Xamarin: ObservableCollection does't automatically update ListView

Question

I have a ListView bounded to an ObservableCollection in the ViewModel. In initialization the ListView items are displayed perfectly. However, when I try to update a single value of an item of ObservableCollection at run-time, the linked item in the listview does not update automatically. It updates only if I scroll the listView. Why does it behave like this?

Here's the code:

XAML

ViewModel

        public static ObservableCollection acquistiList;
        public ObservableCollection AcquistiList
        {
            get { return acquistiList; }
            set
            {
                if (acquistiList != value)
                {
                    acquistiList = value;
                    OnPropertyChanged();
                }
            }
        }

        private void AggiungiArticolo(RigaStoricoModel prodotto, ParametriUM parametriUM)
        {
            double esistenzaUMPredef = parametriUM.EsistenzaUMPredef.GetValueOrDefault(0);

            if (esistenzaUMPredef > 0)
            {
                double qtaMinima = parametriUM.QtaMinima.GetValueOrDefault(1);

                if (prodotto.QtaEdit + qtaMinima <= esistenzaUMPredef)
                {
                    prodotto.QtaEdit += qtaMinima;  // <-- here the update not working
                }
            }

Leon Lu · Accepted Answer

Do you want to achieve the result like following GIF?

If so, you should achieve the INotifyPropertyChanged interface in your RigaStoricoModel as Silvermind's said.

Here is MyViewModel.cs code.

   public class RigaStoricoModel: INotifyPropertyChanged
    {

        private double _qtaEdit;
        public double QtaEdit
        {
            set
            {

                _qtaEdit = value;

                OnPropertyChanged("QtaEdit");

            }
            get => _qtaEdit;
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

I used AggiungiCommand to make a test(decrease or increase).

    public class MyViewModel
    {
        public static ObservableCollection acquistiList;
        public ObservableCollection AcquistiList
        {
            get { return acquistiList; }
            set
            {
                if (acquistiList != value)
                {
                    acquistiList = value;
                  //  OnPropertyChanged();
                }
            }
        }

        public ICommand AggiungiCommand { protected set; get; }
        public ICommand AggiungiCommand2 { protected set; get; }

        //  public int MyProperty { get; set; }

        public MyViewModel()
        {
            AcquistiList = new ObservableCollection();
            AcquistiList.Add(new RigaStoricoModel() { QtaEdit=0.28 });
            AcquistiList.Add(new RigaStoricoModel() { QtaEdit = 0.38 });
            AcquistiList.Add(new RigaStoricoModel() { QtaEdit = 0.48 });
            AcquistiList.Add(new RigaStoricoModel() { QtaEdit = 0.58 });
            AcquistiList.Add(new RigaStoricoModel() { QtaEdit = 0.68 });

            AggiungiCommand2=new Command(async (key) =>
            {
                RigaStoricoModel model = key as RigaStoricoModel;
                model.QtaEdit += 0.1;

            });
            AggiungiCommand = new Command(async (key) =>
            {
                RigaStoricoModel  model= key as RigaStoricoModel;
                model.QtaEdit -= 0.1;

            });
        }
    }
}

Here is layout.xaml(I do not have this style, for testing,I delete them and adjust this layout).

Here is layout background code.

    public MainPage()
        {
            InitializeComponent();

            this.BindingContext = new MyViewModel();
        }

Xamarin: ObservableCollection does't automatically update ListView

Answers (1)

Related Questions

Xamarin: ObservableCollection does&#39;t automatically update ListView

Answers (1)

Related Questions

Xamarin: ObservableCollection does't automatically update ListView