Question

I have a problem with the following scenario (code cut for brevity). Basically the Setter of my User Control Property isn’t being called when the dependency property is set and I need to get around this.

I have the following code in my View.xaml

<Filter:Filter x:Name="ProductFilter" PrimaryItemSource="{Binding CarrierProducts}"  />

In the View.xaml.cs

    public ProductPricing()
    {
        InitializeComponent();

        ViewModel.Filter.ProductPricing vm = new ViewModel.Filter.ProductPricing();
        this.DataContext = vm;
    }

In my ViewModel I expose a property

    public ObservableCollection<Model.FilterItem> _carrierProducts;
    public ObservableCollection<Model.FilterItem> CarrierProducts
    {
        get
        {
            return _carrierProducts;
        }
        set
        {
            if (_carrierProducts != value)
            {
                _carrierProducts = value;
                RaisePropertyChanged("CarrierProducts");
            }
        }
    }

Finally the Filter User control is defined like so.

   public static readonly DependencyProperty PrimaryItemSourceProperty =
        DependencyProperty.Register("PrimaryItemSource", typeof(ObservableCollection<Model.FilterItem>), typeof(Filter), new PropertyMetadata(null));

    public ObservableCollection<Model.FilterItem> PrimaryItemSource
    {
        get
        {
            return (ObservableCollection<Model.FilterItem>)GetValue(PrimaryItemSourceProperty);
        }

        set
        {
            SetValue(PrimaryItemSourceProperty, value);

            ComboBox combo = _filters.ElementAt(0);
            FilterSourceChange(combo, value);
        }
    }

For some reason the PrimaryItemSource property is set but the Setter doesn’t get called. Do I have to add a PropertyChange event to the PropertyMetadata object to handle this as that seems like a lot of code for something simple.

Answer 1

Yes, always use the callback if you need additional logic for the setter. This is a must in Silverlight and WPF.

As far as I know, the Setter would only be called when actually used from code. When you do Binding, things happen using the DependencyProperty framework.

You should also wrap your ComboBox combo = ... code into a this.Dispatcher.BeginInvoke(() => ... );, because that ensures the visual tree is initialized.