DependencyProperty for ItemsSource

Question

I have a XAML like:

<UserControl x:Class="Book.CustomControls.HeaderedComboBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             DataContext="{Binding RelativeSource={RelativeSource Self}}"
             Width="200" Height="50">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <TextBlock Grid.Row="0" Margin="2,2" VerticalAlignment="Center" Text="{Binding Header}" FontWeight="{Binding HeaderFontWeight}"/>
        <ComboBox Grid.Row="1" Margin="2,2" VerticalAlignment="Center" ItemsSource="{Binding ItemsSource, UpdateSourceTrigger=PropertyChanged}"
                  SelectedItem="{Binding SelectedItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
    </Grid>
</UserControl>

The cs-file therefor is:

public partial class HeaderedComboBox : UserControl
{
    public HeaderedComboBox()
    {
        this.InitializeComponent();
        this.HeaderFontWeight = FontWeights.Normal;
    }

    public static readonly DependencyProperty HeaderProperty = DependencyProperty.Register("Header", typeof(string), typeof(HeaderedComboBox));
    public static readonly DependencyProperty HeaderFontWeightProperty = DependencyProperty.Register("HeaderFontWeight", typeof(FontWeight), typeof(HeaderedComboBox));
    public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.Register("ItemsSource", typeof(IEnumerable), typeof(HeaderedComboBox));
    public static readonly DependencyProperty SelectedItemProperty = DependencyProperty.Register("SelectedItem", typeof(object), typeof(HeaderedComboBox));

    public string Header
    {
        get { return (string)GetValue(HeaderProperty); }
        set { SetValue(HeaderProperty, value); }
    }

    public FontWeight HeaderFontWeight
    {
        get { return (FontWeight)GetValue(HeaderFontWeightProperty); }
        set { SetValue(HeaderFontWeightProperty, value); }
    }

    public IEnumerable ItemsSource
    {
        get { return (IEnumerable)GetValue(ItemsSourceProperty); }
        set { SetValue(ItemsSourceProperty, value); }
    }

    public object SelectedItem
    {
        get { return GetValue(SelectedItemProperty); }
        set { SetValue(SelectedItemProperty, value); }
    }
}

I tried to use this UserControl in any Window with

<customControls:HeaderedComboBox Header="Category" ItemsSource="{Binding Categories}"/>

Categories is just an ObservableCollection<string>.

Unfortunately I don't see any items in the ComboBox. At the moment I have no idea, what I'm doing wrong. Any ideas?

Answer 1

System.Windows.Data Error: 40 : BindingExpression path error: 'Categories' property not found on 'object' ''HeaderedComboBox' (Name='')'. BindingExpression:Path=Categories; DataItem='HeaderedComboBox' (Name=''); target element is 'HeaderedComboBox' (Name=''); target property is 'ItemsSource' (type 'IEnumerable')

Your DataContext is set to HeaderedCombobox and there system is looking for a Categories. Property Header worked since you put a text into it without binding. Possible solution

<Window x:Class="WpfApplication5.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525"
    xmlns:local="clr-namespace:WpfApplication5" Name="window">
<Grid>
    <local:HeaderedComboBox Header="Category" ItemsSource="{Binding ElementName=window, Path=DataContext.Categories}"/>
</Grid>