Exception when Data Binding ListBox

Question

I am implementing an application in MVVM. Right now I am trying to create an autocomplete that queries a database for potential results. The issue I am having right now is that when I try to set the Collection Property for the Listbox, I get this exception:

  System.Windows.Markup.XamlParseException occurred
  HResult=0x80131501
  Message=A 'Binding' cannot be set on the 'Path' property of type 'Binding'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.
  Source=<Cannot evaluate the exception source>

Here is my implementation:

XAML

<Border Margin="5,2,5,5" Grid.Row="1" Height="Auto"
                    BorderBrush="DarkBlue"
                    BorderThickness="1" CornerRadius="4">
    <ScrollViewer VerticalScrollBarVisibility="Auto" MaxHeight="40">
        <DockPanel x:Name="DockPanelA" Margin="1,1,1,1" Background="White" Height="Auto">
            ....
            <TextBox x:Name="TextBoxA" Background="{x:Null}" 
                     BorderThickness="0" Width="Auto"
                     CaretBrush="SteelBlue" FontSize="14" Foreground="SteelBlue" FontFamily="Calibri" TextAlignment="Left"
                     TextChanged="TextBoxA_TextChanged"/>
        </DockPanel>
    </ScrollViewer>
</Border>
<ListBox Grid.Row="1" Margin="5,2,5,5" MaxHeight="200" Width="{Binding ActualWidth, ElementName=DockPanelA}"
             ScrollViewer.VerticalScrollBarVisibility="Auto"  HorizontalAlignment="Stretch"
             Background="AliceBlue" BorderBrush="DarkBlue" Foreground="SteelBlue" VirtualizingStackPanel.IsVirtualizing="False"
             ItemsSource="{Binding Path=MyCollection, Mode=TwoWay}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock>
                <TextBlock.Text>
                    <MultiBinding StringFormat="{}{0} {1}">
                        <Binding Path="{Binding Symbol}"/>
                        <Binding Path="{Binding Name}"/>
                    </MultiBinding>
                </TextBlock.Text>
            </TextBlock>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

C# ViewModel

public class ViewModel : INotifyPropertyChanged
{
    private ObservableCollection<ListData> _myListItems;

    ...
    public ObservableCollection<ListData> MyListItems
    {
        get { return _myListItems; }
        set { _myListItems = value; NotifyPropertyChanged("MyListItems"); }
    }
    ...

    protected virtual void NotifyPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
        {
            var e = new PropertyChangedEventArgs(propertyName);
            handler(this, e);
        }
    }
    ...
    public void DataSearch(object param)
    {
        ...
        Task t = Task.Run(async () =>
        {
            await Task.Delay(5000);
            try
            {
                currSrc.Token.ThrowIfCancellationRequested();
                IList<ListData> newList = Helper.QueryData(searchString);
                currSrc.Token.ThrowIfCancellationRequested();

                MyListItems = new ObservableCollection<ListData>(newList);
                //Exception is Thrown from this
            }
            catch (Exception e)
            {
            }
        });
        ...
    }
    ...
}
public class InputHandler : ICommand
{
    //View calls this and this calls DataSearch as a result
}

I've been trying to figure out why this is happening since other properties that I've databinded this way work properly. Does anyone know why this exception is thrown and how to fix it?

The error message is pretty clear. Replace <Binding Path="{Binding Symbol}"/> by <Binding Path="Symbol"/>. Besides that, you bind the ListBox's ItemsSource to MyCollection, while the view model property seems to be MyListItems. Note also that setting Mode=TwoWay on the ItemsSource binding is pointless. — Clemens
– Clemens, Commented May 11, 2017 at 16:21

mvermef · Accepted Answer · 2017-05-11 16:23:36Z

1

<ListBox.ItemTemplate>
    <DataTemplate>
        <TextBlock>
            <TextBlock.Text>
                <MultiBinding StringFormat="{}{0} {1}">
                    <Binding Path="Symbol"/>
                    <Binding Path="Name"/>
                </MultiBinding>
            </TextBlock.Text>
        </TextBlock>
    </DataTemplate>
</ListBox.ItemTemplate>

answered May 11, 2017 at 16:23

mvermef

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1 Comment

Informat Over a year ago

Thank-you guys so much, I can't believe i missed that.

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