How to bind a List or List to a UserControl.List?

Question

I have an Interface and two classes.

public interface IFieldValue
{
  Int64 FieldId { get; set; }
  string Value { get; set; }
}

public class CarFieldValue : IFieldValue
{
  public Int64 CarId { get; set; }
  public Int64 FieldId { get; set; }
  public string Value { get; set; } 
}

public class HouseFieldValue : IFieldValue
{
  public Int64 HouseId { get; set; }
  public Int64 FieldId { get; set; }
  public string Value { get; set; } 
}

Now I have a generic usercontrol for displaying the field values of either Car or House. The usercontrol is bound to the according ViewModel.

public class CarViewModel : INotifyPropertyChanged
{
  (...)

  private ObservableCollection<CarFieldValue> _FieldValues;
  public ObservableCollection<CarFieldValue> FieldValues
  {
    get { return _FieldValues; }
    set
    {
      if (_FieldValues!= value)
      {
        _FieldValues= value;
        SendPropertyChanged("FieldValues");
      }
    }
  }
}

and

public class HouseViewModel : INotifyPropertyChanged
{
  (...)

  private ObservableCollection<HouseFieldValue> _FieldValues;
  public ObservableCollection<HouseFieldValue> FieldValues
  {
    get { return _FieldValues; }
    set
    {
      if (_FieldValues!= value)
      {
        _FieldValues= value;
        SendPropertyChanged("FieldValues");
      }
    }
  }
}

The usercontrol part looks like this:

public IReadOnlyList<IFieldValues> FieldValues
{
  get { return (IReadOnlyList<IFieldValues>)GetValue(FieldValuesProperty); }
  set { SetValue(FieldValuesProperty, value); }
}
public static readonly DependencyProperty FieldValuesProperty = DependencyProperty.Register("FieldValues", typeof(IReadOnlyList<IFieldValues>), typeof(FieldValuesControl), new UIPropertyMetadata(null));

The binding takes place in XAML in the Views, e.g. in the CarView:

<myCtrls:FieldValuesControl FieldValues="{Binding MyCarViewModel.FieldValues}" />

I found that solution here]1 and it works so far. But I need to edit (add or remove) items in the usercontrol. When I use an IList<IFieldValues> instead of IReadOnlyList<IFieldValues> the binding doesn't work. There are no binding errors/warnings.

I also tried ICollection<IFieldValues> without success. I could use IEnumerable<IFieldValues> as suggested in the comments but then I can't Add() items because I can't cast the IEnumerable.

How can I implement this scenario?

Update Since I didn't find a better solution I use ObservableCollection<IFieldValues> on both the ViewModels and the usercontrol. As my ViewModels doesn't do much with the Lists it's not to complicated. Thanks for your help.

Just a shot in the dark - have you tried specifying a OneWay binding? — LordWilmore, Jul 12 '16 at 08:12
@Clemens: Yes, `IEnumerable does work, but I need to add/remove items in the usercontrol. I can`t cast the `IEnumerable` there to a `List` or `ObservableCollection`. Sorry, going to make that more clear in the question. — gumo, Jul 12 '16 at 09:33
If you need to add items in the user control, you can't operate on a specialized list. However, you can hold a copy of the list items in a separate list of matching type. Something like `List items = srcList.Cast().ToList()` — grek40, Jul 12 '16 at 11:35

score 0 · Answer 1 · edited May 23 '17 at 11:44

0

Why you don't use a ObservableCollection or an IEnumerable in your UserControl?

Like other do:

And I think your problem is the same as here

Problem is in your DependencyProperty registration. Co-variance is not applicable for generic lists

Another possibility would be to use the ItemCollection class. The same is used from the default ItemsControl (see code).

edited May 23 '17 at 11:44

Community

1
1

answered Jul 12 '16 at 08:15

wake-0

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Using an `ObservableCollection` leeds to binding errors because you can 't bind an explicit `ObservableCollection` respectively `ObservableCollection` to an generic `ObservableCollection`. `IEnumerable` and `IList` don't work too. Only `IReadOnlyList`. I haven't figured out the difference yet. – gumo Jul 12 '16 at 08:47
@gumo Have you tried `ObservableCollection – wake-0 Jul 12 '16 at 09:00
Using `object` has the same binding error as `ObservableCollection` "System.Windows.Data Error: 1 : Cannot create default converter to perform 'one-way' conversions between types 'ObservableCollection`1[CarFieldValue]' and 'ObservableCollection`1[Object]'. Consider using Converter property of Binding..." – gumo Jul 12 '16 at 09:14
@gumo the idea behind using means that the `ObservableCollection` from the `ViewModels` uses `object` too – wake-0 Jul 12 '16 at 09:19
Ah, OK, now I understand. I would like to avoid the then neccessary casting from object to `IFieldValues`. I will try `ItemCollection`. – gumo Jul 12 '16 at 09:34

How to bind a List or List to a UserControl.List?

1 Answers1