自学.net（6）DBNULL

using System;

using System.Collections.Generic;

using System.Data;

using System.Data.SqlClient;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Data;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Imaging;

using System.Windows.Navigation;

using System.Windows.Shapes;



namespace DBNULL

{

    /// <summary>

    /// MainWindow.xaml 的交互逻辑

    /// </summary>

    public partial class MainWindow : Window

    {

        public MainWindow()

        {

            InitializeComponent();

        }



        private void btn1_Click(object sender, RoutedEventArgs e)

        {

            object objName;

            object objAge;

            object objHeight;



            string name=tbName.Text;

            string age=tbAge.Text;

            string height=tbHeight.Text;



            if (name.Length<=0)

            {

                objName = DBNull.Value;

            }

            else

            {

                objName = name;

            }



            if (age.Length <= 0)

            {

                objAge = DBNull.Value;

            }

            else

            {

                objAge = name;

            }



            if (height.Length <= 0)

            {

                objHeight = DBNull.Value;

            }

            else

            {

                objHeight = height;

            }



            SqlHelper.ExecuteNonQuery(@"insert into T_Null(Name,Age,Height) 

            values (@Name,@Age,@Height)",

             new SqlParameter("@Name", objName),

             new SqlParameter("@Age", objAge),

             new SqlParameter("@Height", objHeight));

        }



        private void btn2_Click(object sender, RoutedEventArgs e)

        {

            DataTable table= SqlHelper.ExecuteDataTable("select * from T_Null where Id=7");

            DataRow row = table.Rows[0];

            string name;

            if (row["Name"]==DBNull.Value)

            {

                name = null;

            }

            else

            {

                name = (string)row["Name"];

            }



            int? age; //int类型不能转换为null值，int?为可空数据类型

            if (row["Age"]==DBNull.Value)

            {

                age = null;

            }

            else

            {

                age = (int)row["Age"];

            }



             int? height;

            if (row["Height"]==DBNull.Value)

            {

                height = null;

            }

            else

            {

                height = (int)row["Height"];

            }

           

        }

    }

}