Dfyjkt

In this post I asked how to embed a matplotlib plot in a pyqt5 gui which is working fine now. Now I have a further problem that I couldn't solve until now: how can I update the figure?

I tried to update the canvas by calling

self.plotWidget = FigureCanvas(fig)

every time with a new "fig" object but nothing happened. So I tried to add it to the layout

self.lay.addWidget(self.plotWidget)

but this adds another subplot to the widget. I guess that I have to clear the previous plot before updating but I don't know how to do it.

What is the correct strategy to replot using the update method?

Thanks!

# -*- coding: utf-8 -*-

import sys
import numpy as np 

from PyQt5 import QtCore, QtWidgets, uic

import matplotlib
matplotlib.use('QT5Agg')

import matplotlib.pylab as plt

from matplotlib.backends.qt_compat import QtCore, QtWidgets, is_pyqt5
from matplotlib.backends.backend_qt5agg import FigureCanvas, NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure

class MyWindow(QMainWindow):

 def __init__(self):

 super(MyWindow, self).__init__()
 uic.loadUi('test.ui', self) 

 # test data
 data = np.array([0.7,0.7,0.7,0.8,0.9,0.9,1.5,1.5,1.5,1.5]) 
 fig, ax1 = plt.subplots()
 bins = np.arange(0.6, 1.62, 0.02)
 n1, bins1, patches1 = ax1.hist(data, bins, alpha=0.6, density=False, cumulative=False)

 # plot
 self.plotWidget = FigureCanvas(fig)
 self.lay = QtWidgets.QVBoxLayout(self.content_plot) 
 self.lay.setContentsMargins(0, 0, 0, 0) 
 self.lay.addWidget(self.plotWidget)

 # add toolbar
 self.addToolBar(QtCore.Qt.BottomToolBarArea, NavigationToolbar(self.plotWidget, self)) 

 # button event
 self.pushButton.clicked.connect(self.update)

 # show window
 self.show() 

 #########################################

 def update(self):

 data = np.array([0.1,0.1,0.1,0.1,0.3,0.3,1.7,1.7,1.7,1.7]) 
 fig, ax1 = plt.subplots()
 bins = np.arange(0.6, 1.62, 0.02)
 n1, bins1, patches1 = ax1.hist(data, bins, alpha=0.6, density=False, cumulative=False)

 # show plot in canvas 
 self.plotWidget = FigureCanvas(fig)
 self.toolbarWidget = NavigationToolbar(self.plotWidget, self) 


if __name__ == '__main__':

 app = QtWidgets.QApplication(sys.argv)
 window = MyWindow()
 sys.exit(app.exec_())

You should not create a new figure, instead, reuse the axes that you already have. That means that you have to keep a reference to that object first.

I cannot test the code right now, but you should do something like

def __init__(self):
 (...)
 self.fig, self.ax = plt.subplots()
 (...)

def update(self):
 data = (...)
 self.ax.cla() # clear the axes content
 self.ax.hist(...)
 self.fig.canvas.draw_idle() # actually draw the new content