c# WPF Adding a combobox item to a listbox

Question

I'm trying to make it so that a user can choose an item from a combo box, press a button and the selected item will be added to a listbox. The problem is that once I make any choice and press the button - the listbox seems to glitch out and the horizontal scrolling slider pops up and takes up the entire space (don't even know if the item gets added).

XAML code:

<Label Name="UserEntryLabel" Content="Your chosen entries:" Grid.Row="1" Grid.ColumnSpan="2"  Grid.Column="0" HorizontalAlignment="Right" VerticalAlignment="Bottom" FontSize="15" FontWeight="Bold" Foreground="DarkBlue" Margin="0,0,10,8" Padding="0,0,0,0"/>
<ListBox Name="UserEntryBox" Grid.Row="1" Grid.Column="2" HorizontalAlignment="Left" VerticalAlignment="Bottom" Width="120" Height="20" ScrollViewer.VerticalScrollBarVisibility="Visible" Margin="0,0,0,8"/>
<Label Name="NewEntryLabel" Content="Add new entry:" Grid.Row="2"  Grid.Column="0" HorizontalAlignment="Right" VerticalAlignment="Top" FontSize="15" FontWeight="Bold" Foreground="DarkBlue" Margin="0,8,6,0" Padding="0,0,0,0"/>
<ComboBox Name="NewEntryBox" Grid.Row="2" Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Top" Width="120" Height="20" Margin="0,8,0,0">
    <ComboBoxItem IsSelected="True">Entry1</ComboBoxItem>
    <ComboBoxItem>Entry2</ComboBoxItem>
    <ComboBoxItem>Entry3</ComboBoxItem>
    <ComboBoxItem>Entry4</ComboBoxItem>
</ComboBox>
<Button Name="NewEntryButton" Content="Add" Grid.Row="2" Grid.Column="2" HorizontalAlignment="left" VerticalAlignment="Top" Width="90" Height="20" Margin="0,8,0,0" Click="NewChestButtonClick"/>

CS code:

private void NewCEntryButtonClick(object sender, RoutedEventArgs e)
{
    AddNewEntry();
}

private void AddNewEntry()
{
    ListBoxItem TempItem = new ListBoxItem();
    string EntryType = NewEntryBox.SelectedItem.ToString();
    TempItem.Content = EntryType;
    UserEntryBox.Items.Add(TempItem);
}

Answer 1

Your problem is that you weren't adding the value in the combobox but the whole item reference too :

System.Windows.Controls.ComboBoxItem: Entry1

If you change how you add the value of the combobox you can see it appear in the listbox :

private void AddNewEntry()
{
    UserEntryBox.Items.Add(NewEntryBox.Text);
}