Xamarin Forms Prism Pass a property via CommandParameter - mvvm

Question

I don't know how I can pass a single property via CommandParameter to my Command function in the ViewModel.
Now I pass the whole object (CategoryListItem) but I only need the value from the Id property. How can I achieve this?
Class:
public class CategoryListItem
{
public int Id { get; set; }
public int Order { get; set; }
public string Name { get; set; }
}
ViewModel:
public ObservableRangeCollection<CategoryListItem> Listing
{
get => _listing;
set => SetProperty(ref _listing, value);
}
OnItemTappedCommand = new DelegateCommand<CategoryListItem>(OnItemTapped);
private async void OnItemTapped(CategoryListItem obj)
{
await _navigationService.GoBackAsync(new NavigationParameters
{
{ "CategoryId", obj.Id }
});
}
XAML:
<ListView
ItemsSource="{ Binding Listing }"
HasUnevenRows="false"
CachingStrategy="RecycleElement"
SeparatorColor="{ DynamicResource AccentColor }">
<ListView.Behaviors>
<b:EventToCommandBehavior
EventName="ItemTapped"
Command="{ Binding OnItemTappedCommand }"
CommandParameter="???"
EventArgsConverter="{ StaticResource ItemTappedEventArgsConverter }">
</b:EventToCommandBehavior>
</ListView.Behaviors>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Label
Text="{ Binding Name }"
VerticalTextAlignment="Center"
HorizontalTextAlignment="Center"
FontSize="16" />
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Converter:
public class ItemTappedEventArgsConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is ItemTappedEventArgs itemTappedEventArgs))
{
throw new ArgumentException("error");
}
return itemTappedEventArgs.Item;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Any ideas are welcome! Nothing worked for me.

Answer 1

i think you don't need to use CommandParameter,you could return the CategoryListItem.Id directly in your ItemTappedEventArgsConverter:
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is ItemTappedEventArgs itemTappedEventArgs))
{
throw new ArgumentException("error");
}
return ((CategoryListItem)itemTappedEventArgs.Item).Id;
}
then in you ViewModel :
OnItemTappedCommand = new DelegateCommand<int>(OnItemTapped);
private async void OnItemTapped(int id)
{
// here you could get the Id property
}

Answer 2

I don't think you can bind to the tapped record from there. You might be able to do something in your ItemTemplate like create a behavior on the view cell and pass the property from there.
If you want to avoid the converter you could use "EventArgsParameterPath" instead:
<b:EventToCommandBehavior
EventName="ItemTapped"
Command="{Binding OnItemTappedCommand}"
EventArgsParameterPath="Item">
</b:EventToCommandBehavior>
Set it to "Item" and it will still send the entire CategoryListItem.
See documentation here:
https://prismlibrary.github.io/docs/xamarin-forms/EventToCommandBehavior.html