The line Resources.Add("eventAggregator", Container.Resolve()); raises Null exception.
UPDATE I've added all classes to explain more. As @Axemasta said, there is no need to register IEventAggregator and I removed registration. Now I don't how to connect the Listview EventAggregator behavior to the EventAggregator.
This is whole App.xaml code file.
public partial class App : PrismApplication
{
/*
* The Xamarin Forms XAML Previewer in Visual Studio uses System.Activator.CreateInstance.
* This imposes a limitation in which the App class must have a default constructor.
* App(IPlatformInitializer initializer = null) cannot be handled by the Activator.
*/
public App() : this(null) { }
public App(IPlatformInitializer initializer) : base(initializer) { }
protected override async void OnInitialized()
{
InitializeComponent();
Resources.Add("eventAggregator", Container.Resolve<IEventAggregator>());// Removed on update
FlowListView.Init();
await NavigationService.NavigateAsync("NavigationPage/MainPage");
}
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterForNavigation<NavigationPage>();
containerRegistry.RegisterForNavigation<MainPage>();
}
}
}
The behavior class:
public class ScrollToMyModelBehavior : BehaviorBase<ListView>
{
private IEventAggregator _eventAggregator;
public IEventAggregator EventAggregator
{
get => _eventAggregator;
set
{
if (!EqualityComparer<IEventAggregator>.Default.Equals(_eventAggregator, value))
{
_eventAggregator = value;
_eventAggregator.GetEvent<ScrollToMyModelEvent>().Subscribe(OnScrollToEventPublished);
}
}
}
private void OnScrollToEventPublished(ListItem model)
{
AssociatedObject.ScrollTo(model, ScrollToPosition.Start, true);
}
protected override void OnDetachingFrom(ListView bindable)
{
base.OnDetachingFrom(bindable);
// The Event Aggregator uses weak references so forgetting to do this
// shouldn't create a problem, but it is a better practice.
EventAggregator.GetEvent<ScrollToMyModelEvent>().Unsubscribe(OnScrollToEventPublished);
}
}
The Event class:
public class ScrollToMyModelEvent : PubSubEvent<ListItem>
{
}
The page view model:
public MainPageViewModel(INavigationService navigationService, IEventAggregator eventAggregator)
: base (navigationService)
{
Title = "صفحه اصلی";
ListHeight = 100;
ListWidth = 250;
_eventAggregator = eventAggregator;
Items items = new Items();
ListViewItemSouce = items.GetItems();
MyModels = items.GetItems();
SelectedModel = ListViewItemSouce[3];
_eventAggregator.GetEvent<ScrollToMyModelEvent>().Publish(SelectedModel);
}
The page view:
<StackLayout HorizontalOptions="Center" VerticalOptions="Center" WidthRequest="{Binding ListWidth}" HeightRequest="{Binding ListHeight}"
Grid.Row="1" Grid.Column="1">
<local:NativeListView x:Name="lst3" ItemsSource="{Binding ListViewItemSouce}" Margin="1" BackgroundColor="Transparent" RowHeight="47" HasUnevenRows="false">
<ListView.Behaviors>
<local:ScrollToMyModelBehavior EventAggregator="{StaticResource eventAggregator}" /> // Error raised that there is not such a static property
</ListView.Behaviors>
<ListView.ItemTemplate>
<DataTemplate>
<TextCell Text="{Binding Word}" TextColor="Black"/>
</DataTemplate>
</ListView.ItemTemplate>
</local:NativeListView>
</StackLayout>