项目需求：根据年级下拉框的变化使得科目下拉框绑定次年级下对应有的值
我们用三层架构的模式来实现
1.我们想和数据库交互，我们首先得来先解决dal数据库交互层
01.获得年级下拉框的数据
在gradedal类中
using system;
using system.collections.generic;
using system.linq;
using system.text;
using system.threading.tasks;
using system.data.sqlclient;
using system.data;
using myschool.model;
using system.configuration;
namespace myschool.dal
{
//数据访问层
public class gradedal
{
public static string constr = configurationmanager.connectionstrings[ "constr" ].connectionstring;
#region 获得年级表
public datatable selectgrade( string gradetype)
{
//和数据库交互
string str = "data source=.;initial catalog=myschool;uid=sa" ;
sqlconnection con = new sqlconnection(str);
string sql = "" ;
if (gradetype== "" )
{
sql = "select * from grade" ;
}
else
{
sql = "select * from student where gradeid in (select gradeid from grade where gradename='" + gradetype + "')" ;
}
sqldataadapter da = new sqldataadapter(sql, con);
dataset ds = new dataset();
//捕获异常
try
{
da.fill(ds, "stuinfo" );
}
catch (exception ex)
{
throw new exception(ex.message);
}
//返回一张表的数据
return ds.tables[ "stuinfo" ];
}
#endregion
#region 获取年级数据，为在下拉框中显示
//定义一个集合,储存年级信息
list<grade> list = new list<grade>();
#region 方法一: 以返回表的方式
public datatable loadcombox()
{
string sql = "select * from grade" ;
datatable dt = sqlhelper.executedatatable(sql);
return dt;
}
#endregion
#region 方法二:以返回集合的方式
public list<grade> loadcombox2()
{
string sql = "select * from grade" ;
datatable dt = sqlhelper.executedatatable(sql);
//方法一：
foreach (datarow row in dt.rows)
{
//每一个row代表表中的一行,所以一行对应一个年级对象
grade grade = new grade();
grade.gradeid = convert.toint32(row[ "gradeid" ]);
grade.gradename = row[ "gradename" ].tostring();
list.add(grade);
}
//方法二：(使用mytool类)
//mytool tool=new mytool();
//list = tool.datatabletolist<grade>(dt);
return list;
}
#endregion
#region 方法三：要求使用using语句
public list<grade> loadcombox3()
{
//using的作用可以释放资源，利于资源的回收（可以省略关闭连接）
using (sqlconnection con= new sqlconnection(constr))
{
try
{
string sql = "select * from grade" ;
sqlcommand cmd = new sqlcommand(sql,con);
con.open();
sqldatareader dr = cmd.executereader();
while (dr.read())
{
grade gr = new grade();
gr.gradeid = convert.toint32(dr[ "gradeid" ]);
gr.gradename=dr[ "gradename" ].tostring();
list.add(gr);
}
}
catch (exception ex)
{
throw new exception(ex.message);
}
}
return list;
}
#endregion
#endregion
}
}
02.在业务逻辑层
using system;
using system.collections.generic;
using system.linq;
using system.text;
using system.threading.tasks;
using myschool.dal;
using system.data;
using myschool.model;
namespace myschool.bll
{
public class gradebll
{
gradedal gradedal = new gradedal();
#region 获取年级数据，为在下拉框中显示
public datatable selectgrade( string gradetype)
{
return gradedal.selectgrade(gradetype);
}
public datatable loadcombox()
{
return gradedal.loadcombox();
}
public list<grade> loadcombox2()
{
return gradedal.loadcombox2();
}
#endregion
public list<grade> loadcombox3()
{
return gradedal.loadcombox3();
}
}
}
03.在窗体ui层
在load事件中加载年级下拉框
private void frmselectresult_load( object sender, eventargs e)
{
#region 加载年级下拉框
try
{
list<grade> list = gradedal.loadcombox3();
list.insert(0, new grade() { gradeid=-1,gradename= "--全部--" });
cbograde.valuemember = "gradeid" ;
cbograde.displaymember = "gradename" ;
cbograde.datasource = list;
}
catch (exception ex)
{
messagebox.show(ex.message);
}
#endregion
#region 加载科目下拉框
//try
//{
// list2 = subjectdal.loadcomboxsub();
// list2.insert(0, new subject() { subjectid = -1, subjectname = "--全部--" });
// cbosubject.valuemember = "subjectid";
// cbosubject.displaymember = "subjectname";
// cbosubject.datasource = list2;
//}
//catch (exception ex)
//{
// messagebox.show(ex.message);
//}
#endregion
}
其中在使用
获得年级下拉框隐藏值得方法（2）
int num = convert.toint32(cbograde.selectedvalue);
加载年级下拉框时：会出现的错误的写法
把cbograde.datasource = list;写在
cbograde.valuemember = "gradeid";
cbograde.displaymember = "gradename"; 上面
即：
#region 加载年级下拉框
try
{
list<grade> list = gradedal.loadcombox3();
list.insert(0, new grade() { gradeid=-1,gradename= "--全部--" });
cbograde.datasource = list;
cbograde.valuemember = "gradeid" ;
cbograde.displaymember = "gradename" ;
}
catch (exception ex)
{
messagebox.show(ex.message);
}
#endregion
这是就会出现下面错误：
在年级的selectedindexchanged事件中
try
{
//根据年级取得科目信息并绑定
#region 获得年级下拉框隐藏值得方法（1）
grade sub = (grade)cbograde.selecteditem;
int num =sub.gradeid;
#endregion
#region 获得年级下拉框隐藏值得方法（2）
// int num = convert.toint32(cbograde.selectedvalue.tostring());
#endregion
list<subject> list = subjectdal.loadcomboxsub2(num);
cbosubject.valuemember = "subjectid" ;
cbosubject.displaymember = "subjectname" ;
cbosubject.datasource = list;
}
catch (exception)
{
messagebox.show( "出错" );
}
以上就是本文的全部内容，希望对大家学习c#程序设计有所帮助。
dy("nrwz");
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