Navigation Cancellation Support for NavigateAsync and NavigateAndWaitAsync

[gentledepp]

What is missing?

When a Page A navigates to Page B, Page B may determine in its InitializeAsync method, that the navigation is incorrect and should be cancelled.
This is currently not possible.

How should this be implemented

The easies option is to let Page B call INavigator.BackAsync.
Should a navigation still be "in progress", that flow should be cancelled.

In our example, Page A's navigation to Page B is still in progress when Page B calls INavigator.BackAsync in it's InitializeAsync method.
In that case, the INavigator should simply navigate back to Page A

Why is this feature important?

• Conditional Navigation: Pages can decide at runtime whether
  they should be displayed based on user permissions, data
  availability, or other conditions
• User Experience: Prevents users from seeing pages that should
  be redirected or cancelled
• Navigation Chains: Supports complex navigation flows where
  pages navigate to other pages that might cancel the entire
  chain

[OmidID]

Hello @gentledepp

Thanks for the details and the effort.

As I remember, in the OnNavigating you have this possibility to cancel the navigate.

As your use case of user access permission, Normally this flow should be check before navigation. In additional can you split this PR in 2? One for add UT and one to implement this feature in case.

In additional in your PR, can you respect the line intents please?

Thanks again.

[gentledepp]

Thanks for the input!
OnNavigating is another approach I did not know about.
However, my problem specifically is, that we navigate to a page that can take quite a while to load (loads data and computes). For this reason I show a progress bar and allow the user to cancel the navigation that way.

I will think about splitting the PR, if you like. But this may take some time since I am on holiday for the next few weeks.

[OmidID]

Hello @gentledepp
I hope you had a good vacation :)

Do you have time to split the PR?

[gentledepp]

not yet. will do next week! I promise