Items collection must be empty before using ItemsSource. : <p>I Have "Items collection must be empty before using ItemsSource." Error In My Code</p>

<p>I Test All Answer in StackOverFlow Links But They Did not Work!
My Xaml :</p>

<pre><code>&lt;Window x:Class="FirstWpfTestApplication.Main"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:FirstWpfTestApplication"
    xmlns:valConverter="clr-namespace:FirstWpfTestApplication.Model.ValueConverters"
    mc:Ignorable="d"
    Title="Main" Height="500" Width="800" WindowStartupLocation="CenterScreen"&gt;
&lt;UserControl&gt;
    &lt;UserControl.Resources&gt;
        &lt;valConverter:GenderConverter x:Key="GenderConverter"/&gt;
        &lt;valConverter:EnumList x:Key="EnumConverter"/&gt;
        &lt;Style TargetType="TextBox"&gt;
            &lt;Setter Property="MinWidth" Value="100"/&gt;
            &lt;Setter Property="Margin" Value="5"/&gt;
        &lt;/Style&gt;
        &lt;Style TargetType="TextBlock"&gt;
            &lt;Setter Property="Margin" Value="5"/&gt;
        &lt;/Style&gt;
        &lt;Style TargetType="RadioButton"&gt;
            &lt;Setter Property="Margin" Value="5"/&gt;
        &lt;/Style&gt;
        &lt;Style TargetType="CheckBox"&gt;
            &lt;Setter Property="Margin" Value="5"/&gt;
        &lt;/Style&gt;
        &lt;Style TargetType="ComboBox"&gt;
            &lt;Setter Property="MinWidth" Value="100"/&gt;
        &lt;/Style&gt;
        &lt;Style TargetType="Button"&gt;
            &lt;Setter Property="Margin" Value="5"/&gt;
            &lt;Setter Property="MinWidth" Value="60"/&gt;
        &lt;/Style&gt;
    &lt;/UserControl.Resources&gt;
    &lt;Grid&gt;
        &lt;DockPanel&gt;
            &lt;!--&lt;ListBox Name="lstPeople" DockPanel.Dock="Left"&gt;
                &lt;DataTemplate&gt;
                    &lt;StackPanel Orientation="Horizontal"&gt;
                        &lt;TextBlock Text="Name:" Margin="10 0"/&gt;
                        &lt;TextBlock Text="{Binding Name}" Margin="10 0"/&gt;
                    &lt;/StackPanel&gt;
                &lt;/DataTemplate&gt;
            &lt;/ListBox&gt;--&gt;
            &lt;Border BorderThickness="2" BorderBrush="Black" CornerRadius="1"&gt;
                &lt;Grid&gt;
                    &lt;Grid.ColumnDefinitions&gt;
                        &lt;ColumnDefinition Width="auto"/&gt;
                    &lt;/Grid.ColumnDefinitions&gt;
                    &lt;Grid.RowDefinitions&gt;
                        &lt;RowDefinition Height="auto"/&gt;
                        &lt;RowDefinition Height="auto"/&gt;
                        &lt;RowDefinition Height="auto"/&gt;
                        &lt;RowDefinition Height="auto"/&gt;
                        &lt;RowDefinition Height="auto"/&gt;
                    &lt;/Grid.RowDefinitions&gt;
                    &lt;StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="0" Margin="10"&gt;
                        &lt;TextBlock&gt;Name:&lt;/TextBlock&gt;
                        &lt;TextBox Text="{Binding Name}"&gt;&lt;/TextBox&gt;
                    &lt;/StackPanel&gt;
                    &lt;StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="1" Margin="10"&gt;
                        &lt;TextBlock VerticalAlignment="Center"&gt;Gender:&lt;/TextBlock&gt;
                        &lt;WrapPanel Orientation="Vertical"&gt;
                            &lt;RadioButton IsChecked="{Binding Gender,Converter={StaticResource GenderConverter},ConverterParameter=True}"
                            Name="rdMan"&gt;
                                Man
                            &lt;/RadioButton&gt;
                            &lt;RadioButton IsChecked="{Binding Gender,Converter={StaticResource GenderConverter},ConverterParameter=False}"
                             Name="rdWoman"&gt;
                                WoMan
                            &lt;/RadioButton&gt;
                        &lt;/WrapPanel&gt;
                    &lt;/StackPanel&gt;
                    &lt;StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="2" Margin="10"&gt;
                        &lt;TextBlock&gt;Field Of Work:&lt;/TextBlock&gt;
                        &lt;StackPanel Orientation="Horizontal"&gt;
                            &lt;CheckBox Name="chActor" IsChecked="{Binding FieldOfWorks,Converter={StaticResource EnumConverter},ConverterParameter=Actor}"&gt;
                                Actor
                            &lt;/CheckBox&gt;
                            &lt;CheckBox Name="chDirector" IsChecked="{Binding FieldOfWorks,Converter={StaticResource EnumConverter},ConverterParameter=Director}"&gt;
                                Director
                            &lt;/CheckBox&gt;
                            &lt;CheckBox Name="chProducer" IsChecked="{Binding FieldOfWorks,Converter={StaticResource EnumConverter},ConverterParameter=Producer}"&gt;
                                Producer
                            &lt;/CheckBox&gt;
                        &lt;/StackPanel&gt;
                    &lt;/StackPanel&gt;
                    &lt;StackPanel Grid.Row="3" Orientation="Horizontal"&gt;
                        &lt;TextBlock&gt;Country:&lt;/TextBlock&gt;
                        &lt;ComboBox Name="cbCountries"&gt;
                            &lt;DataTemplate&gt;
                                &lt;TextBlock Text="{Binding Name}"/&gt;
                            &lt;/DataTemplate&gt;
                        &lt;/ComboBox&gt;
                    &lt;/StackPanel&gt;
                    &lt;StackPanel Margin="0 10" HorizontalAlignment="Left" Orientation="Horizontal" Grid.Row="4"&gt;
                        &lt;Button&gt;Save&lt;/Button&gt;
                    &lt;/StackPanel&gt;
                &lt;/Grid&gt;
            &lt;/Border&gt;
        &lt;/DockPanel&gt;
    &lt;/Grid&gt;
&lt;/UserControl&gt;
</code></pre>

<p></p>

<p>And My C# Code:</p>

<pre><code>    public partial class Main : Window
{
    public List&lt;People&gt; PeopleContext;        
    public Main()
    {
        InitializeComponent();

        this.DataContext = People.GetPeople();
        cbCountries.ItemsSource = new Country().GetCountries();//In This Line Exception Will Throw


    }
}
</code></pre>

<p>Please Help To Fix This Problem In WPF</p>
