Data Binding in Combobox - wpf

Question

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

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}" />

Answer 2

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 3

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.