How to limit the number of events generated by widget

Question

I\'m using a spinbox to control the size of fonts in real time, for a zooming effect. A spinbox widget can generate a lot of events. As long as you hold down a direction key

Answer 1

I used similar solutions for both kinds of spinboxes but the implementation is a bit different since they don't use the same events. The idea is to create a Spinbox class with an _increment_lock attribute which is set to True when the Spinbox is incremented and after a delay is set back to False. Then, the events that increment the spinbox are bound to a method that checks _increment_lock before actually performing the increment. The principle is the same for the decrement.

For the tk.Spinbox, I used the bindings to the <Up> and <Down> arrows to implement the above solution while I used the bindings to <<Increment>> and <<Decrement>>.

Here is the code:

import tkinter as tk
import tkinter.ttk as ttk


class MySpinbox(tk.Spinbox):
    def __init__(self, master=None, delay=500, **kwargs):
        kwargs.setdefault('repeatdelay', delay)
        kwargs.setdefault('repeatinterval', delay)
        tk.Spinbox.__init__(self, master, **kwargs)
        self.delay = delay  # repeatdelay in ms
        self.bind('<Up>', self._on_increment)
        self.bind('<Down>', self._on_decrement)
        self._increment_lock = False
        self._decrement_lock = False

    def _unlock_increment(self):
        self._increment_lock = False

    def _on_increment(self, event):
        if self._increment_lock:
            return "break"  # stop the increment
        else:
            self._increment_lock = True
            self.after(self.delay, self._unlock_increment)

    def _unlock_decrement(self):
        self._decrement_lock = False

    def _on_decrement(self, event):
        if self._decrement_lock:
            return "break"  # stop the increment
        else:
            self._decrement_lock = True
            self.after(self.delay, self._unlock_decrement)


class MyTtkSpinbox(ttk.Spinbox):
    def __init__(self, master=None, delay=500, **kwargs):
        ttk.Spinbox.__init__(self, master, **kwargs)
        self.delay = delay  # repeatdelay in ms
        self.bind('<<Increment>>', self._on_increment)
        self.bind('<<Decrement>>', self._on_decrement)
        self._increment_lock = False
        self._decrement_lock = False

    def _unlock_increment(self):
        self._increment_lock = False

    def _on_increment(self, event):
        if self._increment_lock:
            return "break"  # stop the increment
        else:
            # generate a virtual event corresponding to when the spinbox
            # is actually incremented
            self.event_generate('<<ActualIncrement>>')
            self._increment_lock = True
            self.after(self.delay, self._unlock_increment)

    def _unlock_decrement(self):
        self._decrement_lock = False

    def _on_decrement(self, event):
        if self._decrement_lock:
            return "break"  # stop the increment
        else:
            # generate a virtual event corresponding to when the spinbox
            # is actually decremented
            self.event_generate('<<ActualDecrement>>')
            self._decrement_lock = True
            self.after(self.delay, self._unlock_decrement)


class App(tk.Tk):
    def __init__(self):
        super().__init__()
        self.rowconfigure(990, weight=1)
        self.columnconfigure(0, weight=1)
        self.title('Timed Events Demo')
        self.geometry('420x200+20+20')

        tk_spn1 = MySpinbox(self, value=0, values=list(range(0, 1000)))
        tk_spn1.grid(row=0, pady=5)

        tk_spn2 = MyTtkSpinbox(self, from_=0, to=1000)
        tk_spn2.grid(row=1, pady=5)

        def test(e):
            print(e)

        tk_spn2.bind('<<ActualIncrement>>', test)


if __name__ == '__main__':
    app = App()
    app.mainloop()