ComboBox.SelectedValue not updating from binding source
binding, combobox, data-binding, wpf
Solution
We had a similar issue last week. It has to do with how `SelectedValue` updates its internals. What we found was if you set `SelectedValue` it would not see the change we had to instead set `SelectedItem` which would properly update every thing. My conclusion is that `SelectedValue` is designed for get operations and not set. But this may just be a bug in the current version of 3.5sp1 .net
Problem
Here's my binding source object: ``` Public Class MyListObject Private _mylist As New ObservableCollection(Of String) Private _selectedName As String Public Sub New(ByVal nameList As List(Of String), ByVal defaultName As String) For Each name In nameList _mylist.Add(name) Next _selectedName = defaultName End Sub Public ReadOnly Property MyList() As ObservableCollection(Of String) Get Return _mylist End Get End Property Public ReadOnly Property SelectedName() As String Get Return _selectedName End Get End Property End Class ``` Here is my XAML: ``` <Window x:Class="Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300" xmlns:local="clr-namespace:WpfApplication1" > <Window.Resources> <ObjectDataProvider x:Key="MyListObject" ObjectInstance="" /> </Window.Resources> <Grid> <ComboBox Height="23" Margin="24,91,53,0" Name="ComboBox1" VerticalAlignment="Top" SelectedValue="{Binding Path=SelectedName, Source={StaticResource MyListObject}, Mode=OneWay}" ItemsSource="{Binding Path=MyList, Source={StaticResource MyListObject}, Mode=OneWay}" /> <Button Height="23" HorizontalAlignment="Left" Margin="47,0,0,87" Name="btn_List1" VerticalAlignment="Bottom" Width="75">List 1</Button> <Button Height="23" Margin="0,0,75,87" Name="btn_List2" VerticalAlignment="Bottom" HorizontalAlignment="Right" Width="75">List 2</Button> </Grid> </Window> ``` Here's the code-behind: ``` Class Window1 Private obj1 As MyListObject Private obj2 As MyListObject Private odp As ObjectDataProvider Public Sub New() InitializeComponent() Dim namelist1 As New List(Of String) namelist1.Add("Joe") namelist1.Add("Steve") obj1 = New MyListObject(namelist1, "Steve") . Dim namelist2 As New List(Of String) namelist2.Add("Bob") namelist2.Add("Tim") obj2 = New MyListObject(namelist2, "Tim") odp = DirectCast(Me.FindResource("MyListObject"), ObjectDataProvider) odp.ObjectInstance = obj1 End Sub Private Sub btn_List1_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btn_List1.Click odp.ObjectInstance = obj1 End Sub Private Sub btn_List2_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btn_List2.Click odp.ObjectInstance = obj2 End Sub End Class ``` When the Window first loads, the bindings hook up fine. The ComboBox contains the names "Joe" and "Steve" and "Steve" is selected by default. However, when I click a button to switch the ObjectInstance to obj2, the ComboBox ItemsSource gets populated correctly in the dropdown, but the SelectedValue is set to Nothing instead of being equal to obj2.SelectedName.