根据省份选择城市的功能（连接数据库的）

根据http://blog.csdn.net/huangzhe10/archive/2010/08/18/5819802.aspx建立两个表，分别为省份表tb_province，城市表tb_city。



如上图所示布局，左侧ComboBox显示省份列表，右侧ComboBox显示城市列表

双击form的空白处首先把省份的列表加载到ComboBox里来

方法一：

using (SqlConnection conn = new SqlConnection(@"Data Source=./SQLEXPRESS;AttachDBFilename=|DataDirectory|/country.mdf;Integrated Security=True;User Instance=True"))
{
conn.Open();
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "select * from tb_province";
using (SqlDataReader reader = cmd.ExecuteReader())
{
cmbprovince.Items.Clear();
while (reader.Read())
{
string db_provincename = reader.GetString(reader.GetOrdinal("name"));
cmbprovince.Items.Add(db_provincename);
cmbprovince.SelectedIndex = 0;//默认显示第一个省份
}
}
}

方法二：

先增加应用程序配置文件，其代码如下：

<configuration>
<connectionStrings>
<add name="connStr" connectionString="Data Source=./SQLEXPRESS;AttachDBFilename=|DataDirectory|country.mdf;Integrated Security=True;User Instance=True"/>
</connectionStrings>
</configuration>

程序自启动加载省份列表代码：

string connStr = ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
using (SqlConnection conn = new SqlConnection(connStr))
{
conn.Open();
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "select * from tb_province";
using(SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
tb_province item = new tb_province();
item.id = reader.GetInt32(reader.GetOrdinal("id"));
item.name = reader.GetString(reader.GetOrdinal("name"));
cmbprovince.Items.Add(item);
cmbprovince.SelectedIndex = 0;//默认第一个省份
}
}
}

双击省份的ComboBox写其当值改变时的代码：

方法一：

string pname = (string)cmbprovince.SelectedItem;//获取选择的省份名称
using (SqlConnection conn = new SqlConnection(@"Data Source=./SQLEXPRESS;AttachDBFilename=|DataDirectory|/country.mdf;Integrated Security=True;User Instance=True"))
{
conn.Open();
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "select id from tb_province where name=@ne";//根据省份名称选择此省份的id
cmd.Parameters.AddWithValue("ne", pname);
int pid = Convert.ToInt32(cmd.ExecuteScalar());
cmd.Dispose();
SqlCommand citycmd = conn.CreateCommand();
citycmd.CommandText = "select name from tb_city where provinceid=@provinceid";//根据省份的id=城市表中的provinceid，过滤出此省份下的所有城市名
citycmd.Parameters.AddWithValue("provinceid",pid);
using (SqlDataReader reader = citycmd.ExecuteReader())
{
cmbcity.Items.Clear();
while (reader.Read())
{
string cname = reader.GetString(reader.GetOrdinal("name"));
cmbcity.Items.Add(cname);
}
cmbcity.SelectedIndex = 0;//默认显示第一个城市
}
}

方法二：

string connStr = ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
tb_province item=(tb_province)cmbprovince.SelectedItem;
using (SqlConnection conn = new SqlConnection(connStr))
{
conn.Open();
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "select * from tb_city where provinceid=@pid";
cmd.Parameters.Add(new SqlParameter("pid",item.id));
using (SqlDataReader reader = cmd.ExecuteReader())
{
cmbcity.Items.Clear();
while (reader.Read())
{
string city_name = reader.GetString(reader.GetOrdinal("name"));
cmbcity.Items.Add(city_name);
cmbcity.SelectedIndex = 0;//默认选定省份的第一个城市
}
}
}