WPF

private void ApplyTheme()
{
    ResourceDictionary resources = null;
    string fileName = string.Empty;

    switch (SelectedThemeName)
    {
        case "Black":
            fileName = "Theme_Black.xaml";
            break;

        case "Blue":
            fileName = "Theme_Blue.xaml";
            break;

    }

    if (fileName == string.Empty)
    {
        throw new Exception(string.Format("Resource dictionary for theme name {0} not found", SelectedThemeName));
    }

    fileName = "..\Themes\" + fileName;

    if (!File.Exists(fileName))
    {
        throw new Exception(string.Format("Theme name {0} not found", SelectedThemeName));
    }

    using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read))
    {
        resources = (ResourceDictionary)XamlReader.Load(fs);
    }
    Application.Current.Resources = resources;
}

<ListView x:Name="listviewReaders" ItemsSource="{Binding ReadersList, UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" SelectedItem="{Binding SelectedReader, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Width="160" Margin="25,23,315,40">
       <ListView.ItemTemplate>
           <DataTemplate>
               <TextBlock Text="{Binding FullName}" />
           </DataTemplate>
       </ListView.ItemTemplate>
   </ListView>

    <Grid>
    <TextBox x:Name="txtBxFullName" HorizontalAlignment="Left" Height="23" Margin="25,27,0,0" TextWrapping="Wrap" Text="{Binding CurrentReader.FullName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
    <TextBox x:Name="txtBxSerialNumber" HorizontalAlignment="Left" Height="23" Margin="25,55,0,0" TextWrapping="Wrap" Text="{Binding CurrentReader.SerialNumber, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
    <TextBox x:Name="txtBxIdNumber" HorizontalAlignment="Left" Height="23" Margin="25,83,0,0" TextWrapping="Wrap" Text="{Binding CurrentReader.IdNumber, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
    <TextBox x:Name="txtBxAdress" HorizontalAlignment="Left" Height="23" Margin="25,111,0,0" TextWrapping="Wrap" Text="{Binding CurrentReader.Adress, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
    <TextBox x:Name="txtBxAltContactMethods" HorizontalAlignment="Left" Height="23" Margin="25,139,0,0" TextWrapping="Wrap" Text="{Binding CurrentReader.AltContactMethods, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
    <Button x:Name="btnAddReader" Command="{Binding AddR, UpdateSourceTrigger=PropertyChanged}" Content="Add" HorizontalAlignment="Left" Margin="25,177,0,0" VerticalAlignment="Top" Width="60"/>
    <Button x:Name="btnDeleteReader" Command="{Binding DeleteR, UpdateSourceTrigger=PropertyChanged}" Content="Delete" HorizontalAlignment="Left" Margin="155,177,0,0" VerticalAlignment="Top" Width="60"/>
    <Button x:Name="btnClearReader" Command="{Binding ClearR, UpdateSourceTrigger=PropertyChanged}" Content="Clear" HorizontalAlignment="Left" Margin="220,177,0,0" VerticalAlignment="Top" Width="60"/>
    <Button x:Name="btnEditReader" Command="{Binding EditR, UpdateSourceTrigger=PropertyChanged}" Content="Save" HorizontalAlignment="Left" Margin="90,177,0,0" VerticalAlignment="Top" Width="60"/>

</Grid>

public class HomeViewModel : ViewModelBase
{
    private Reader selectedReader;
    private Book selectedBook;
    private BookListFilter selectedFilter;


    private ObservableCollection<Book> bookList;
    private ObservableCollection<Reader> readerList;
    private IEnumerable<BookListFilter> bookLstItemSrc;

    public HomeViewModel(MainWindowViewModel _mwvm)
    {
        Mwvm = _mwvm;
        SelectedReader = new Reader();
        SelectedBook = new Book();
        SelectedFilter = BookListFilter.AllBooks;

        BookDBDataContext rdb = new BookDBDataContext();

        ReadersList = new ObservableCollection<Reader>(rdb.Readers);
        GetBookList();

