ?

eyllanesc Over a year ago

This is a Qt rule, a widget is drawn in the parent widget in the default position (0, 0) (unless it is the parent widget), or you place it through a layout as the other solution shows.

Collectives™ on Stack Overflow

Embedd instance of Matplotlib canvas in pyqt - plot not showing up

2 Answers 2

3 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related