Tạo checkBox nằm trong ListBox lỗi: A first chance exception of type 'System.ArgumentNullException' occurred

[churanluoi]

<Window x:Class="WPF_CheckListBox.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" Loaded="Window_Loaded">
    
    <Window.Resources>
        
        <DataTemplate x:Key="CheckListBox">
            <StackPanel Orientation="Horizontal">

                <CheckBox Name="ChkList" Content="{Binding Path=ProdName}"></CheckBox>
               
            </StackPanel>
        </DataTemplate>
    </Window.Resources>  
    
    <Grid>
        <ListBox Height="181" HorizontalAlignment="Left" Margin="179,12,0,0" Name="listBox1" VerticalAlignment="Top" Width="159" ItemTemplate="{StaticResource CheckListBox}" ItemsSource="{Binding}" />
        <Button x:Name="btnOk" Height="23" Width="80" Margin="219,210,204,78" Content="OK" Click="btnOk_Click"></Button>
    </Grid>
</Window>

namespace WPF_CheckListBox
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                listBox1.DataContext = GetTableName(); // Bind Tables Name in ListBox
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
        }

        private void btnOk_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                GetSelectedCheckObjItem(); // Get a selected checkbox items
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);   
            }
        }

        #region Methods
        /// <summary>
        /// Get table name from nortwind databases
        /// </summary>
        /// <returns>DataTable</returns>
        private DataTable GetTableName()
        {
            try
            {
                SqlConnection SqlCon = new SqlConnection();
                SqlCon.ConnectionString = @"Data Source=DANH-PC;Initial Catalog=shradhabookstores;Persist Security Info=True;User ID=sa;Password=123456";
                SqlCon.Open();

                SqlCommand SqlComm = new SqlCommand("SELECT [ProdName] FROM Products");
                SqlComm.Connection = SqlCon;

                DataTable Table = new DataTable();
                SqlDataAdapter SqlDa = new SqlDataAdapter();
                SqlDa.SelectCommand = SqlComm;
                SqlDa.Fill(Table);

                return Table; 
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);  
            }
        }

        /// <summary>
        /// Find Child Control from ContentPresenter
        /// </summary>
        /// <typeparam name="ChildControl"></typeparam>
        /// <param name="DependencyObj"></param>
        /// <returns></returns>
        private ChildControl FindVisualChild<ChildControl>(DependencyObject DependencyObj)
        where ChildControl : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(DependencyObj); i++)
            {
                DependencyObject Child = VisualTreeHelper.GetChild(DependencyObj, i);

                if (Child != null && Child is ChildControl)
                {
                    return (ChildControl)Child;
                }
                else
                {
                    ChildControl ChildOfChild = FindVisualChild<ChildControl>(Child);

                    if (ChildOfChild != null)
                    {
                        return ChildOfChild;
                    }
                }
            }
            return null;
        }

        /// <summary>
        /// Get a selected checkbox items
        /// </summary>
        private void GetSelectedCheckObjItem()
        {
            StringBuilder sb = new StringBuilder();
            try
            {
                for (int i = 0; i < listBox1.Items.Count; i++)
                {
                    // Get a all list items from listbox
                    ListBoxItem ListBoxItemObj = (ListBoxItem)listBox1.ItemContainerGenerator.ContainerFromItem(listBox1.Items[i]);

                    // find a ContentPresenter of that list item.. [Call FindVisualChild Method]
                    ContentPresenter ContentPresenterObj = FindVisualChild<ContentPresenter>(ListBoxItemObj);

                    // call FindName on the DataTemplate of that ContentPresenter
                    DataTemplate DataTemplateObj = ContentPresenterObj.ContentTemplate;
                    CheckBox Chk = (CheckBox)DataTemplateObj.FindName("ChkList", ContentPresenterObj);

                    // get a selected checkbox items.
                    if (Chk.IsChecked == true)
                    {
                       // MessageBox.Show(Chk.Content.ToString().Trim()); 
                        sb.Append(Chk.Content.ToString() + ",");
                    }
                }
                Console.WriteLine(sb);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);  
            }
        }

        #endregion
    }
}

khi chay nếu listbox có thanh trượt (nhiều dòng) thì sẽ xảy ra lỗi
A first chance exception of type 'System.ArgumentNullException' occurred in PresentationCore.dll
A first chance exception of type 'System.Exception' occurred in WPF_CheckListBox.exe

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