WPF Combobox initial dictionary binding value not showing - wpf

Question

I have a wpf combobox bound to a property LogicalP of a class SInstance. The ItemSource for the combobox is a dictionary that contains items of type LogicalP.
If I set LogicalP in SInstance to an initial state, the combobox text field shows empty. If I select the pulldown all my dictionary values are there. When I change the selection LogicalP in SInstance gets updated correctly. If I change Sinstance in C# the appropriate combobox value doesn't reflect the updated LogicalP from the pulldown.
I've set the binding mode to twoway with no luck. Any thoughts?
My Xaml:
<UserControl.Resources>
<ObjectDataProvider x:Key="PList"
ObjectType="{x:Type src:MainWindow}"
MethodName="GetLogPList"/>
</UserControl.Resources>
<DataTemplate DataType="{x:Type src:SInstance}">
<Grid>
<ComboBox ItemsSource="{Binding Source={StaticResource PList}}"
DisplayMemberPath ="Value.Name"
SelectedValuePath="Value"
SelectedValue="{Binding Path=LogicalP,Mode=TwoWay}">
</ComboBox>
</Grid>
</DataTemplate>
My C#:
public Dictionary<string, LogicalPType> LogPList { get; private set; }
public Dictionary<string, LogicalPType> GetLogPList()
{
return LogPList;
}
public class LogicalPType
{
public string Name { get; set; }
public string C { get; set; }
public string M { get; set; }
}
public class SInstance : INotifyPropertyChanged
{
private LogicalPType _LogicalP;
public string Name { get; set; }
public LogicalPType LogicalP
{
get { return _LogicalP; }
set
{
if (_LogicalP != value)
{
_LogicalP = value;
NotifyPropertyChanged("LogicalP");
}
}
}
#region INotifyPropertyChanged Members
#endregion
}

Answer 1

They are not looking at the same source.
You need to have SInstance supply both the LogPList and LogicalP.
_LogicalP is not connected to LogPList
If you want to different objects to compare to equal then you need to override Equals.

Answer 2

Here's my working solution. By moving the dictionary retrieval GetLogPList to the same class as that supplies the data (as suggested by Blam) I was able to get the binding to work both ways. I changed binding to a list rather than a dictionary to simplify the combobox
Here's the updated Xaml showing the new ItemsSource binding and removal of the SelectedValuePath:
<DataTemplate DataType="{x:Type src:SInstance}">
<Grid>
<ComboBox ItemsSource="{Binding GetLogPList}"
DisplayMemberPath ="Name"
SelectedValue="{Binding Path=LogicalP,Mode=TwoWay}">
</ComboBox>
</Grid>
</DataTemplate>
I then changed the dictionary LogPList to static so that it would be accessible to the class SInstance:
public static Dictionary<string, LogicalPType> LogPList { get; private set; }
Finally, I moved GetLogPList to the class SInstance as a property. Note again it's returning a list as opposed to a dictionary to make the Xaml a little simpler:
public class SInstance : INotifyPropertyChanged
{
public List<LogicalPType> GetLogPList
{
get { return MainWindow.LogPList.Values.ToList(); }
set { }
}
private LogicalPType _LogicalP;
public string Name { get; set; }
public LogicalPType LogicalP
{
get { return _LogicalP; }
set
{
if (_LogicalP != value)
{
_LogicalP = value;
NotifyPropertyChanged("LogicalP");
}
}
}
#region INotifyPropertyChanged Members
#endregion
}