        EditReaderSwitch = new DefCommand(EditReaderInfo);
        EditBookSwitch = new DefCommand(EditBookInfo);
    }

    public DefCommand EditReaderSwitch { get; private set; }
    public DefCommand EditBookSwitch { get; private set; }

    public MainWindowViewModel Mwvm { get; set; }

    //Reader List
    public ObservableCollection<Reader> ReadersList
    {
        get { return readerList; }
        set
        {
            if (readerList != value)
            {
                readerList = value;
                RaisePropertyChanged();
            }
        }
    }

public class ReaderManagingViewModel : ViewModelBase
{
    private static Reader currentReader;

    public ReaderManagingViewModel(HomeViewModel hvm)
    {
        if (CurrentReader == null)
            CurrentReader = new Reader();

        CurrentReader = hvm.SelectedReader;

        AddR = new DefCommand(AddReader);
        EditR = new DefCommand(UpdateReader);
        DeleteR = new DefCommand(DeleteReader);
        ClearR = new DefCommand(ClearReaderFields);
    }


    public Reader CurrentReader
    {
        get { return currentReader; }
        set
        {
            if (currentReader != value)
            {
                currentReader = value;
                RaisePropertyChanged();
            }
        }
    }

    public DefCommand AddR { get; private set; }
    public DefCommand EditR { get; private set; }
    public DefCommand DeleteR { get; private set; }
    public DefCommand ClearR { get; private set; }

    private void AddReader()
    {
        BookDBDataContext db = new BookDBDataContext();
        Reader rObj = new Reader();
        rObj.FullName = CurrentReader.FullName;
        rObj.SerialNumber = CurrentReader.SerialNumber;
        rObj.Id = CurrentReader.Id;
        rObj.Adress = CurrentReader.Adress;
        rObj.AltContactMethods = CurrentReader.AltContactMethods;


        try
        {
            db.Readers.InsertOnSubmit(rObj);
            db.Readers.Context.SubmitChanges();
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
        //Console.WriteLine("addingrrrr");
    }

    private void UpdateReader()
    {
        BookDBDataContext db = new BookDBDataContext();
        var qry = from reader in db.Readers
                  where reader.Id == CurrentReader.Id
                  select reader;
        foreach (Reader r in qry)
        {
            r.FullName = CurrentReader.FullName;
            r.SerialNumber = CurrentReader.SerialNumber;
            r.IdNumber = CurrentReader.IdNumber;
            r.Adress = CurrentReader.Adress;
            r.AltContactMethods = CurrentReader.AltContactMethods;
        }

        try
        {
            db.SubmitChanges();
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
        //Console.WriteLine("editinrrrrr");
    }

    private void DeleteReader()
    {
        BookDBDataContext db = new BookDBDataContext();
        var rbTbl = (from r in db.RentedBooks
                 where r.ReaderId == CurrentReader.Id
                 select r);
        var rTbl = (from r in db.Readers
                   where r.Id == CurrentReader.Id
                   select r).SingleOrDefault();
        try
        {
            foreach (var rbr in rbTbl)
            {
                db.RentedBooks.DeleteOnSubmit(rbr);
            }

            db.Readers.DeleteOnSubmit(rTbl);
            db.SubmitChanges();
        }
        catch(Exception e)
        {
            Console.WriteLine(e);
        }
        Console.WriteLine("deleting");
    }}

<UserControl.Resources>

<pre>
<ControlTemplate x:Key="myTemplate" 
                    TargetType="{x:Type ComboBox}">

    <Grid>

        <Popup x:Name="PART_Popup"
                IsOpen="{TemplateBinding IsDropDownOpen}">

            <Button Height="100"
                        Width="100"
                        Content="Hello"/>

        </Popup>

    </Grid>

</ControlTemplate>

<ComboBox Grid.Row="0" 
            Grid.Column="3"
            Background="Red"
            x:Name="comboBox"
            Width="150"
            Template="{Binding StringFormat=myTemplate}">