黑马程序员 省市选择笔记

using (SqlConnection con = new SqlConnection(@"Data Source=.;AttachDBFilename=|DataDirectory|\db1.mdf;Integrated Security=True;User Instence=True"))

{

con.Open();

using (SqlCommand cmd = con.CreateCommand())

{

cmd.CommandText = "select * from T_table";

using (SqlDataReader dr = cmd.ExecuteReader())

{

while (dr.Read())

{

ProvinceItem item = new ProvinceItem();//实例化类，新建对象

item.Id = dr.GetInt32(dr.GetOrdinal("Id"));//将查询到的数据的id值赋给id字段

item.Name = dr.GetString(dr.GetOrdinal("Name"));//同上

cmb省.Items.Add(item);//绑定数据到控件

}

}

}

ProvinceItem item = (ProvinceItem)cmb省.SelectedItem;//创建并转换对象

int Id = item.Id;//将选中的省的Id赋给市中id的字段

using (SqlConnection con = new SqlConnection(@"Data Source=.;AttachDBFilename=|DataDirectory|\db1.mdf;Integrated Security=True;User Instence=True"))

{

con.Open();

using (SqlCommand cmd = con.CreateCommand())

{

cmd.CommandText = "select * from T_table where Id=@Id";   //查询市中id与省中的id值相等的信息

cmd.Parameters.Add(new SqlParameter("Id",Id));

using (SqlDataReader dr = cmd.ExecuteReader())

{

while (dr.Read())

{

string cityItem = dr.GetString(dr.GetOrdinal("cityItem"));

cmb市.Items.Add(cityItem);

}

}

}

}

class ProvinceItem//定义类。从这看出类的重要作用，可以传值。

{

public string Name{set;get;}

public int Id{set;get;}

}