Binding Combobox SelectedValue to Page data value

BASE = C#, .Net, MVC, Silverlight 4 views

I've looked at responses to similar problems and I still can't get it to work. I guess it's not as simple a problem as I first thought.

I have a class AgreementInfo that contains, among other things, a ProjectProponent property

. . . 
public Responsible_Person ProjectProponent { get; set; }
. . . 

which is of type Responsible_Person

   . . .
   public string LASTNAME { get { return m_last; } set { m_last = value; } }
   public string USERNAME { get { return m_uname; } set { m_uname = value; } }
   public string FIRSTNAME { get { return m_first; } set { m_first = value; } }
   public string FullName { get { return m_first + " " + m_last; } }
   . . .

When the SL control loads it fetches, via json, an AgreementInfo object from the controller. This object is set as the DataContext for the LayoutRoot.

Then, I have a combobox whose ItemSource is set to a List. Currently, it is dummy data hard-wired in like

   . . .
   List<Responsible_Person> items = new List<Responsible_Person>();

   Responsible_Person newguy = new Responsible_Person();
   newguy.FIRSTNAME = "Jane"; newguy.LASTNAME = "Dough"; newguy.USERNAME = "jdough"; newguy.RP_ROLES = dummyroles;
   items.Add(newguy);
   . . . 

   cboProjectProponent.ItemsSource = items;
   cboProjectProponent.DisplayMemberPath = "FullName";

Eventually the list will be obtained from a service.

PROBLEM: In the XAML I have

. . .
<TextBlock x:Name="tbktest" Text="{Binding ProjectProponent.FullName}" />
<ComboBox x:Name="cboProjectProponent" SelectedValue="{Binding ProjectProponent.FullName, Mode=TwoWay}" />
. . . 

I am guessing that I see the correct name from AgreementInfo in the text block but the same name, which does appear in the drop-down list, is not selected beca开发者_JAVA百科use I am binding to the wrong thing. What I want is the combobox loaded with values from the List and the ProjectProponent from the AgreementInfo to be the selected item.

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Is your ItemSource set before the binding? If the binding occurs before the ItemSource is set then the SelectedValue binding will not work. I have seen these types of timing issues before. Can you not set the ItemSource via XAML binding rather than in code?

I notice you are also not setting the SelectedValuePath property of the combo. Without this you are attempting to assign a Responsible_Person to ProjectProponent.FullName (the SelectedValue). Check this article out for a good explanation of all the ComboBox control properties: http://johnpapa.net/binding-to-silverlight-combobox-and-using-selectedvalue-selectedvaluepath-and-displaymemberpath