wpf databinding combobox within treeview - wpf

Question

I am very new to WPF, and help appreciated:
Model:
Collection<Presenter>,
Presenter has a Collection<Presentation>,
Presentation has a TeachingSession property (which contains a DateTime? property)
I am trying to have a treeview display:
presenter name
[combobox of available Dates]
At the moment, each presenter name in the treeview is displaying correctly, and the first parent item expanded displays the combobox with the correctly selected date. However, comboboxes displaying at any one time are all 'in sync' - that is changing the value in a combobox (or expanding a different treeview item) changes the value for all comboboxes which can be seen, so they all display the same date.
<TreeView Name="PresenterTreeView" ItemsSource="{Binding}">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Presenter}"
ItemsSource="{Binding Path=Presentations}">
<TextBlock Text="{Binding Path=FullName}" />
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:Presentation}">
<ComboBox SelectedItem="{Binding Path=TeachingSession, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
DisplayMemberPath="SessionDate"
ItemsSource="{Binding Source={StaticResource availableDatesViewSource}}" >
</ComboBox>
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>

Answer 1

I have compliled your example and I cant get the comboboxes to sync like you are describing.
Perhaps you will be able to see what I done different and it might be the fix, Or maybe I am just wrong and am missing somthing from your question?
This is the code I used:
Xaml:
<Window x:Class="WpfApplication8.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="340" Width="480" Name="UI" xmlns:local="clr-namespace:WpfApplication8">
<TreeView Name="PresenterTreeView" DataContext="{Binding ElementName=UI}" ItemsSource="{Binding Path=Presenters}" >
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Presenter}" ItemsSource="{Binding Path=Presentations}">
<TextBlock Text="{Binding FullName}" />
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:Presentation}">
<ComboBox SelectedItem="{Binding TeachingSession.SessionDate}" ItemsSource="{Binding ElementName=UI, Path=Dates}" />
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
</Window>
Code:
public partial class MainWindow : Window
{
private ObservableCollection<Presenter> _myProperty = new ObservableCollection<Presenter>();
private ObservableCollection<DateTime?> _myDates = new ObservableCollection<DateTime?>();
public MainWindow()
{
InitializeComponent();
DateTime time1 = DateTime.Now;
DateTime time2 = DateTime.Now.AddDays(1);
Dates.Add(time1);
Dates.Add(time2);
for (int i = 0; i < 20; i++)
{
Dates.Add(DateTime.Now.AddDays(i));
}
TeachingSession teach = new TeachingSession { SessionDate = time1 };
Presentation pres = new Presentation { TeachingSession = teach };
Presenter presenter = new Presenter { FullName = "Presenter1" };
presenter.Presentations = new ObservableCollection<Presentation>();
presenter.Presentations.Add(pres);
TeachingSession teach1 = new TeachingSession { SessionDate = time2 };
Presentation pres1 = new Presentation { TeachingSession = teach1 };
Presenter presenter1 = new Presenter { FullName = "Presenter1" };
presenter1.Presentations = new ObservableCollection<Presentation>();
presenter1.Presentations.Add(pres1);
Presenters.Add(presenter);
Presenters.Add(presenter1);
}
public ObservableCollection<Presenter> Presenters
{
get { return _myProperty; }
set { _myProperty = value; }
}
public ObservableCollection<DateTime?> Dates
{
get { return _myDates; }
set { _myDates = value; }
}
}
public class Presenter
{
public string FullName { get; set; }
public ObservableCollection<Presentation> Presentations { get; set; }
}
public class Presentation
{
public TeachingSession TeachingSession { get; set; }
}
public class TeachingSession
{
public DateTime? SessionDate { get; set; }
}
Result:

Answer 2

Because of sa_ddam213's answer, i was able to track the problem down to the default synchronisation with the CollectionViewSource used to bindItemsSource
The combobox needed the attribute:
IsSynchronizedWithCurrentItem="False"