run daemons only when frames are opened in tkinter

Question

I have created 3 frames and each of these frame has their own daemons,to navigate among frames I am using the stack method.everything works fine but my problem is all daemons are running even though I did not open their respective frames,I know that I am loading the frames into stack that is reason all daemons started running. But I want those daemons to run only when their frame is opened,so is there any way i can do it. Example- Mainfile.py

import tkinter as tk                # python 3
from tkinter import font  as tkfont # python 3
#import Tkinter as tk     # python 2
#import tkFont as tkfont  # python 2
from Page1 import PageOne
from Page2 import PageTwo
class SampleApp(tk.Tk):

    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)

        self.title_font = tkfont.Font(family='Helvetica', size=18, weight="bold", slant="italic")

        # the container is where we'll stack a bunch of frames
        # on top of each other, then the one we want visible
        # will be raised above the others
        container = tk.Frame(self)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in (StartPage, PageOne, PageTwo):
            page_name = F.__name__
            frame = F(parent=container, controller=self)
            self.frames[page_name] = frame

            # put all of the pages in the same location;
            # the one on the top of the stacking order
            # will be the one that is visible.
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame("StartPage")

    def show_frame(self, page_name):
        '''Show a frame for the given page name'''
        frame = self.frames[page_name]
        frame.tkraise()


class StartPage(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is the start page", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)

        button1 = tk.Button(self, text="Go to Page One",
                            command=lambda: controller.show_frame("PageOne"))
        button2 = tk.Button(self, text="Go to Page Two",
                            command=lambda: controller.show_frame("PageTwo"))
        button1.pack()
        button2.pack()

if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()

the above file is a main file now in that file I am importing two more frames which are having their own daemons, file-Page1

import threading
import tkinter as tk
class PageOne(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 1", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack() 
        thread1 = threading.Thread(target=self.func)
        thread1.daemon=True
        thread1.start()
      
    def func(self):
        print("this is thread1")

file-Page2

import threading
import tkinter as tk
class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 2", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack()
        thread2 = threading.Thread(target=self.func)
        thread2.daemon=True
        thread2.start()
      
    def func(self):
        print("this is thread2")

After I run the whole program I can see both the daemons giving answers,but I want them to run only after their frame is opened,for example when frame PageOne is opened then its thread-threa1 should run the print the answer.

Is there anyway I can do that?

Note:this is just a simple example I am giving,but in real I am dealing with real-time hardware values,so by using threads and daemons,I can generate both UI and Processing stuff of hardware parallelly

You can put the starting of thread code inside a function and call this function when the page is raised. You also need to check whether the thread is already started, otherwise multiple threads of same task will be running. — acw1668, Jul 16 '20 at 07:48
Yes @acw1668 that's a good suggestion and it worked,Thank you — krishna, Jul 16 '20 at 08:02

score 0 · Accepted Answer · answered Jul 16 '20 at 14:38

The simple solution is to not create the frames until you need them. You can do that my modifying show_frame to create the frames on demand.

First, you need to modify the code that initializes the UI to not create the frames. Instead, it can just create a mapping from a page name to the page class. You need to remove the loop that begins with for F in (StartPage, PageOne, PageTwo): and replace it with something like this:

self.frames = {
    "StartPage": StartPage, 
    "PageOne": PageOne, 
    "PageTwo": PageTwo,
}

Next, modify show_frame to destroy any existing frame and then create the new frame. It should look something like this:

def show_frame(self, page_name):
    # destroy the old frame
    for child in container.winfo_children():
        child.destroy()

    # create the new frame
    frame_class = self.frames[page_name]
    frame = frame_class(parent=self.container, controller=self)
    frame.pack(fill="both", expand=True)

Another solution would be to keep the original code, but only start the threads when the frame is shown. An example of how to run a function when the frame is shown can be seen in the accepted answer to this question: How would I make a method which is run every time a frame is shown in tkinter

Thank you @Bryan Oakley this is the best thing – krishna Jul 16 '20 at 14:49 — krishna, Jul 16 '20 at 14:49

run daemons only when frames are opened in tkinter

1 Answers1