Wpf Combobox with databinding: initial value is empty - wpf

Question

In the following xaml fragment SessoList is a list of string ("M" and "F").
<ComboBox IsEditable="False" Margin="5" SelectedValue="{Binding Sesso}" ItemsSource="{Binding SessoList}" Width="40" Height="28"/>
The combobox works as expected and it is pre-populated reflecting the value of Sesso in the viewmodel.
The combobox selectable items are only two and fixed so I tried to simplify defining them in xaml:
<ComboBox IsEditable="False" Margin="5" SelectedValue="{Binding Sesso}" SelectedValuePath="{Binding Tag}" Width="40" Height="28" Name="Primo">
<ComboBoxItem Content="M" Tag="M" />
<ComboBoxItem Content="F" Tag="F" />
</ComboBox>
This combobox is capable of updating the viewmodel property sesso, but is not pre-populated with the correct value.
The following error is reported:
BindingExpression path error: 'Tag' property not found on 'object'
How can I successfully define the combobox items in xaml and have it display the right value based on SelectedValue databinding ?
Forgot to mention I'm using .Net 4.0

Answer 1

As I can understand, you want to define the ComboBox ItemsSource in XAML,
here is the solution that worked for me:
Xaml Window resources:
<Window.Resources>
<x:Array x:Key="Array" Type="{x:Type nirHelpingOvalButton:ComboObjectModel}">
<nirHelpingOvalButton:ComboObjectModel Content="M_Content" Tag="M_Tag"/>
<nirHelpingOvalButton:ComboObjectModel Content="F_Content" Tag="F_Tag"/>
</x:Array>
Xaml Combo:
<Grid>
<ComboBox IsSynchronizedWithCurrentItem="True" IsEditable="False" SelectedIndex="0" Margin="5" ItemsSource="{StaticResource Array}"
SelectedValue="{Binding Content, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
SelectedValuePath="Tag" Width="90" Height="28" Name="Primo">
<i:Interaction.Behaviors>
<nirHelpingOvalButton:CustomComboSelectionBehavior/>
</i:Interaction.Behaviors>
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Content}"></TextBlock>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox></Grid>
View model combo SelectedValue binded property:
public string Content
{
get { return _content; }
set
{
_content = value;
OnPropertyChanged("Content");
}
}
List item Behavior Code:
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.Loaded += OnLoaded;
}
private void OnLoaded(object sender, RoutedEventArgs e)
{
var firstItem = AssociatedObject.ItemsSource.Cast<object>().FirstOrDefault();
AssociatedObject.SelectedItem = firstItem;
}
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.Loaded -= OnLoaded;
}
regards