Silverlight Combobox - Setting the SelectedItem MVVM - silverlight

Question

I have a ViewModel that sets the value for the "UserStructure" property. The problem is that the combobox wont bind to the value.
public class OwnerOccupierAccountViewModel : ViewModelBase
{
/// <summary>
/// Load combobox structures
/// </summary>
private readonly LoadOperation<Structure> _loadStructures;
private readonly LoadOperation<UnitOccupierDetail> _loadUnitOccupierDetails;
//public ICommand SaveAccountSettingsCommand { get; set; }
#region Properties
private ObservableCollection<Structure> _structures;
public ObservableCollection<Structure> Structures
{
get { return _structures; }
set
{
_structures = value;
RaisePropertyChanged("Structures");
}
}
private Structure _userStructure;
public Structure UserStructure
{
get { return _userStructure; }
set
{
_userStructure = value;
RaisePropertyChanged("SelectedStructure");
}
}
private UnitOccupierDetail _unitOccupierDetail;
public UnitOccupierDetail UnitOccupierDetail
{
get { return _unitOccupierDetail; }
set
{
_unitOccupierDetail = value;
RaisePropertyChanged("UnitOccupierDetail");
}
}
#endregion
public OwnerOccupierAccountViewModel()
{
// SaveAccountSettingsCommand = new DelegateCommand(SaveAccountSettings, CanSave);
UserAccountContext _userAccountContext;
if (!DesignerProperties.IsInDesignTool)
{
var loggedInUser = new Guid(WebContext.Current.User.UserID.ToString());
_userAccountContext = new UserAccountContext();
#region load structures
_loadStructures = _userAccountContext.Load(_userAccountContext.GetStructuresQuery());
_loadStructures.Completed += _loadStructuresCompleted;
#endregion
#region load user data
_loadUnitOccupierDetails =
_userAccountContext.Load(
_userAccountContext.GetUnitOccupierDetailsQuery().Where(
u => u.UserIDFK == loggedInUser && u.StructureFK == 92));
_loadUnitOccupierDetails.Completed += _loadUnitOccupierDetails_Completed;
#endregion
}
}
void _loadUnitOccupierDetails_Completed(object sender, EventArgs e)
{
_unitOccupierDetail= new UnitOccupierDetail();
_unitOccupierDetail = _loadUnitOccupierDetails.Entities.First();
_userStructure = _unitOccupierDetail.Structure;
}
void _loadStructuresCompleted(object sender, EventArgs e)
{
var theseStructures = new ObservableCollection<Structure>(_loadStructures.Entities);
Structures = theseStructures;
}
//private void SaveAccountSettings(object param)
//{
//}
//private static bool CanSave(object param)
//{
// return true;
//}
}
<ComboBox x:Name="cboApartments"
ItemsSource='{Binding Structures, Mode=TwoWay}'
DisplayMemberPath='StructureName'
SelectedValuePath='IDStructure'
SelectedItem='{Binding SelectedStructure,Mode=TwoWay}'
Width="200"
Height="25">

Answer 1

in xaml UserStructure instead SelectedStructure.

Answer 2

In your XAML SelectedItem is bound to SelectedStructure instead of UserStructure what you want
UPDATE:
Your code doesn't work because you should set to SelectedItem object that has reference equality with some object in ItemsSource. In your ViewModel you set Structures as result of one service operation and UserStructure as result of the other. UserStructure and some object in Structures can be equals (object.Equals) but not reference equals (object.ReferenceEquals). ComboBox like other ItemsControls doesn't compare items by equality, it compares they by identity. So, to have right code you should select from Structures object that equals to UserStructure and set it as UserStructure:
void _loadUnitOccupierDetails_Completed(object sender, EventArgs e)
{
...
Structure userStructure = Structures.FirstOrDefault(s=>s.Equals(_unitOccupierDetail.Structure));
UserStructure = userStructure;
}
In this case you should be sure that Structures comes before. You can look at Reactive Extensions Observable.ForkJoin() method to syncronize 2 async calls.

Answer 3

Try such changes
public class OwnerOccupierAccountViewModel : ViewModelBase
{
/// <summary>
/// Load combobox structures
/// </summary>
private readonly LoadOperation<Structure> _loadStructures;
private readonly LoadOperation<UnitOccupierDetail> _loadUnitOccupierDetails;
//public ICommand SaveAccountSettingsCommand { get; set; }
#region Properties
private ObservableCollection<Structure> _structures;
public ObservableCollection<Structure> Structures
{
get { return _structures; }
set
{
_structures = value;
RaisePropertyChanged("Structures");
}
}
private Structure _userStructure;
public Structure UserStructure
{
get { return _userStructure; }
set
{
_userStructure = value;
RaisePropertyChanged("UserStructure");
}
}
private UnitOccupierDetail _unitOccupierDetail;
public UnitOccupierDetail UnitOccupierDetail
{
get { return _unitOccupierDetail; }
set
{
_unitOccupierDetail = value;
RaisePropertyChanged("UnitOccupierDetail");
}
}
#endregion
public OwnerOccupierAccountViewModel()
{
// SaveAccountSettingsCommand = new DelegateCommand(SaveAccountSettings, CanSave);
UserAccountContext _userAccountContext;
if (!DesignerProperties.IsInDesignTool)
{
var loggedInUser = new Guid(WebContext.Current.User.UserID.ToString());
_userAccountContext = new UserAccountContext();
#region load structures
_loadStructures = _userAccountContext.Load(_userAccountContext.GetStructuresQuery());
_loadStructures.Completed += _loadStructuresCompleted;
#endregion
#region load user data
_loadUnitOccupierDetails =
_userAccountContext.Load(
_userAccountContext.GetUnitOccupierDetailsQuery().Where(
u => u.UserIDFK == loggedInUser && u.StructureFK == 92));
_loadUnitOccupierDetails.Completed += _loadUnitOccupierDetails_Completed;
#endregion
}
}
void _loadUnitOccupierDetails_Completed(object sender, EventArgs e)
{
_unitOccupierDetail= new UnitOccupierDetail();
_unitOccupierDetail = _loadUnitOccupierDetails.Entities.First();
_userStructure = _unitOccupierDetail.Structure;
}
void _loadStructuresCompleted(object sender, EventArgs e)
{
var theseStructures = new ObservableCollection<Structure>(_loadStructures.Entities);
Structures = theseStructures;
}
//private void SaveAccountSettings(object param)
//{
//}
//private static bool CanSave(object param)
//{
// return true;
//}
}
<ComboBox x:Name="cboApartments"
ItemsSource='{Binding Structures, Mode=TwoWay}'
DisplayMemberPath='StructureName'
SelectedValuePath='IDStructure'
SelectedItem='{Binding UserStructure,Mode=TwoWay}'
Width="200"
Height="25">
Updated:
Hmm, maybe try changes here:
<ComboBox x:Name="cboApartments"
ItemsSource='{Binding Structures, Mode=TwoWay}'
SelectedItem='{Binding UserStructure, Mode=TwoWay}'
Width="200"
Height="25">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=StructureName}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>