Ado.Net小练习03（省市联动）

前台界面：

后台代码：

namespace _04省市联动

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

private int r = 0;

private void Form1_Load(object sender, EventArgs e)

{

r = 1;

//所有省份显示到第一个下拉框中

LoadAreaByAreaPId(0);

}

private void LoadAreaByAreaPId(int v)

{

List<Area> list=new List<Area>();

list.Add(new Area() {AreaId = -1,AreaName = "---请选择---"});

string sql = "select AreaId,AreaName from TblArea where AreaPId="+v;

using (SqlDataReader reader=SqlHelper.ExecuteDataReader(sql))

{

if (reader.HasRows)

{

while (reader.Read())

{

Area a=new Area();

a.AreaId = Convert.ToInt32(reader["AreaId"]);

a.AreaName = reader["AreaName"].ToString();

list.Add(a);

}

}

}

if (r==1)

{

cbPro.DataSource = list;

cbPro.DisplayMember = "AreaName";

cbPro.ValueMember = "AreaId";

}

if(r==2)

{

cbCity.DataSource = list;

cbCity.DisplayMember = "AreaName";

}

}

private void cbPro_SelectedIndexChanged(object sender, EventArgs e)

{

#region 练习用的代码

//if (cbPro.SelectedIndex != 0)

//{

// cbCity.Items.Clear();

// //获取当前省份的id

// int id = Convert.ToInt32(cbPro.SelectedValue);

// string sql = "select AreaId,AreaName from TblArea where AreaPId=" + id;

// //List<Area> list = new List<Area>();

// using (SqlDataReader reader = SqlHelper.ExecuteDataReader(sql))

// {

// if (reader.HasRows)

// {

// while (reader.Read())

// {

// Area a = new Area();

// a.AreaId = Convert.ToInt32(reader["AreaId"]);

// a.AreaName = reader["AreaName"].ToString();

// cbCity.Items.Add(a); //重写了Area类的ToString()方法 public override string ToString()

//否则添加的是类的命名空间 {

return this.AreaName;

}

// }

// }

// }

//}

#endregion

#region 简化写法，使用r变量判断事件

r = 2;

if (cbPro.SelectedIndex != 0)

{

int id = Convert.ToInt32(cbPro.SelectedValue);

LoadAreaByAreaPId(id);

}

#endregion

}

}

}