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PyQtGraph – X Change Signal for Bar Graph

  • Last Updated : 25 Sep, 2020

In this article we will see how we can get the x-change signal for the bar graph in the PyQtGraph module. PyQtGraph is a graphics and user interface library for Python that provides functionality commonly required in designing and science applications. Its primary goals are to provide fast, interactive graphics for displaying data (plots, video, etc.) and second is to provide tools to aid in rapid application development (for example, property trees such as used in Qt Designer).A bar chart or bar graph is a chart or graph that presents categorical data with rectangular bars with heights or lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is sometimes called a column chart. X change signal is emitted when the X value of the bar graph is changed by default it is 0.

We can create a plot window and bar graph with the help of commands given below

# creating a pyqtgraph plot window
window = pg.plot()

# creating a bar graph of green color
bargraph = pg.BarGraphItem(x=x, height=y1, width=0.6, brush='g')

In order to do this we use xChanged.connect method with the bar graph object

Syntax : bargraph.xChanged.connect(method)

Argument : It takes method as argument



Return : It returns None

Below is the implementation




# importing Qt widgets
from PyQt5.QtWidgets import * import sys
  
# importing pyqtgraph as pg
import pyqtgraph as pg
from PyQt5.QtGui import *
  
# Bar Graph class
class BarGraphItem(pg.BarGraphItem):
  
    # constructor which inherit original
    # BarGraphItem
    def __init__(self, *args, **kwargs):
        pg.BarGraphItem.__init__(self, *args, **kwargs)
  
    # creating a mouse double click event
    def mouseDoubleClickEvent(self, e):
  
        # setting X value (from origin)
        self.setX(200)
  
  
  
class Window(QMainWindow):
  
    def __init__(self):
        super().__init__()
  
        # setting title
        self.setWindowTitle("PyQtGraph")
  
        # setting geometry
        self.setGeometry(100, 100, 600, 500)
  
  
        # icon
        icon = QIcon("skin.png")
  
        # setting icon to the window
        self.setWindowIcon(icon)
  
        # calling method
        self.UiComponents()
  
        # showing all the widgets
        self.show()
  
    # method for components
    def UiComponents(self):
  
        # creating a widget object
        widget = QWidget()
  
        # creating a label
        label = QLabel("Geeksforgeeks")
  
        # creating a plot window
        plot = pg.plot()
  
        # create list for y-axis
        y1 = [5, 5, 7, 10, 3, 8, 9, 1, 6, 2]
  
        # create horizontal list i.e x-axis
        x = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
        # create pyqt5graph bar graph item
        # with width = 0.6
        # with bar colors = green
        bargraph = BarGraphItem(x = x, height = y1, width = 0.6, brush ='g')
  
        # add item to plot window
        # adding bargraph item to the plot window
        plot.addItem(bargraph)
  
        # Creating a grid layout
        layout = QGridLayout()
  
        # setting this layout to the widget
        widget.setLayout(layout)
  
        # adding label in the layout
        layout.addWidget(label, 1, 0)
  
        # plot window goes on right side, spanning 3 rows
        layout.addWidget(plot, 0, 1, 3, 1)
  
        # setting this widget as central widget of the main widow
        self.setCentralWidget(widget)
  
        # signal emitted when x  is changed
        bargraph.xChanged.connect(lambda: do_action())
  
        # do action method called by bar graph
        def do_action():
  
            # setting text to the label
            label.setText("X value of bar graph is Changed")
  
  
  
  
# create pyqt5 app
App = QApplication(sys.argv)
  
# create the instance of our Window
window = Window()
  
# start the app
sys.exit(App.exec())

Output :

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