I want to plot a figure with embedded matplotlib in PyQt. I am using Qt Designer for the main window, and writing python code for the signal and slots connexion part.

So my code looks like this :

import sys
from PyQt4 import QtCore, QtGui, uic
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas 
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QT as NavigationToolbar
import matplotlib.pyplot as plt
import pandas as pd
import numpy as np


qtCreatorFile = "main.ui" # my Qt Designer file 

Ui_MainWindow, QtBaseClass = uic.loadUiType(qtCreatorFile)

class MyApp(QtGui.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        Ui_MainWindow.__init__(self)
        self.setupUi(self)

        self.figure = plt.figure()

        self.canvas = FigureCanvas(self.figure)

        self.csvbutton.clicked.connect(self.plot)

    def plot(self):

        filePath="/path to csv file here"
        df= pd.read_csv(str(filePath),index_col='date')
        df.index = pd.to_datetime(df.index, unit='s')
        ax = self.figure.add_subplot(111)
        ax.hold(False)
        ax.plot(df, '*-')
        self.canvas.draw()



if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    window = MyApp()
    window.show()
    sys.exit(app.exec_())

My main problem is the connexion between the Qt Designer file and the python code, I couldn't set a canvas widget directly in Qt Designer and I'm still struggling to find where the error lays in my code. Your help is very appreciated, thank you.

  • If you didn't set the canvas in designer than, in its current state, your self.canvas is not included in any layout of the window. Try this: in designer make a container like object in the place you want to put the canvas (QWidget, Groupbox, etc.). In the code build your canvas, add it to a local layout (QHBoxLayout for example) and make a .setLayout(canvaslayout) in your container. This should place your canvas correctly in the UI. – armatita Jul 28 '17 at 10:24
  • What error do you get? – Trilarion Aug 9 '17 at 10:19
up vote 3 down vote accepted

In order to use matplotlib in Qt Designer can not be done directly, for this we must promote a QWidget to use FigureCanvas or better a class that inherits from it as I show below, first we create a class called Canvas in file called canvas.py:

canvas.py

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas 
import matplotlib.pyplot as plt

class Canvas(FigureCanvas):
    def __init__(self, parent=None):
        self.figure = plt.figure()
        FigureCanvas.__init__(self, self.figure)
        self.setParent(parent)

After creating the design through Qt Designer, we have all the elements we want, but where we want to place the argument we use the Widget element that is in Containers, and we name it canvas:

enter image description here

Then we promote it by right click and choose the option promoted to ...:

enter image description here

Obtaining what is shown in the following image, in Promoted Class Name we place Canvas as the name of the class, and in Header File we place canvas.h (in Header File the file.py file is placed, for example package.subpackage.file.h), then press Add and after Promote:

enter image description here

At the end we get a file structure similar to the following:

.
├── canvas.py
└── main.ui

Then we create the file main.py where we place your code with small variations:

main.py

import matplotlib
matplotlib.use('Qt4Agg')

import sys
from PyQt4 import QtCore, QtGui, uic
import matplotlib.pyplot as plt
import pandas as pd
import numpy as np


qtCreatorFile = "main.ui" # my Qt Designer file 

Ui_MainWindow, QtBaseClass = uic.loadUiType(qtCreatorFile)

class MyApp(QtGui.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        Ui_MainWindow.__init__(self)
        self.setupUi(self)
        self.csvbutton.clicked.connect(self.plot)

    def plot(self):

        filePath="data.csv"
        df= pd.read_csv(str(filePath),index_col='date')
        ax = self.canvas.figure.add_subplot(111)
        ax.hold(False)
        ax.plot(df, '*-')
        self.canvas.draw()



if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    window = MyApp()
    window.show()
    sys.exit(app.exec_())

In the end we get the following:

enter image description here

You can find the complete project here


If you want to add the NavigationToolbar you can use the following code:

...
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QT as NavigationToolbar 

...

class MyApp(QtGui.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        Ui_MainWindow.__init__(self)
        self.setupUi(self)
        self.addToolBar(NavigationToolbar(self.canvas, self))
        ...

enter image description here