WPF 中保存当前 DataGrid 的数据到数据库中问题
前台： 

       <DataGrid HorizontalAlignment="Left" 
                  Name="dg_datagrid" Height="117" 
                  Margin="209,32,0,0" 
                  VerticalAlignment="Top" Width="232" 
                  AutoGenerateColumns="False">
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding Path=ShipperID}"
                                    Header="编号"/>
                <DataGridTextColumn Binding="{Binding Path=CompanyName}"
                                    Header="名称"/>
                <DataGridTextColumn Binding="{Binding Path=Phone}"
                                    Header="号码"/>
            </DataGrid.Columns>
        </DataGrid>

后台：

        private void save_Click(object sender, RoutedEventArgs e)
        {
            dt = (dg_datagrid.ItemsSource as DataView).Table;
            SqlConnection conn = new SqlConnection(@"Data Source=.\SQLExpress;Initial Catalog=WPF_for_ado;Integrated Security=True");
            SqlCommand cmd = new SqlCommand(sql_load,conn);
            sda = new SqlDataAdapter(cmd);
            SqlCommandBuilder cb = new SqlCommandBuilder(sda);
            cb.RefreshSchema();
            sda.Update(dt);                                             ------------------------------------------------->运行的时候，报错
            MessageBox.Show("完成保存!", "提示", MessageBoxButton.OK);
  &nbs