WPF checkbox binding don't work

my xaml

<GridViewColumn.CellTemplate>
    <DataTemplate>
   <CheckBox DataContext="{Binding check_key}"  
   IsChecked="{Binding IsSelected}" Checked="black_list_item_fn"></CheckBox>
      </DataTemplate>

    </GridViewColumn.CellTemplate>

and c# code

    public class contact_user_data
    {

        public string user_name { get; set; }
        public string user_key { get; set; }
        public string check_key { get; set; }
        public string head_url { get; set; }
        private bool isSelected;
        private string name;

        public bool IsSelected { get; set; }
    }

//update itemssource code

         var source = global_var.black_list_soruce[md5];
        if (source != black_listview.ItemsSource)
        {

        }
        black_listview.ItemsSource = null;
        //  black_listview.Items.Clear();
        black_listview.ItemsSource = source;

        black_list_seting.IsOpen = true;

No matter how I set check box has been unchecked ....

please help me !! I spent three days researching this problem