WPF: Binding to single complex item

Question

Hi there,

In my application, I use a UserControl instance to display the contents of a complex type that implements INotifyPropertyChanged that is a ViewModel to display the current state of background processes. This ViewModel is exposed to the UserControl as a DependencyProperty.

The DependencyProperty is being set nicely, and events are happily sent out by the ViewModel. However, it seems that WPF's data binding is giving me a slight headache. (Plus, I wouldn't count myself as an expert on WPF; the problem and its solution may be simple, but it's eluding me.)

Basically, all I see is "Initialzing" on my UI, which is the DependencyProperty's default value, and the fallback value used for binding. If I alter the DependencyProperty's default value, the UI shows these values instead. If I remove the DependencyProperty's default value (ie. null), it uses the fallback values.

What I actually wanted is to display the ViewModel's contents.

---

View model:

public class ImportInformation : INotifyPropertyChanged
{
     /* ... */
}

User control:

public partial class ImportTab : UserControl
{
    public static readonly DependencyProperty ValueProperty = DependencyProperty
        .Register("ValueProperty", typeof(ImportInformation), typeof(ImportTab), new PropertyMetadata(new ImportInformation { TaskName = "Initializing...", CurrentTask = "Initializing...", Progress = Double.NaN }));

    public ImportInformation Value
    {
        get { return (ImportInformation)GetValue(ValueProperty); }
        set { SetValue(ValueProperty, value); }
    }

    public ImportTab()
    {
        InitializeComponent();
    }
}

XAML:

<UserControl x:Class="LingImp.Tabs.ImportTab"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:conv="clr-namespace:LingImp.Converters"
             mc:Ignorable="d" Name="root"
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <conv:NaNConverter x:Key="nanConv"/>
    </UserControl.Resources>
    <StackPanel Orientation="Vertical">
        <TextBlock Padding="0,4,0,4" TextWrapping="Wrap">
            Your import is currently being processed. Depending on the data source, this can take a long, <Italic>long</Italic> time.
        </TextBlock>
        <GroupBox VerticalAlignment="Top" HorizontalAlignment="Left" MinWidth="150" DataContext="{Binding ElementName=root, Path=Value}">
            <GroupBox.Header>
                <TextBlock FontWeight="Bold" Text="{Binding Path=TaskName, Mode=OneWay, FallbackValue=Initializing...}"/>
            </GroupBox.Header>
            <StackPanel Orientation="Vertical" Margin="4">
                <TextBlock TextWrapping="Wrap" Text="{Binding Path=CurrentTask, Mode=OneWay, FallbackValue=Initializing...}"
                           Margin="0,0,0,2"/>
                <ProgressBar MinHeight="9" HorizontalAlignment="Stretch" Minimum="0" Maximum="1"
                             IsIndeterminate="{Binding Path=Progress, Mode=OneWay, FallbackValue=true, Converter={StaticResource nanConv}}"
                             Value="{Binding ElementName=root, Path=Value.Progress, Mode=OneWay, FallbackValue=0}"/>
                <TextBlock FontSize="11" HorizontalAlignment="Right"
                           Text="{Binding Path=Progress, Mode=OneWay, FallbackValue=0, StringFormat=\{0:P\}}"/>
            </StackPanel>
        </GroupBox>
    </StackPanel>
</UserControl>

Answer 1

My bad. I registered the DependencyProperty wrong:

    public static readonly DependencyProperty ValueProperty = DependencyProperty
        .Register("ValueProperty", typeof(ImportInformation), typeof(ImportTab));

...should have read...

    public static readonly DependencyProperty ValueProperty = DependencyProperty
        .Register("Value", typeof(ImportInformation), typeof(ImportTab));

That, of course, fixed it. Thanks anyhow :-)

Answer 2

public static readonly DependencyProperty ValueProperty = DependencyProperty    
        .Register("Value", ...);    
...
<TextBlock 
  ... 
  Text="{Binding ElementName=root, ...}"/>
  ...