[PYTHON] When you want to save the result of the callback function somewhere

Problems encountered when creating a Tkinter GUI app How can I save the processing result of the callback function called by the bind method? (= User operation such as mouse triggers as an event and calls a callback function)

The procedure is as follows:

  1. Define a class that saves the processing result in the form of an instance variable
  2. Create one object based on the class defined in step 1.
  3. Pass the class object from step 2 to the callback function when calling the bind method
  4. Set the processing result for the class object of the argument passed in the callback function

In the sample code below, after the Tkinter GUI window is displayed, The bind method calls a callback function called b1Pressed each time the left mouse button is clicked. In addition to the event (e) itself, specify a class object called obj1 as an argument passed to b1Pressed in the form of a lambda function. b1Pressed adds 1 to obj1.var_hoge each time it is called and saves the processing result in obj1.var_hoge


import tkinter as tk
from tkinter import ttk
import PIL
from PIL import Image,ImageTk

root = tk.Tk()

#Loading images
img = PIL.Image.open(r"C:\Users\User\Desktop\experiment\a.png ")
im = PIL.ImageTk.PhotoImage(img)

#Mouse click event handler
def b1Pressed(e, obj1):
        print("b1Pressed has been called!")
        obj1.var_hoge += 1
        print("var_hoge"+ str(obj1.var_hoge))
#Class for storing the processing result of the variable performed by the callback function
class storeVar():
    def __init__(self):
        self.var_hoge = 0

#Canvas settings
cvs = tk.Canvas(bg="black", width=796, height=816)
cvs.place(x=0, y=0)
cvs.create_image(0,0,image=im, anchor=tk.NW)

#Prepare a class object
obj1 = storeVar()

#Call the event handler when the mouse button is pressed
cvs.bind("<ButtonPress-1>", lambda event, arg=obj1:b1Pressed(event, arg))

The processing result is as follows (result of clicking the left mouse button four times)

guiTest.Execution result of py

b1Pressed has been called!
var_hoge is 1!
b1Pressed has been called!
var_hoge is 2!
b1Pressed has been called!
var_hoge is 3!
b1Pressed has been called!
var_hoge is 4!

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