CODEWITHSUNDEEP
c#system.reactivereactiveui
PapaStoke
PapaStoke

Reputation: 158

WhenAny and ToProperty

I think I am missing a fundamental Observable concept.

I have a ChargeViewModel class which has a ReactiveList property which is a collection of itself ChargeViewModel.Charges which contains related charges

I want to observe the latest entry in the charges collection (it has a ChargeViewModel.lastModified) and also have other properties in the UI based on the latest entry.

In the ctor I have this code which works to initialize the values; however it does not update the values for latestActionDate, latestBillToName, lastestNote when the observable variable "last" changes

I want the UI to update if the user updates the "last" charge or creates a new "last".

var last = Charges?
             .Changed
             .Select(_ => Charges.OrderByDescending(c => c.Model.LastModified).FirstOrDefault())
             .StartWith(Charges.OrderByDescending(c =>c.Model.LastModified).FirstOrDefault());

last
  .Select(c => c.Model.LastModified)
  .ToProperty(this, vm => vm.LatestActionDate, out latestActionDate);
last
  .Select(c => c.Model.BillToName)
  .ToProperty(this, vm => vm.LatestBillToName, out latestBillToName);
last
   .Select(c => c.Model.Note)
   .ToProperty(this, vm => vm.LatestNote, out latestNote);

Upvotes: 1

Views: 218

Answers (1)

Gluck
Gluck

Reputation: 2962

ReactiveList (by default) only notifies upon elements added/moved/removed, not upon content changes. It's fairly simply to enable it (and maybe you already did) by setting ChangeTrackingEnabled=true.

However when enabled, you'll receive such motifications on ItemChanged observable, and not on Changed one, so in your case you probably need to do:

Charges.Changed.Select(_ => Unit.Default).Merge(Charges.ItemChanged.Select(_ => Unit.Default))
    .Select(_ => /* ... */)
    ....

Upvotes: 2

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