Uno.Extension-Navigation: use existing ViewModel

[TopperDEL]

How is the following with Uno.Extensions supposed to work: if I have a ListView bound to a collection of "ItemViewModels" and click one entry - how can I navigate to a View that gets the DataContext set to that selected ItemViewModel (instead of creating a new/empty one for the view)?

I currently send the selected ViewModel as a parameter to the view and set the DataContext manually. But that feels not right.

[nickrandolph]

Hey, check out this how-to guide and let me know if you still need a hand: https://platform.uno/docs/articles/external/uno.extensions/doc/Learn/Tutorials/Navigation/HowTo-DisplayItem.html

[TopperDEL]

Yeah, I'm doing the opposit quite now - sending my existing ViewModel as nav-parameter and setting it in the View OnNavigatedTo. The above one is better, though, as the OtherPage here does not need to be aware of the OtherPagewViewModel.

[nickrandolph]

@TopperDEL The PR which allows for using an existing ViewModel instance has been merged (see unoplatform/uno.extensions#496). If you update to the latest dev packages for uno extensions (update all packages with prefix Uno.Extensions) it would be great to know whether this addresses your issue?

[TopperDEL]

Thanks @nickrandolph! But unfortunately that does not yet seem to help in my case. But maybe I'm doing something wrong? I'm doing the navigation in my ShellViewModel, as I'm using a MessageBus here. So the view itself does not navigate. I do it like this:

await Navigator.NavigateViewAsync<RoomView>(this, data: eventData.RoomViewModel);

I have a RouteMap like this in place:

new ViewMap<RoomView, RoomViewModel>(),
[...]
new RouteMap("RoomView", View: views.FindByViewModel<RoomViewModel>())

I get to the correct view, but the DataContext hasthe ShellViewModel set (in OnNavigatedTo) which I think is kind of like a default here.

[nickrandolph]

yeh so because of the way WinUI (UWP) does frame navigation the viewmodel isn't necessarily set as the datacontext at the time the onnavigatedto is called. If you want to access the viewmodel in the codebehind, you need to attach an event handler to the DataContextChanged event.

The code you have should be correct - can you put a breakpoint in the RoomViewModel constructor and make sure it doesn't get called during navigation?

[TopperDEL]

Oh, indeed - it is working. I've mixed it up together with my old code to handle the Navigation-data. Awesome! now it is like it should be. Thank you!