Navigation and pass parameters.

[Midnayt]

Sorry for disturbing, but I check sample and docs and didn't find how can pass params with navigation. if it's possible, can you provide some example how to handle it.

[albyrock87]

You're not the first one asking, so I should probably update the docs with a specific simple example :)

So here it is in the mean time.

Let's say you have your ContactsPageModel and when the user presses on a contact, you want to open a ContactDetailPageModel for the tapped contact.

Inside ContactsPageModel you should have your command (here I'm using CommunityToolkit MVVM as an example).

public Task ContactSelected(Contact contact)
{
    // Create navigation descriptor
    var navigation = Navigation.Relative()
                               .Push<ContactDetailPageModel>()
                               .WithIntent(contact);
    // Invoke Nalu's INavigationService
    return _navigationService.GoToAsync(navigation);
}

The method WithIntent is what you need to pass a typed parameter to the target view model.

Then your ContactDetailPageModel class should implement either (or both) IEnteringAware<Contact> or IAppearingAware<Contact> depending on where you want to load the contact information inside the page.

So let's suppose loading contact information takes a while, and you want your page to display a loader and when the page appears you start loading information.

IEnteringAware<Contact> would block the navigation until the contact information is ready which is what we do not want as we prefer a fast navigation.

So you would implement IAppearingAware<Contact> in this specific case.

public partial class ContactDetailPageModel(IContactLoadingService contactLoadingService)
    : ObservableObject, IAppearingAware<Contact>
{
    public async ValueTask OnAppearingAsync(Contact contact)
    {
        this.ContactDetails = await contactLoadingService.LoadContactDetails(contact);
    }
}

Refer to Navigation Events section in the documentation for more details/use cases.

[CodingOctocat]

Is it possible to understand that IEnteringAware<Intent> like IQueryAttributable?

[albyrock87]

@CodingOctocat IEnteringAware may be triggered at the same time of IQueryAttrinutable but only in a special situation: when the page is created for the first time.

For example, let's say you have ShellContent page A.

When you push B it will trigger IEnteringAware as soon as B instance is created and IAppearingAware as soon as the underlying navigation completes.

But if you then push C and pop C again go back to B, then only IAppearingAware will be triggered on B.

Does this clarify?

[CodingOctocat]

Thank you! In my implementation of ApplyQueryAttributes, I have if (_isInitialized) return; preventing duplicate fetching of navigation parameters, which I should be able to simplify if I use IEnteringAware.

[albyrock87]

@CodingOctocat correct 💯

[Midnayt]

@albyrock87 Thanks. one more question, I saw in documentation Navigation.Relative() and Navigation.Absolute() - whats difference?

[albyrock87]

A relative navigation starts from the current page, while absolute starts from the root.

So if your current navigation stack is A > B > C and you want to go back to A (where A is the view model of the shell content):

• with relative navigation you can do .Pop().Pop()
• with absolute you can just .ShellContent<A>()

It all depends on your needs.