如何在页面加载时填充下拉列表 [英] how to fill dropdownlist on page load

问题描述

大家好，
我收到以下错误，以使以下代码填充下拉列表"ddlstuid":

错误ocurredSystem.NullReferenceException:对象引用未设置为对象的实例.在IAP.Attendance.Page_Load(对象发送者，EventArgs e)处.

请告诉我如何清除上述错误.

代码:

Hello All,
I am getting this error for the following code to fill the dropdownlist ''ddlstuid'' :

Error ocurredSystem.NullReferenceException: Object reference not set to an instance of an object. at IAP.Attendance.Page_Load(Object sender, EventArgs e).

pls tell me how to remove the above error.

code:

SqlConnection myconn;
SqlCommand cmd;
string str = "Data Source=TIMSCDR\\SQLEXPRESS;Initial Catalog=IAP;Integrated Security=True";
SqlDataReader dr;

protected void Page_Load(object sender, EventArgs e)
{
    try
    {
        cmd = new SqlCommand("select stuid from attendance", myconn);
        myconn.Open();
        ddlstuid.Items.Clear();
        dr = cmd.ExecuteReader();
        if (dr != null)
        {
            while (dr.Read())
            {
                ddlstuid.Items.Add(dr["stuid"].ToString());
            }
        }
        myconn.Close();
    }
    catch (Exception e1)
    {
        Label45.Text = "Error ocurred" + e1;
    }

在此先感谢.

Thanks in Advance.

推荐答案

public void bind()
{
sqldataadapter da =新sqldataadapter(从tname中选择*"，cn);
datatable dt = new datatable();
da.fill(dt);
ddlstuid.datasource = dt;
ddlstuid.datatextfield ="colnale";
ddlstuid.datavaluefield ="colname";
ddlstuid.databind();
}

在页面加载中
{
if(！ispostback)
{
bind();
}
}

public void bind()
{
sqldataadapter da=new sqldataadapter("select * from tname",cn);
datatable dt=new datatable();
da.fill(dt);
ddlstuid.datasource=dt;
ddlstuid.datatextfield="colnale";
ddlstuid.datavaluefield="colname";
ddlstuid.databind();
}

in page load
{
if(!ispostback)
{
bind();
}
}

您似乎没有为"myconn"分配任何内容.尝试添加

You don''t appear to assign anything to "myconn". Try adding

cmd = new SqlCommand("select stuid from attendance", myconn);
myconn = new SqlConnection(str); // --- Add this line
myconn.Open();

别忘了将其放在finally 块中.

^ ]

引用此链接

http://www.java2s.com/Tutorial/ASP.NET/0360__ADO.net-Database/ReaddatafromSQLserverandfillaspdropdownlistC.htm[^]

Refer this link

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