How to delete old plot on Matplotlib figure embedded in PyQt5? - matplotlib

Question

I am using matplotlib figure embedded in pyqt5 to draw a frame taking the height and the width from line edit entries.It works well but when I change the values inside the line edits and click on the push button it will draw another frame over the previous one. I have tried plt.gcf().clear() and ax.clear and they did not work.
class Window(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle("Draw Frame")
self.setGeometry(100,100,680, 450)
# Creation of figure and canvas
self.figure = plt.figure()
self.canvas = FigureCanvas(self.figure)
self.ax = self.figure.add_subplot(111)
self.ax.axis("off")
#self.toolbar = NavigationToolbar(self.canvas, self)
self.plot_widget = QWidget(self)
self.plot_widget.setGeometry(250, 10, 400, 400)
plot_box = QVBoxLayout()
plot_box.addWidget(self.canvas)
self.plot_widget.setLayout(plot_box)
self.label1=QLabel("Frame height",self)
self.label1.move(10,30)
self.label2 = QLabel("Frame height", self)
self.label2.move(10, 70)
self.lineEdit1=QLineEdit(self)
self.lineEdit1.move(100,30)
self.lineEdit1.setText("10")
self.lineEdit2 = QLineEdit(self)
self.lineEdit2.move(100, 70)
self.lineEdit2.setText("20")
self.button = QPushButton('Draw Frame', self)
self.button.clicked.connect(self.plot)
self.button.move(70, 350)
self.show()
def plot(self):
if len(self.lineEdit1.text())!=0:
self.h=int(self.lineEdit1.text())
else:
self.h=0
if len(self.lineEdit2.text()) != 0:
self.w=int(self.lineEdit2.text())
else:
self.w=0
x = [0, 0, self.w, self.w]
y = [0, self.h, self.h, 0]
self.ax.plot(x, y)
self.canvas.draw()
Picture of the app

Answer 1

Instead of clearing the axes you may update the line that is drawn with the new coordinates.
from PyQt5.QtWidgets import *
import matplotlib.pyplot as plt
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
import sys
class Window(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle("Draw Frame")
self.setGeometry(100,100,680, 450)
# Creation of figure and canvas
self.figure = plt.figure()
self.canvas = FigureCanvas(self.figure)
self.ax = self.figure.add_subplot(111)
self.ax.axis("off")
self.line, = self.ax.plot([])
self.ax.axis([0,100,0,100])
#self.toolbar = NavigationToolbar(self.canvas, self)
self.plot_widget = QWidget(self)
self.plot_widget.setGeometry(250, 10, 400, 400)
plot_box = QVBoxLayout()
plot_box.addWidget(self.canvas)
self.plot_widget.setLayout(plot_box)
self.label1=QLabel("Frame height",self)
self.label1.move(10,30)
self.label2 = QLabel("Frame height", self)
self.label2.move(10, 70)
self.lineEdit1=QLineEdit(self)
self.lineEdit1.move(100,30)
self.lineEdit1.setText("10")
self.lineEdit2 = QLineEdit(self)
self.lineEdit2.move(100, 70)
self.lineEdit2.setText("20")
self.button = QPushButton('Draw Frame', self)
self.button.clicked.connect(self.plot)
self.button.move(70, 350)
self.show()
def plot(self):
if len(self.lineEdit1.text())!=0:
self.h=int(self.lineEdit1.text())
else:
self.h=0
if len(self.lineEdit2.text()) != 0:
self.w=int(self.lineEdit2.text())
else:
self.w=0
x = [0, 0, self.w, self.w]
y = [0, self.h, self.h, 0]
self.line.set_data(x,y)
self.canvas.draw()
if __name__=='__main__':
app = QApplication(sys.argv)
w = Window()
app.exec_()

Answer 2

As mentioned in the comment above, you need to call self.ax.clear() every time you click the button. Otherwise you will be redrawing on the same plot. Not sure why your graph doesnt reset on clear(), but here is the code I ran which worked fine. Let me know if it works for you:
from PyQt5.QtWidgets import *
import matplotlib.pyplot as plt
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
import sys
class Window(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle("Draw Frame")
self.setGeometry(100,100,680, 450)
# Creation of figure and canvas
self.figure = plt.figure()
self.canvas = FigureCanvas(self.figure)
self.ax = self.figure.add_subplot(111)
self.ax.axis("off")
#self.toolbar = NavigationToolbar(self.canvas, self)
self.plot_widget = QWidget(self)
self.plot_widget.setGeometry(250, 10, 400, 400)
plot_box = QVBoxLayout()
plot_box.addWidget(self.canvas)
self.plot_widget.setLayout(plot_box)
self.label1=QLabel("Frame height",self)
self.label1.move(10,30)
self.label2 = QLabel("Frame height", self)
self.label2.move(10, 70)
self.lineEdit1=QLineEdit(self)
self.lineEdit1.move(100,30)
self.lineEdit1.setText("10")
self.lineEdit2 = QLineEdit(self)
self.lineEdit2.move(100, 70)
self.lineEdit2.setText("20")
self.button = QPushButton('Draw Frame', self)
self.button.clicked.connect(self.plot)
self.button.move(70, 350)
self.show()
def plot(self):
self.ax.clear()
if len(self.lineEdit1.text())!=0:
self.h=int(self.lineEdit1.text())
else:
self.h=0
if len(self.lineEdit2.text()) != 0:
self.w=int(self.lineEdit2.text())
else:
self.w=0
x = [0, 0, self.w, self.w]
y = [0, self.h, self.h, 0]
self.ax.plot(x, y)
self.canvas.draw()
if __name__=='__main__':
app = QApplication(sys.argv)
w = Window()
app.exec_()