UserControl with custom ItemsSource doesn't detect changes

Question

I have simple UserControl where is defined property ItemsSource

public static readonly DependencyProperty ItemsSourceProperty =
         DependencyProperty.Register("ItemsSource", typeof(Dictionary<string, object>), typeof(UserControl1), new FrameworkPropertyMetadata(null,
    new PropertyChangedCallback(UserControl1.OnItemsSourceChanged)));

public Dictionary<string, object> ItemsSource
    {
        get { return (Dictionary<string, object>)GetValue(ItemsSourceProperty); }
        set
        {
            SetValue(ItemsSourceProperty, value);
        }
    }

private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            UserControl1 control = (UserControl1)d;
            control.DisplayInControl();
        }

I want to make this property update dynamically, but I am wondered why OnItemsSourceChanged doesn't fired every time when something happend with ItemsSource. So I am upset. I've tried Custom ItemsSource property for a UserControl but this doesn't help or I've written bad newValueINotifyCollectionChanged_CollectionChanged function

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My control is from this post CodeProject

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My Code : UserControl XAML - http://pastie.org/10606317

UserControl CodeBehind - http://pastie.org/10606322

Control Usage -

<controls:MultiSelectComboBox SelectedItems="{Binding SelectedCategories, Mode=TwoWay}" Grid.Column="0" Grid.Row="0" x:Name="CategoriesFilter" DefaultText="Category" ItemsSource="{Binding Categories }" Style="{StaticResource FiltersDropDowns}"/>

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Update : I've made small step to solution. I have next style :

<Style.Triggers>
            <DataTrigger Binding="{Binding ItemsSource, RelativeSource={RelativeSource Self}}" Value="{x:Null}">
                <Setter Property="IsEnabled" Value="False" />
            </DataTrigger>
            <DataTrigger Binding="{Binding ItemsSource.Count, RelativeSource={RelativeSource Self}}" Value="0">
                <Setter Property="IsEnabled" Value="False" />
            </DataTrigger>
        </Style.Triggers>

which I apply to my control (make control disabled if no itemSource). As I update control source on click, I see that control becomes enabled, so ItemsSource aren't empty (from start it is). So problem now is just in Redrawing control content if I understand this behaviour correctly.

Answer 1

If you have a dictionary as your data type, and you add or remove a value from the dictionary, then your property did not actually change. This event will only fire if you have actually set this property to reference a different dictionary.

If you need wpf to automatically detect if an item is added or removed from the dictionary, you should use an ObservableCollection.

Answer 2

1. Replace Dictionary with ObservableCollection, Dictionary won't fire the propertyChanged event when add, update, delete an item.
2. Write your own Dictionary to fire the propertychanged event manually.

Answer 3

I see that the problem is that you are building a new ItemsSource for the ComboBox control within your custom UserControl, and that you are expecting that MultiSelectCombo.ItemsSource to stay synced with your UserControl1.ItemsSource. This can't happen when simply binding a Dictionary, and it won't happen even when binding an ObservableCollection -- unless you explicitly handle it.

To accomplish what you are after, first you will need ItemsSource of your custom control to be of a type that does notify us of collection changes, such as the ObservableCollection (which I'll use for this example, as you've done in your links above). Then, you'll need to update the ItemsSource of your ComboBox within your control, to keep them in sync.

private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var control = (MultiSelectComboBox)d;

    // Since we have to listen for changes to keep items synced, first check if there is an active listener to clean up.
    if (e.OldValue != null)
    {
        ((ObservableCollection<Node>)e.OldValue).CollectionChanged -= OnItemsSource_CollectionChanged;
    }

    // Now initialize with our new source.
    if (e.NewValue != null)
    {
        ((ObservableCollection<Node>)e.NewValue).CollectionChanged += OnItemsSource_CollectionChanged;
        control.DisplayInControl();
    }
}

private void OnItemsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    DisplayInControl();
}

Now, that said, the solution above is for a more generic case, where you might need to do something with the ItemsSource given to your custom control before passing it onto your MultiSelectCombo.ItemsSource. In your current case, however, you are simply building a collection of Node to exactly match the given collection of Node. If that's guaranteed to be the case, your solution can be much, much simpler:

private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var control = (MultiSelectComboBox)d;
    control.MultiSelectCombo.ItemsSource = (IEnumerable)e.NewValue;
}

Just let the wrapped ComboBox use the ItemsSource given to your custom control.