wpf combobox default value to textBlock - wpf

Question

I need to add a default value 'select' in the combobox.I cant add this value to the database.This location value is dynamic.It appears based upon the userrole. I tried different ways nothing worked.Please help.
<ComboBox Width="140" ItemsSource="{Binding SecurityContexts, Mode=OneWay}"
SelectedItem="{Binding ActiveSecurityContext, Mode=TwoWay}"
ToolTip="Working Location">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Location}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
The code behind is
SecurityContexts = new ObservableCollection(_currentUser.ApplicationSecurityContexts);
public interface IApplicationSecurityContext
{
IRole Role { get; }
string Location { get; }
IEnumerable<string> Budgets { get; }
}
public IApplicationSecurityContext ActiveSecurityContext
{
get { return this._currentUser.ActiveSecurityContext; }
set
{
if (this._currentUser.ActiveSecurityContext != value)
{
this._currentUser.ChangeActiveSecurityContext(value);
RaisePropertyChanged("CurrentUser");
LoadData();
}
}
}

Answer 1

You can achieve your goal using CompositeCollection
you can do this. Define resource in your grid/usercontrol/combobox:
<Grid.Resources>
<CollectionViewSource x:Key="cvs" Source="{Binding Binding SecurityContexts, Mode=OneWay}" />
<DataTemplate DataType="{x:Type c:SecurityContexts}">
<TextBlock Text="{Binding Location}"/>
</DataTemplate>
</Grid.Resources>
then your combobox itemsource will be:
<ComboBox.ItemsSource>
<CompositeCollection>
<ComboBoxItem>
<TextBlock Text="select"/>
</ComboBoxItem>
<CollectionContainer Collection="{Binding Source= {StaticResource cvs}}"/>
</CompositeCollection>
</ComboBox.ItemsSource>
It should work. You need to define your datatemplate for your collection in the resource too, to define how your item will be displayed
Note that c in c:SecurityContexts is the path where you defined your custom object