Question

This is a followup question from this one. Connecting Pyside with matplotlib

My PythonFu is failing me to do a simple thing: design a GUI using QtDesigner, convert it, and do a QPushButton to draw something. It works when QtDesigner is not being used, but QtDesigner will be needed as the application grows more complex, so it must be used. Here is the code:

** main.py **

    import sys
import platform

import numpy as np
import PySide
from PySide import QtCore
from PySide.QtGui import QApplication, QMainWindow, QTextEdit,\
                         QPushButton,  QMessageBox, QWidget, QVBoxLayout





__version__ = '0.0.1'

from mpl import Ui_MainWindow

class MainWindow(QMainWindow, Ui_MainWindow):


    def __init__(self, parent=None):

        super(MainWindow, self).__init__(parent)

        self.main_frame = Ui_MainWindow()
        self.main_frame.setupUi(self)

        #self.button = QPushButton('Run')
    def plot_stuff(self):

        x = np.arange(1024)
        self.main_frame.widget.axes.plot(np.exp(-x / 256) * np.cos(2 * np.pi * x / 32), 'g')
        self.main_frame.widget.canvas.draw()




if __name__ == '__main__':
    app = QApplication(sys.argv)
    frame = MainWindow()

    frame.main_frame.pushButton.clicked.connect(frame.plot_stuff)

    frame.show()
    app.exec_()

** matplotlibwidget.py **

import matplotlib

matplotlib.use('Qt4Agg')
matplotlib.rcParams['backend.qt4']='PySide'


from matplotlib.figure import Figure
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas



class MatplotlibWidget(FigureCanvas):

    def __init__(self, parent=None):
        super(MatplotlibWidget, self).__init__(Figure())

        self.setParent(parent)
        self.figure = Figure()
        self.canvas = FigureCanvas(self.figure)
        self.axes = self.figure.add_subplot(111)

and ** mpl.py **, converted from mpl.ui

from PySide import QtCore, QtGui

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(640, 480)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(20, 410, 74, 20))
        self.pushButton.setObjectName("pushButton")
        self.widget = MatplotlibWidget(self.centralwidget)
        self.widget.setGeometry(QtCore.QRect(100, 40, 471, 321))
        self.widget.setObjectName("widget")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 640, 17))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.pushButton.setText(QtGui.QApplication.translate("MainWindow", "Run", None, QtGui.QApplication.UnicodeUTF8))

from widgets.matplotlibwidget import MatplotlibWidget

The button connection works, but the graph is never shown.

Thanks!

Answer 1

In your main.py module replace

self.main_frame.widget.canvas.draw()

with

self.main_frame.widget.draw()

From my understanding of matplotlib you were drawing the wrong canvas. According to the docs the widget that you promoted is now your canvas and that’s the one you’re supposed to draw.