<UserControl x:Class="WpfApplication5.View"\n    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"\n    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">\n    <StackPanel>\n        <ComboBox ItemsSource="{Binding Path=Items, Mode=OneTime}" SelectedValue="{Binding Path=SelectedItem}"/>\n        <TextBox Text="{Binding Path=SomeProperty}"/>\n    </StackPanel>\n</UserControl>

public class ViewModel : INotifyPropertyChanged\n{\n    public event PropertyChangedEventHandler PropertyChanged;\n    private void InvokePropertyChanged(String propertyName)\n    {\n        PropertyChangedEventHandler propertyChanged = PropertyChanged;\n        if (propertyChanged != null) propertyChanged(this, new PropertyChangedEventArgs(propertyName));\n    }\n\n    public IEnumerable<String> Items { get; private set; }\n    private string _selectedItem;\n    public String SelectedItem\n    {\n        get { return _selectedItem; }\n        set\n        {\n            if (_selectedItem == value) return;\n\n            _selectedItem = value;\n            InvokePropertyChanged("SelectedItem");\n\n            Console.WriteLine("SelectedItem: " + (value ?? "null"));\n        }\n    }\n\n    private string _someProperty;\n    public String SomeProperty\n    {\n        get { return _someProperty; }\n        set\n        {\n            if (_someProperty == value) return;\n\n            _someProperty = value;\n            InvokePropertyChanged("SomeProperty");\n\n            Console.WriteLine("SomeProperty: " + (value ?? "null"));\n        }\n    }\n\n    public ViewModel()\n    {\n        Items = new List<string> {"aaaa", "bbbb", "cccc", "dddd"};\n        SelectedItem = "aaaa";\n    }\n}

<Window x:Class="WpfApplication5.Window1"\n    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"\n    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"\n    Title="Window1" Height="300" Width="300">\n    <StackPanel>\n        <ContentControl Name="ContentControl1" Height="100" />\n        <Button Content="Load" Click="Load"/>\n        <Button Content="Unload" Click="Unload"/>\n    </StackPanel>\n</Window>

public partial class Window1 : Window\n{\n    public Window1()\n    {\n        InitializeComponent();\n    }\n\n    private void Load(object sender, RoutedEventArgs e)\n    {\n        ContentControl1.Content = new View {DataContext = new ViewModel()};\n    }\n\n    private void Unload(object sender, RoutedEventArgs e)\n    {\n        var view = ContentControl1.Content as FrameworkElement;\n        // При исполнении следующей строчки идёт обнуление св-ва SelectedItem у вьюмодели\n        if(view!=null) view.DataContext = null;\n        ContentControl1.Content = null;\n    }\n}