Blocking Navigation¶

You may want to prevent the user from navigating away from a page, for example, if they are editing a form.

from routing.router import RoutingContext, navigate, confirm


class EditForm(EditFormTemplate):
    def __init__(self, routing_context: RoutingContext, **properties):
        self.routing_context = routing_context
        self.routing_context.register_blocker(self.prevent_navigation)
        super().__init__(**properties)

    def prevent_navigation(self, **event_args):
        c = confirm(
            "Are you sure you want to leave this page? Your changes will be lost."
        )
        return not c

    def save_button_click(self, **event_args):
        self.routing_context.unregister_blocker(self.prevent_navigation)
        navigate(path="/dashboard")

Alternatively, you can use the NavigationBlocker context manager.

from routing.router import NavigationBlocker, alert


class Form(FormTemplate):
    def __init__(self, **properties):
        super().__init__(**properties)

    def run_important_alert(self, **event_args):
        with NavigationBlocker(warn_before_unload=True):
            alert("Important Alert", dismissible=False)

The above navigation blocker will prevent the user from navigating away from the page while the alert is open. warn_before_unload will show the browser dialogue asking if the user wants to leave the page if they navigate to a new website. By default, this is False.

Alerts¶

The alert and confirm functions are provided by the routing library. These functions behave similarly to Anvil's default alert and confirm functions, but they block navigation when dismissible=False and close when navigation occurs if dismissible=True. The default is True for alert and False for confirm.

You can override the default alert and confirm functions by setting the anvil.alert and anvil.confirm attributes in your startup module.

# startup.py
import anvil
from routing import router

anvil.alert = router.alert
anvil.confirm = router.confirm

if __name__ == "__main__":
    router.launch()