Добавление текста и значения в ComboBox в WPF

У меня есть следующий код WinForm по этой ссылке: http://net-informations.com/q/faq/combovalue.html

Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim comboSource As New Dictionary(Of String, String)()
    comboSource.Add("1", "Sunday")
    comboSource.Add("2", "Monday")
    comboSource.Add("3", "Tuesday")
    comboSource.Add("4", "Wednesday")
    comboSource.Add("5", "Thursday")
    comboSource.Add("6", "Friday")
    comboSource.Add("7", "Saturday")
    ComboBox1.DataSource = New BindingSource(comboSource, Nothing)
    ComboBox1.DisplayMember = "Value"
    ComboBox1.ValueMember = "Key"
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim key As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Key
    Dim value As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Value
    MessageBox.Show(key & "   " & value)
End Sub
End Class

Я попытался преобразовать приведенные выше коды WinForm в коды WPF, как показано ниже.

xaml

<Window x:Class = "MainWindow"
xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
Title = "MainWindow" Height = "350" Width = "525">
<StackPanel>
    <Button x:Name = "Button1" Height = "25" Width = "100" Content = "Click Me"/>
    <ComboBox x:Name = "ComboBox1" Height = "25" Width = "200"/>
</StackPanel>
</Window>

код позади

Class MainWindow
Private Sub MainWindow_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
    Dim comboSource As New Dictionary(Of String, String)()
    comboSource.Add("1", "Sunday")
    comboSource.Add("2", "Monday")
    comboSource.Add("3", "Tuesday")
    comboSource.Add("4", "Wednesday")
    comboSource.Add("5", "Thursday")
    comboSource.Add("6", "Friday")
    comboSource.Add("7", "Saturday")
    ComboBox1.DataSource = New BindingSource(comboSource, Nothing)
    ComboBox1.DisplayMember = "Value"
    ComboBox1.ValueMember = "Key"
End Sub
Private Sub Button1_Click(sender As Object, e As RoutedEventArgs) Handles Button1.Click
    Dim key As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Key
    Dim value As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Value
    MessageBox.Show(key & "   " & value)
End Sub
End Class

Но я сталкиваюсь с некоторыми ошибками, как вы можете видеть на этом рисунке: https://prnt.sc/na5iie

Итак, как я могу решить эти ошибки?