Update frame on tab switch in ttk.Notebook

Question

I have a custom Frame with an update method that I want to call every time the user switches tab in a notebook using python2.7 ttk .

My first thought was to intercept some "tab switch event", get the frame from the event and call the update method. However, googling this yields no good results. I can't seem to catch the event, nor get the frame from a "tab click event" in a good way. My current solution below works okay but I'm looking for a better alternative. (Also with my real update method I get some nasty alloc errors).

import ttk
import Tkinter as tk

class MyFrame(ttk.Frame):
    def __init__(self, master, name):
        ttk.Frame.__init__(self, master)
        self.name = name
        self.pack()

    def update(self):
        # Update the contents of the frame...
        print "Updating %s" % self.name

class App():
    def __init__(self):
        root = tk.Tk()

        nb = ttk.Notebook(root)

        f1_name = "Tab1"
        f2_name = "Tab2"
        f1 = MyFrame(nb, f1_name)
        f2 = MyFrame(nb, f2_name)

        nb.add(f1, text=f1_name)
        nb.add(f2, text=f2_name)

        def tab_switch(event):
            if event.widget.identify(event.x, event.y) == "label":
                index = event.widget.index("@%d,%d" % (event.x, event.y))
                title = event.widget.tab(index, "text")

                if title == f1_name:
                    f1.update()
                elif title == f2_name:
                    f2.update()
                # and so on...

        nb.bind("<Button-1>", tab_switch)
        nb.pack(fill="both", expand=True)

        f1.update()  # Initial update of first displayed tab

        root.geometry("200x200")
        root.mainloop()

App()

As you can imagine this becomes very non-DRY as the amount of tabs increases...

Answer 1

You can bind to the <Visibility> or <Map> event of the frame. For example:

class MyFrame(ttk.Frame):
    def __init__(self, master, name):
        ttk.Frame.__init__(self, master)
        self.name = name
        self.pack()
        self.bind("<Visibility>", self.on_visibility)

    def on_visibility(self, event):
        self.update()

Answer 2

Instead of

def tab_switch():
    # see question...

nb.bind("<Button-1>", tab_switch)

you can do the following trick

b.bind("<<NotebookTabChanged>>", 
       lambda event: event.widget.winfo_children()[event.widget.index("current")].update())

This also removes the need to call

f1.update()  # Initial update of first displayed tab

However, the solution proposed by @BryanOakley might work better when you have different types of frames where you cannot be sure if an .update() method exists.