通过更改的RealmList <>更新ListView

Question

Suppose this data model based on realm.io :

public class JournalEntry : RealmObject {
        ...
}

public class JournalOwner : RealmObject {
        ...
        public RealmList<JournalEntry> Entries { get; } 
}

I have a JournalEntriesPage , which show a ListView of all JournalEntry items of a JournalOwner .

Inside the corresponding view model, I pass the JournalOwner to the constructor and assign the JournalOwner.Entries to the property Entries .

public class JournalEntriesViewModel {

        private Realm _realm;

    private JournalOwner _owner;
    public RealmList<JournalEntry> Entries { 
        get { return _owner.Entries; }
    }
    ....
    public JournalEntriesViewModel( JournalOwner owner ) {

        _realm = Realm.GetInstance();
        _owner = owner;

        AddEntryCommand = new Command(AddEntry);
        DeleteEntryCommand = new Command<JournalEntry>(DeleteEntry);

    }

If I add a JournalEntry via the UI, it gets created but does not appear in the ListView .

If I move up the Navigation (to JournalOwner ) and then down to the entries of the owner, the ListView shows the newly created JournalEntry .

Somehow, the ListView of JournalEntry s does not know about the newly created JournalEntry.

The JournalEntriesPage binds the ListView like so:

<ListView 
   ItemsSource="{Binding Entries}" 
   x:Name="EntriesListView" 
   ItemTapped="OnItemTapped"     
   ItemSelected="OnItemSelected" >

How Do I mange the ListView show newly created entries immediately?

I feel, that I somehow need to inform observers (?) of Entries that its value changed.

In a corresponding situation, changes to the entries of

Owners = _realm.All<JournalOwner>();

do force the corresponding ListView to change immediately.

Answer 1

RealmList<T> does not implement INotifyCollectionChanged as @Jason has pointed out and so it cannot notify the ListView of changes. Your best bet would be to manually reload the data in the ListView.

RealmResults<T> on the other hand does implement INotifyCollectionChanged (though the API around that will soon change slightly ). That's why a ListView bound to _realm.All<JournalOwner>() updates according to changes in the database.

The underlying infrastructure for observable lists is there , it's just a matter of time before it's exposed at the C#-level.