Xamarin - Bindungsansicht Modell in Xaml

Question

Ich bin eine gruppierte Listenansicht gebunden, um die Modelldatenquelle über XAML anzuzeigen. Aber wenn die App gestartet wird, ist die Liste leer, auch wenn ich sie aus Code hinterher in ctor bevölkere. Wenn ich das ListView x: Name = "myList" deklariere und es aus dem Code bevölkere, funktioniert es, aber es ist nicht direkt an das View-Modell gebunden.

<?xml version="1.0" encoding="utf-8" ?> 
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
      xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
      xmlns:viewModels="clr-namespace:Atc.Obedy.ViewModels;assembly=Atc.Obedy" 
      x:Class="Atc.Obedy.MainPage" Title="Jídelníček"> 
    <ContentPage.Padding> 
    <OnPlatform x:TypeArguments="Thickness" 
       iOS="20, 40, 20, 20" 
       Android="20, 20, 20, 20" 
       WinPhone="20, 20, 20, 20" /> 
    </ContentPage.Padding> 

    <ContentPage.BindingContext> 
    <viewModels:MainPageViewModel /> 
    </ContentPage.BindingContext> 

    <ContentPage.Content> 
    <StackLayout VerticalOptions="FillAndExpand" 
       HorizontalOptions="FillAndExpand" 
       Orientation="Vertical" 
       Spacing="15"> 
     <ListView BindingContext="{ Binding MealsGroups }" GroupDisplayBinding="{ Binding DisplayName }" IsGroupingEnabled="true"> 
     <ListView.ItemTemplate> 
      <DataTemplate> 
      <ViewCell> 
       <StackLayout Orientation="Vertical"> 
        <StackLayout Orientation="Horizontal"> 
        <Label Text="{Binding MealTitle}" /> 
        <Button Image="icon.png" Command="{ Binding OrderCommand }" /> 
       </StackLayout> 
       </StackLayout> 
      </ViewCell> 
      </DataTemplate> 
     </ListView.ItemTemplate> 
     </ListView> 
    </StackLayout> 
    </ContentPage.Content> 
</ContentPage> 

-Code hinter:

public partial class MainPage : ContentPage 
    { 
     protected IMealsRepository MealsRepository { get; } 

     public MainPage() 
     { 
      MealsRepository = IoC.Container.Get<IMealsRepository>(); 

      var mealGroups = new ObservableCollection<MealsGroup>(); 

      foreach (var meals in MealsRepository.GetMeals(DateTime.MinValue, DateTime.MaxValue).Where(x => x.DayOfOrder != null).GroupBy(x=>x.DayOfOrder)) 
      { 
       mealGroups.Add(ProvideMealsGroup(meals.Key.Value, meals)); 
      } 
      InitializeComponent(); 

      var viewModel = BindingContext as MainPageViewModel; 



      viewModel.MealsGroups = mealGroups; 
     } 

Dies ist Ansicht Modell:

public class MainPageViewModel : INotifyPropertyChanged, IViewModel 
    { 
     public event PropertyChangedEventHandler PropertyChanged; 

     private ObservableCollection<MealsGroup> _mealGroups = null; 

     public ObservableCollection<MealsGroup> MealsGroups 
     { 
      get { return _mealGroups; } 
      set 
      { 
       _mealGroups = value; 
       OnPropertyChanged(nameof(MealsGroups)); 
      } 
     } 
     public ICommand OrderCommand { get; set; } 

     public MainPageViewModel() 
     { 
      OrderCommand = new Command(() => 
      { 
       Debug.WriteLine("MealsGroups"); 
      }); 
     } 

     [NotifyPropertyChangedInvocator] 
     protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) 
     { 
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); 
     } 
    } 

Und Mahlzeit Gruppe

public class MealsGroup : List<MealViewModel> 
    { 
     public string DisplayName { get; set; } 
     public string ShortName { get; set; } 

     public event MealGroupOrderSwitched MealGroupOrderSwitched; 

      public ICommand OrderCommand { get; set; } 

      public MealsGroup() 
      { 
       OrderCommand = new Command(() => 
       { 
        Debug.WriteLine("MealGroup"); 
       }); 
      } 

     public void AddMeal(Meal meal) 
     { 
      var model = new MealViewModel 
      { 
       IsOrdered = meal.IsOrdered, 
       MealTitle = meal.MealTitle, 
       MealId = meal.MealId.Value, 
       DayOfOrder = meal.DayOfOrder.Value, 
       IsOrderable = meal.IsOrderable, 
       IsSoup = meal.IsSoup 
      }; 

      model.MealOrdered += meaId => 
      { 
       for (var i = 0; i < Count; i++) 
       { 
        var mealViewModel = this[i]; 
        if (mealViewModel.MealId != meaId && mealViewModel.IsOrderable) 
         mealViewModel.IsOrdered = false; 
       } 
       MealGroupOrderSwitched?.Invoke(this); 
      }; 

      Add(model); 
     } 
    } 

aber die Android-App, wenn hat leere Liste gestartet. Auch wenn ich Artikel in Code hinterher in ctor hinzugefügt habe.

Answer 1

Gelöst durch Ändern der ListView-Eigenschaft xaml BindingContext = {bindenden MealsGroups} an ItemsSource = {bindende MealsGroups}