i am trying to set selected item through following code but its not working:

```
<StackPanel Orientation="Horizontal">
                <TextBlock Text="Sort by" Margin="10" VerticalAlignment="Center"/>
                <ComboBox Width="{StaticResource ComboWidth}" x:Name="sortcombo" ItemsSource="{Binding Path=SortOrder}" SelectionChanged="SearchCombo_SelectionChanged" SelectedItem="{Binding Path=DefaultSortIndex}">
                    <ComboBox.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=Sort}"/>
                        </DataTemplate>
                    </ComboBox.ItemTemplate>
                </ComboBox>
            </StackPanel>

```

however it works fine if i use selectedIndex instead with binding to 0th index. Any thing wrong with declaration?