Embedding matplotlib figure in QtDesigner GUI

Question

I am trying to muddle my way through embedding a matplotlib figure inside of a Qt GUI created using Qt Designer. I am already able to create the figure I want just through Python. I've created a basic GUI with widgets to allow me to select/load input files, and plot the data in those files in a matplotlib figure that is embedded in the GUI. I accomplish this by adding a blank widget to the GUI called plotwidget, and then calling the GraphInit class with this widget as input.

The problem I am currently facing is that while my plot shows up and updates as desired inside the GUI, it doesn't seem to pay attention to the size policy defined for it in either my Python code (where the FigureCanvas is created) or for the plotWidget widget in Qt Designer. I have been using this demo, among others, as a starting point for this project. However, all of these examples have generated the GUI entirely from within Python. I suspect I am doing something wrong in assigning the matplotlib figure to the widget, but I haven't been able to figure out what.

Code (import & plotting code removed, but the core where figure is added is there):

import sys
import os
import matplotlib
matplotlib.use('Qt5Agg')
from PyQt5 import QtCore, QtGui
from PyQt5.QtWidgets import QApplication, QMessageBox, QFileDialog, QPushButton, QLabel, QRadioButton, QDoubleSpinBox, QSpinBox, QWidget, QSizePolicy, QMainWindow
import PyQt5.uic

from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure

import json
from datetime import datetime
import numpy as np


class LogViewer(QApplication):
    def __init__(self):
        QApplication.__init__(self, sys.argv)
        self.ui = UI()

    @staticmethod
    def main():
        vwr = LogViewer()
        vwr.run()

    def run(self):
        self.ui.win.show()  # Show the UI
        self.ui.run()  # Execute the UI run script
        self.exec_()


class Graph_init(FigureCanvas):

    def __init__(self, parent=None):

        fig = Figure()
        self.axes = fig.add_subplot(111)
        self.compute_initial_figure()
        self.axes.grid()

        FigureCanvas.__init__(self, fig)
        self.setParent(parent)

        FigureCanvas.setSizePolicy(self, QSizePolicy.Expanding, QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)

    def compute_initial_figure(self):
        pass

class UI(object):
    def __init__(self):
        ui_path = os.path.dirname(os.path.realpath(__file__))
        self.win = PyQt5.uic.loadUi(ui_path + '\\logview.ui')
        self.filename = ui_path + '\\test.txt'
        self.plotWin = Graph_init(self.win.plotWidget)

    def run(self):
        self.init_ui()  # get initial values from the controllers
        self.attach_ui_connections()

    def init_ui(self):
        w = self.win
        w.txtLogFilename.setText(self.filename.split('/')[-1])  # just the file (no path)

    def attach_ui_connections(self):
        w = self.win



if __name__ == '__main__':
    LogViewer.main()

GUI is available here. Any suggestions appreciated!

Answer 1

I checked your ui file and plotWidget has no layout at all. Try to give it one, I suggest a grid layout.

Then, after parenting the canvas

self.setParent(parent)

try adding it to the parent layout:

parent.layout().addWidget(self)