View.can_pop and View.on_confirm_pop

[FeodorFitsner]

Close #5280

Summary by Sourcery

Add support for customizing view navigation behavior with can_pop and on_confirm_pop properties

New Features:

• Introduce can_pop property to control whether a view can be popped
• Add on_confirm_pop event handler to provide custom pop confirmation logic

Enhancements:

• Implement platform-specific navigation handling for root and nested views
• Add method to programmatically confirm or cancel view pop navigation

[SIRGPrice]

Hi @FeodorFitsner , I updated some code to 0.28.3 this morning and this navigation changes and everything in general worked very nice.

I have a suggestion for a feature associated with the pop of the views. In android flet 0.27.6, on_view_pop was called directly when native android button pressed, making possible a view exit logic, like a confirmation back, save or exit dialog.

Now back button event pop the view first and then on_view_pop is called wich (I can be wrong) leaves no options to any logics. It could be possible to associate can_pop with other event called on_pop, for example, that gives the opportunity to page.views.pop() yourself or do other things instead?

Thank you for everything.

[FeodorFitsner]

Got it. In 0.28.3 we added a few hooks to View control that allows you to control its "popping" :) logic.
There is a new View.can_pop bool property which is True by default and allows for any view to be removed with no questions asked. However, if you set View.can_pop to False then you can add View.on_confirm_pop event handler where you can open an alert dialog ton confirm or do other checks and then call View.confirm_pop(True|False) method to either allow or prevent view from removal. In its simplest form, setting page.views[0].canPop = False for root view prevents closing app with hardware back button on Android. Let me know if you have any questions. I'm adding this to the docs.

[SIRGPrice]

I undertand, It seems I was wrong with interpretation of the new pop mechanics. I tryed the method you mention when defining the View 's:

• page x = View(can_pop=False, on_confirm_pop = lambda _: function(args))

But the can_pop = False disable the pop event so on_confirm_pop never is called and function(args) never executed.

The hardware back button dont do nothing.

This has sense for you?

Thanks.

[FeodorFitsner]

Make sure you have flet-desktop installed of 0.28.3 version (check with pip list).

I'm using this example to test with 0.28.3 and I can see "on_confirm_pop" printed when clicking "Back" on "Store" screen:

import flet as ft


def main(page: ft.Page):
    page.title = "Routes Example"

    def route_change(e):
        page.views.clear()

        def confirm_route_pop(e):
            print("on_confirm_pop")
            e.control.confirm_pop(True)

        page.views.append(
            ft.View(
                "/",
                [
                    ft.AppBar(title=ft.Text("Flet app"), bgcolor=ft.Colors.YELLOW),
                    ft.Button("Visit Store", on_click=lambda _: page.go("/store")),
                ],
                can_pop=False,
                on_confirm_pop=confirm_route_pop,
            )
        )
        if page.route == "/store":
            page.views.append(
                ft.View(
                    "/store",
                    [
                        ft.AppBar(title=ft.Text("Store"), bgcolor=ft.Colors.YELLOW),
                        ft.Button("Go Home", on_click=lambda _: page.go("/")),
                    ],
                    can_pop=False,
                    on_confirm_pop=confirm_route_pop,
                )
            )
        page.update()

    def view_pop(e):
        page.views.pop()
        top_view = page.views[-1]
        page.go(top_view.route)

    page.on_route_change = route_change
    page.on_view_pop = view_pop

    page.go(page.route)


ft.app(main)

[SIRGPrice]

Absolutely, it works perfectly on desktop. But when I do the next secuence of things:

• Build the apk of this example or other combinations and try it in Android Studio Emulator or in a real mobile android device.

• With the View 's property can_pop set to False.

• With the View 's event on_confirm_pop set to: lambda_ : function(args)

• And you press the android sistem back button to go back.

Then the button does nothing because the property can_pop = False is disabling the pop event, not on_confirm_pop or page.on_view_pop event is generated.

If can_pop=True pressing android sistem button generates pop event that pops a view directly, without the oportunity to have logic between.

In the 2 cases android back sistem button give no oportunity to display pop logic.

Thats only on android once apk done.

Thanks Feodor.

[FeodorFitsner]

OK, I just bumped Flet version in Flet build template. Delete "build" folder of your app and rebuild.

[SIRGPrice]

I tryed again with the new build template and Flet dont catch any event associated with sistem back button on mobile device when can_pop=False. So page.on_view_pop and on_confirm_pop are never being called.

I think could be a personal code issue, but it seems imposible to me to reach a combination that makes any sistem back button associated event handler being fired when can_pop = False when testing in device.

[SIRGPrice]

Im going to try some hipersimplistic variants so I can give you more feed back about it.

Thanks.

[FeodorFitsner]

What version of Flet do you have inside of your APK? It's in libpythonsitepackages.so (it's just renamed zip).

[SIRGPrice]

Fonunded in version.py inside libpythonsitepackages.so:

"""Provide the current Flet version."""

import os
import subprocess as sp
from pathlib import Path

import flet
from flet.utils import is_mobile, is_windows, which

will be replaced by CI
version = "0.28.3"

...

[FeodorFitsner]

Can you do a simple code repro for me please?

[SIRGPrice]

Sure!

from flet import *
import time

def main(page: Page):

    G = Colors.LIGHT_GREEN_ACCENT_400
    B = Colors.BLUE_400
    R = Colors.PINK_ACCENT_400
    D = Colors.DEEP_PURPLE_900

    # main page, not popable, all other view return here.

    view0 = View(
        route="/0",
        can_pop=False,
        controls=[SafeArea(expand=True, content=Container(
                height=page.height,
                width=page.width,
                bgcolor=R,
                content=Column([Container(Icon(Icons.MENU,color=D),on_click=lambda _: go(1)),
                                Container(Icon(Icons.HOME,color=D),on_click=lambda _: go(2))])
            ))
        ]
    )

    # secondary pages

    view1 = View(
        route="/1",
        can_pop=False,
        on_confirm_pop=lambda e: Pop(e),
        controls=[SafeArea(expand=True, content=Container(
                height=page.height,
                width=page.width,
                bgcolor=G,
                content=Container(Icon(Icons.MENU,color=D),on_click=lambda _: go(0))
            ))
        ]
    )

    view2 = View(
        route="/2",
        can_pop=False,
        on_confirm_pop=lambda e: Pop(e),
        controls=[SafeArea(expand=True, content=Container(
                height=page.height,
                width=page.width,
                bgcolor=B,
                content=Container(Icon(Icons.HOME,color=D),on_click=lambda _: go(0))
            ))
        ]
    )

    def go(view): # poping the old view and pushing the new one on top.

        print("go")

        if len(page.views) == 2: # max number of views that want to be acumulated in page.views.

            page.views.pop(0)
            page.views[0].confirm_pop = True

        if view == 0:
            new_view = view0
        elif view == 1:
            new_view = view1
        elif view == 2:
            new_view = view2

        page.views.append(new_view)
        page.update()

    def Pop(e):

        print("Pop")

        time.sleep(0.5) # pop logic

        e.control.confirm_pop = True # explicitly confirming the pop of the last view

        # also valid

        #page.views[-1].confirm_pop = True

    go(0) # starting the app with the first view

app(target=main, assets_dir="assets")

When I build this apk with the same toml and everything, it gives the same result as my real code, pushing sistem back button not firing on_confirm_pop.

[SIRGPrice]

Hi Feodor, was posible for you to reproduce it? Its the simplest example I can do.

I'm in no hurry, it's just in case you needed more information.

[FeodorFitsner]

Looking into that.