Shell, Navigation and Page instantiation

[ioiooi]

Hello,

are Pages that are defined in the visual hierarchy only ever instantiated once? And if that is the case is there a way to clear the cache and force the creation of a new Page instance the next time I navigate to it?

For example the following hierachy is described in a AppShell.xaml:

<ShellContent Route="LoginPage" Shell.FlyoutBehavior="Disabled" ContentTemplate="{DataTemplate local:LoginPage}" />

<FlyoutItem FlyoutDisplayOptions="AsMultipleItems">
    <ShellContent Title="About" Icon="tab_about.png" Route="AboutPage" ContentTemplate="{DataTemplate local:AboutPage}" />
    <ShellContent Title="Browse" Icon="tab_feed.png" ContentTemplate="{DataTemplate local:ItemsPage}" />
</FlyoutItem>

<ShellContent Route="SecretPage" Shell.FlyoutBehavior="Disabled" ContentTemplate="{DataTemplate local:SecretPage}" />

The LoginPage constructor gets called when the App is started. Navigate to the AboutPage with Shell.Current.GoToAsync($"//{nameof(AboutPage)}") and its constructor gets called.

Now lets say the AboutPage has a Logout-Button which does some things and at the end it calls Shell.Current.GoToAsync($"//{nameof(LoginPage)}"). The LoginPage constructor does not get called. Navigate back from the LoginPage to the AboutPage and its constructor also does not get called.

The same deal if I would navigate from the LoginPage to the SecretPage. The constructor of SecretPage would only get called the first time.

Lets say I use ViewModels for all those Pages. I can't really create a state in the ViewModel constructor because the Page only gets instantiated once and so in my case the ViewModel also only gets instantiated once. I would need to do the work in a OnAppearing.

I would want for the Pages after the LoginPage to always be newly constructed in order to make sure that theres a clean state.

PS:
A lot of examples also contain DetailsPages... something like ItemsDetails, MonkeyDetails, CatDetails etc... Those Pages are never declared in the AppShell.xaml but are registered like so

Routing.RegisterRoute("monkeys/details", typeof(MonkeyDetailPage));

and from what Ive seen seem to be always instantiated every single time theyre navigated to.

[NickDevoctomy]

Hello, I was just wondering if you had managed to find a solution for this? I could also do with handing page instantiation this way. Have you tried asking in the MAUI Q&A site?

https://docs.microsoft.com/en-us/answers/topics/460228/dotnet-maui.html

[ioiooi]

Hi, nope sorry, I haven't found a solution for this.

In my case I just want to be sure that everything starts fresh after a Logout and that there are no residual objects or whatever from the previous User/Session. My workaround for this specific case is to create a new AppShell after a Logout. It looks something like this:

public void Logout()
{
    Application.Current!.MainPage = new AppShell();
}

cheers

[ederbond]

Thanks @ioiooi your workaround seems to work fine for me, I'm just not sure if it could let us to any other issue like a memory.

[Hooterr]

Has anyone looked into this, if it causes any memory issues?

[MV10]

That Q&A site is awful...

@Hooterr see issue 9300; somebody from MS confirms that shouldn't leak.

There is also a workaround in this comment.

[shadowfoxish]

Heh, I had the same question in a more roundabout way
#16295