Usercontrol in ListBox, binding in usercontrol doesn't work

Question

Everything happens in Windows Phone 7.1 Dev environment.

In my MainPage.xaml I have the ListBox:

<ListBox x:Name="LottoListBox" ItemsSource="{Binding lottoResults}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <Grid>
                <local:LottoResults Date="{Binding Date}" Results="{Binding Results}" />
            </Grid>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

As you can see, as ItemSource I set "lottoResults" collection.

public ObservableCollection<Lotto> lottoResults { get; set; }

"Lotto" class:

public DateTime Date
{
    get { return _date; }
    set
    {
        _date = value;
        NotifyPropertyChanged("Date");
    }
}
private DateTime _date;

public Structures.DoubleResult[] Results
{
    get { return _results; }
    set
    {
        _results = value;
        NotifyPropertyChanged("Results");
    }
}
private Structures.DoubleResult[] _results;

public event PropertyChangedEventHandler PropertyChanged;

private void NotifyPropertyChanged(string propertyName = "")
{
    if(PropertyChanged != null)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

DoubleResult structure contain two fields - int and bool, but it's not important right now because I didn't set any binding to "Results" field.

Let's look at my usercontrol "LottoResults":

public DateTime Date
{
    get { return (DateTime)GetValue(DateProperty); }
    set { SetValue(DateProperty, value); }
}

public static readonly DependencyProperty DateProperty =
    DependencyProperty.Register("Date", typeof(DateTime), typeof(LottoResults), new PropertyMetadata(new DateTime(), dateChanged));

public static void dateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    LottoResults control = d as LottoResults;
    MessageBox.Show("DateChanged!");
    // some magical, irrelevant voodoo which only I can understand. ;-)
}

And now some XAML, where I bind "Date" field.

<TextBlock Grid.ColumnSpan="6" Foreground="Black" FontSize="34" FontWeight="Bold" Text="{Binding Date, StringFormat='{}{0:yyyy.MM.dd}'}" />

And surprise, surprise - binding doesn't work! Well, in usercontrol it does. In DependencyProperty as a default value I set "new DateTime()", this is 0001.01.01 and exactly that is being displayed in the TextBlock.

In my lottoResults collection (ListBox's ItemsSource) I have 3 items (none of them has date "0001.01.01"). And ListBox displays 3 items, but a displayed date is always 0001.01.01. Even more, the "dateChanged()" method is never being executed (I get no MessageBox nor it stops on a breakpoint), so I guess that "Date" field never receives new value from binding.

But what is interesting, if I copy the code of TextBlock from usercontrol to the MainPage.xaml (so now it takes values directly from "lottoResults" collection) the binding does work!

<ListBox x:Name="LottoListBox" ItemsSource="{Binding lottoResults}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <Grid>
                <TextBlock Foreground="Black" FontSize="34" FontWeight="Bold" Text="{Binding Date, StringFormat='{}{0:yyyy.MM.dd}'}" />
            </Grid>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

So, why is that? I'm at the dead-end. I've spent half of a day to figure this out with no results.

Emond Erno Emond Erno · Accepted Answer · 2012-08-18T19:49:35

The Lotto class needs to implement INotifyPropertyChanged this will cause the UI/View to be signalled when a Lotto object property changes.

If the Results collection changes (items are added, removed) you'll need to use an ObservableCollection there too instead of an array.

Usercontrol in ListBox, binding in usercontrol doesn't work

1 Answers