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"];            }                   }    }}