ComBox 控件的两级联动

这是主窗体 用MySchool 来做一个例子 第一个combox绑定的是Grade表 第二个是Subject表

运行后的效果如下:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data;

namespace 两级联动
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
//窗体事件
private void Form1_Load(object sender, EventArgs e)
{
string strcon = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
SqlConnection con = new SqlConnection(strcon);
string sql = "select * from grade";
SqlDataAdapter da = new SqlDataAdapter(sql, con);
DataSet ds = new DataSet();
da.Fill(ds,"gradeinfo");
cboGrade.DataSource = ds.Tables["gradeinfo"];
cboGrade.DisplayMember = "gradename";
cboGrade.ValueMember = "gradeid";

}
 

//双击第一个控件的事件
private void cboGrade_SelectedIndexChanged(object sender, EventArgs e)
{

string strcon = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
SqlConnection con = new SqlConnection(strcon);
con.Open();
string gradename = cboGrade.Text;
int gradeid = idbyname(gradename);
string sql = "select * from subject where gradeid =@gradeid";
SqlParameter para = new SqlParameter("@gradeid", gradeid);
SqlCommand com = new SqlCommand(sql, con);
com.Parameters.Add(para);
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = com;
DataSet ds = new DataSet();
da.Fill(ds, "subjectinfo");
cboSubject.DataSource = ds.Tables["subjectinfo"];
cboSubject.DisplayMember = "subjectname";
cboSubject.ValueMember = "subjectid";

}
//通过科目名字获取科目id
public int idbyname(string name)
{
string strcon = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
SqlConnection con = new SqlConnection(strcon);
string sql = "select gradeid from grade where gradename='" + name + "'";
SqlCommand com = new SqlCommand(sql, con);
con.Open();
int gradeid = Convert.ToInt32(com.ExecuteScalar());
if (gradeid>0)
{
return gradeid;
}
return 0;
}

}
}