Xamarin.Forms ListView with ReactiveUI does not update new items

Question

I am developing a Xamarin.Forms app. It have SearchBar in the NavigationBar, ListView in the ContentPage and a Entry with AddButton in the bottom. When user click on the AddButton the text in the Entry adds to the realm mobile database. Which autorefresh the IEnumerable. The ListView that is bind to IEnumerable auto updates.

 public class MainViewModel : ReactiveObject
{

    public IEnumerable<Company> Companies { get; set; }

    [Reactive]
    public string Query { get; set; }

    public string NewCompany { get; set; }

    public ReactiveCommand<Unit, Unit> AddCompanyCommand { get; set; }
    public ReactiveCommand<Unit, IEnumerable<Company>> SearchCommand { get; set; }

    Realm _realm;

    public MainViewModel()
    {

        _realm = Realm.GetInstance();

        Companies = _realm.All<Company>();

        AddCompanyCommand = ReactiveCommand.CreateFromTask(async () => await AddButtonClicked());
        SearchCommand = ReactiveCommand.Create<Unit, IEnumerable<Company>>(
            _ =>

            SortCollection()
            );


        SearchCommand.ToProperty(this, nameof(Companies));

        this.WhenAnyValue(x => x.Query).Throttle(TimeSpan.FromSeconds(1)).Select(_ => Unit.Default).InvokeCommand(this, x => x.SearchCommand);


    }

    async Task AddButtonClicked()
    {
        if (!string.IsNullOrWhiteSpace(NewCompany))
        {
            _realm.Write(() =>
            {
                _realm.Add(new Company { Name = NewCompany });
            });
            NewCompany = string.Empty;
        }
    }

    IEnumerable<Company> SortCollection()
    {
        if (string.IsNullOrWhiteSpace(Query))
        {
            Companies = Companies.Where(x => x.Name != string.Empty);
        }
        else
        {
            Companies = Companies.Where(x => x.Name.IndexOf(Query, StringComparison.InvariantCultureIgnoreCase) >= 0);
        }

        return Companies;


    }

}

Recently when I added Search Logic to the ViewModel the ListView is not Auto Updating. I either have to search or restart the app to display the new item in the ListView. When I comment out the following line the ListView starts auto updating.

 SearchCommand.ToProperty(this, nameof(Companies));

But then it stops displaying Search Results. I want both Auto updating with new item and displaying search result functionalities in the ListView.

score 0 · Answer 1 · answered Aug 09 '19 at 05:11

0

At first glance, your public IEnumerable<Company> Companies { get; set; } isn't notifying property change events.

answered Aug 09 '19 at 05:11

Rodney Littles

544
2
11

But it start notifying if I comment out: " SearchCommand.ToProperty(this, nameof(Companies));". – Paramjit Aug 09 '19 at 05:14
This same line which is interfering with updating ListView with new Items, is correctly updating the ListView with SearchResults. – Paramjit Aug 09 '19 at 05:24
1

Your not doing anything with your ToProperty. – Glenn Watson Aug 09 '19 at 12:39

score 0 · Answer 2 · answered Aug 09 '19 at 05:55

0

The fact that you need to tell the runtime that the property has changed so you need to implement notify property changed interface Look at this another stackoverflow thread.

Implementing INotifyPropertyChanged - does a better way exist?

Also there is is a plugin named fody which automatically injects propertychanged code into every setter of the properties in the project. Without needing you to do anything.

Install both of them in the project where you are writing your properties, it will automatically inject property changed code while compiling. https://www.nuget.org/packages/Fody/ https://www.nuget.org/packages/PropertyChanged.Fody/

answered Aug 09 '19 at 05:55

prasadsunny1

775
6
15

I am using realm and it updates the collection and notifies the view automatically. I am already using ReactiveUI.Fody. But I don't need that on my Companies collection. – Paramjit Aug 09 '19 at 05:59
ObserableAsPropertyHelper does inotifyprooertychanged notifications. – Glenn Watson Aug 09 '19 at 12:38

Xamarin.Forms ListView with ReactiveUI does not update new items

2 Answers2