Python tkinter 文本小部件“已修改”事件似乎未正确触发

Question

I wanted to monitor when the text in a tkinter Text widget was modified so that a user could save any new data they had entered. Then on pressing 'Save' I wanted to reset this.

I bound the Text widget's <<Modified>> event to a function so that making any changes to the text would update the 'Save' button from 'disabled' to 'normal' state. After hitting the Save button I ran a function which reset the modified flag and disabled the Save button again until further changes were made.

But I found that it seemed to only fire the event once. Hitting Save didn't reset the button to a 'disabled' state, and editing the text didn't seem to affect the Save button's state either after the first time.

Below is a minimal example to show how the flag doesn't seem to be reset.

EXAMPLE

import tkinter as tk

root = tk.Tk()

def text_modified(event=None):
    status_label.config(text="Modified = True")

def reset():
    if not text_widget.edit_modified():
        return
    status_label.config(text="Modified = False")
    text_widget.edit_modified(False)

text_widget = tk.Text(root, width=30, height=5)
text_widget.pack()
text_widget.bind("<<Modified>>", text_modified)

status_label = tk.Label(root, text="Modified = False")
status_label.pack()

reset_btn = tk.Button(root, text="Reset", command=reset)
reset_btn.pack()

root.mainloop()

Answer 1

SOLUTION

It turns out that binding the <<Modified>> event to a function means that the function will run not when the Text widget text is changed, but whenever the modified flag is changed - whether it changes to True or to False . So my Save button was saving the data, disabling itself, and resetting the modified flag to False , and this flag change fired the <<Modified>> event, which was bound to a function which un-disabled the Save button again.

Here's a minimal example which shows what's going on. We just need to adjust the function we've bound the <<Modified>> event to so that it deals with modified being False as well:

import tkinter as tk

root = tk.Tk()

def modified_flag_changed(event=None):
    if text_widget.edit_modified():
        status_label.config(text="Modified = True")
        print("Text modified")
    else:
        print("Modified flag changed to False")

def reset():
    if not text_widget.edit_modified():
        print("Doesn't need resetting")
        return
    status_label.config(text="Modified = False")
    text_widget.edit_modified(False)
    print('Reset')

text_widget = tk.Text(root, width=30, height=5)
text_widget.pack()
text_widget.bind("<<Modified>>", modified_flag_changed)

status_label = tk.Label(root, text="Modified = False")
status_label.pack()

reset_btn = tk.Button(root, text="Reset", command=reset)
reset_btn.pack()

root.mainloop()