Data Binding in Combobox

Question

Hi, I binded a database table's primary key to the selectedIndex of a combobox. the problem occurs where the primary key starts from 1 but selectedIndex accepts from 0. I mean, when I want to see the item with ID=1 in database, since it's listed as first element in combobox with index 0, it displays the second element in the list, which is considered with ID=1 in the combobox. Can anyone help me on solving this problem?

Thanks in advance. here's my combobox:

<ComboBox SelectedIndex="{Binding SC.User1.UserID, UpdateSourceTrigger=PropertyChanged }" IsSynchronizedWithCurrentItem="True"
 x:Name="proxyResponsibleUserCmb" ItemsSource="{Binding Users, Mode=OneTime}"
 SelectedItem="{Binding SC.User1.FullName, ValidatesOnDataErrors=True,  UpdateSourceTrigger=PropertyChanged}"
Validation.ErrorTemplate="{x:Null}"  Height="23" VerticalAlignment="Top" HorizontalAlignment="Left" Width="118" Margin="184,3,0,0" Grid.Row="0" Grid.Column="1"/>

Answer 1

Does setting the property IsSynchronizedWithCurrentItem (in your XAML) to True help?

EDIT Maybe this link will help:

http://social.msdn.microsoft.com/Forums/en/wpf/thread/b4e84ea2-9597-4af1-8d3c-835b972e3d73

Answer 2

Quick workaround via a ValueConverter:

Create a ValueConverter in your codebehind:

// of course use your own namespace...
namespace MyNameSpace
{
public class IndexConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if(!(value is int)) // Add the breakpoint here!!
            throw new Exception();
        int newindex = ((int)value - 1;
        return newindex;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException("This method should never be called");
    }
}
}

Then, make it known in your XAML:

//(declare a namespace in your window tag:)
xmlns:myNamespace="clr-namespace:MyNameSpace"

// add:
<Window.Resources>
    <ResourceDictionary>
        <myNamespace:IndexConverter x:Key="indexConverter" />
    </ResourceDictionary>
</Window.Resources>

Then change your binding:

<ComboBox SelectedIndex="{Binding SC.User1.UserID, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource indexConverter}}" ... />

That should do the trick. At least you can debug it by inserting a breakpoint in the IndexConverter.

Answer 3

What about using the ComboBox's SelectedValuePath and DisplayMemberPath, and setting your default item with SelectedValue instead of SelectedItem?

<ComboBox x:Name="proxyResponsibleUserCmb" 
    SelectedValuePath="{Binding UserID}" 
    DisplayMemberPath="{Binding FullName}"
    SelectedValue="{Binding SC.User1.UserId, ValidatesOnDataErrors=True,  UpdateSourceTrigger=PropertyChanged}" 
    ItemsSource="{Binding Users, Mode=OneTime}" />