帮我看看这个dropdownlist错在哪里?

[hottm]

protected System.Web.UI.WebControls.TextBox txtId;
protected System.Web.UI.WebControls.TextBox txtName;
protected System.Web.UI.WebControls.DropDownList Dlist;
protected System.Web.UI.WebControls.Button btnOK;
private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
DroplistDataBind();
}
}
private void DroplistDataBind()
{
//省略....
}
private void btnOK_Click(object sender, System.EventArgs e)
{
string Idno = "";
string Iname = "";
string Ixm = "";

Iname = txtName.Text.Trim();

Idno = txtId.Text.Trim();

lxm=Dlist.SelectedValue.Trim();

Response.Redirect("abcde.aspx?Cxm="+Ixm+"&Cno="+Idno+"&Cname="+Iname);
}

private void DropDownList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
}

运行时Dlist绑定正常, 当上面这个button点击后Idno和Iname读取都正常.但lxm老是空的,取不到Dlist中选定的值,怎么回事?

[hottm]

to abandonship(eagles of wind)

不是很明白,能不能具体点.

[xupc]

你把这个
private void DroplistDataBind()
{
//省略....
}
拿出来看看

[theodiact]

因为页面刷新过程中将会重新添加控件，也就是说你的选项就丢了,所以取不出来
不信你可以将默认选择设为第一个，你取的时候一定总是第一个

[hottm]

private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
DroplistDataBind();
}
}
private void DroplistDataBind()
{
SqlCommand CMD = new SqlCommand();
CMD.CommandText = "select distinct xm from xusers order by xm";
abc.DataControl.BindDropWithSQLCommand(CMD,ref Dlist);
Dlist.SelectedValue="hhhhh";
}

[hottm]

abc.DataControl.BindDropWithSQLCommand的代码:

public static void BindDropWithSQLCommand(SqlCommand CMD,ref DropDownList Dlist)
{
SqlConnection Con = new SqlConnection(System.Configuration.ConfigurationSettings.AppSettings.Get("Con11"));
CMD.Connection = Con;
try
{
if (Con.State.ToString() == "Closed")
{
Con.Open();
}
SqlDataReader cReader = CMD.ExecuteReader();
Dlist.DataSource = cReader;
Dlist.DataTextField ="xm";
Dlist.DataBind();
}
catch(SqlException sqlex)
{
HttpContext.Current.Response.Write(sqlex.Message);
}
finally
{
Con.Close();
Con.Dispose();
CMD.Dispose();
}
}

麻烦各位看看,先谢了!

[dayasky]

你只设了Dlist.DataTextField ，没有设置DataValueField

而你却用lxm=Dlist.SelectedValue.Trim();去取值，当然什么也取不到了

解决：
要么给DataValueField赋值
要么取selecteditem 的text值

[冷月孤峰]

dropdownlist的DataValueField没有绑定！当然取不到SelectedValue值啦。你只是绑定了Dlist.DataTextField ="xm";

[hottm]

我在BindDropWithSQLCommand改
Dlist.DataSource = cReader;
Dlist.DataTextField ="xm";
Dlist.DataValueField ="xm";
Dlist.DataBind();

还是不行!

我又改btnOK_Click
lxm=Dlist.SelectedItem.Text;
也不行!

还要麻烦指教一下,谢谢!

[dayasky]

奇怪了
你调试一下看看
到你要取lxm的值的时候，看看那个Dlist，一共有几个item，当前item的text和value和index是什么
应该可以找到原因

[伴老思源]

private void DroplistDataBind()
{
SqlCommand CMD = new SqlCommand();
CMD.CommandText = "select distinct xm from xusers order by xm";
abc.DataControl.BindDropWithSQLCommand(CMD,ref Dlist);
Dlist.SelectedValue="hhhhh";
}
不对，要把值和ID都绑上，
在取值时要
Request.Form就行了

[hy98521]

if(!Page.IsPostBack)

[hottm]

搜了一下之前的帖子,有人碰到过类似的情况,好象之前的办法是重建页面,偶试了还是不行,郁闷...

[daichenghua]

可能是因为你的Dlist的绑定的cReader 没有hhhhh这个植,在你的private void DroplistDataBind()
{
.....
}
又让Dlist的SelectedValue="hhhhh";,这时候Dlist的item为空

[hottm]

不对的,"hhhhh"有的.
哪位大哥帮帮忙给个类似详细的代码例子,偶自己看看错在哪!
谢谢!

[dayasky]

你试试这样：
//在这里取数据
DataTable datatable1 = ....;
if( datatable1.Rows.Count == 0 )
return;

DropDownList1.Items.Clear();
DropDownList1.DataSource = datatable1;
DropDownList1.DataTextField = "city_name";
DropDownList1.DataValueField = "igen_city_code";
DropDownList1.DataBind();

[hottm]

还是不行,不过问题大概找到了,只是不知道如何解决:
偶这样进行测试:
protected System.Web.UI.WebControls.TextBox txtId;
protected System.Web.UI.WebControls.TextBox txtName;
protected System.Web.UI.WebControls.DropDownList DropDown1;
protected System.Web.UI.WebControls.Button btnOK;
private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
DropDown1.Items.Add( new ListItem("厦门"));
DropDown1.Items.Add( new ListItem("深圳"));
DropDown1.Items.Add( new ListItem("珠海"));
DropDown1.Items.Add( new ListItem("大连"));
}
}
private void btnOK_Click(object sender, System.EventArgs e)
{
string Iname = txtName.Text.Trim();
string Idno = txtId.Text.Trim();
string lxm=Dlist.SelectedItem.Text.Trim();
Response.Redirect("abcde.aspx?Cxm="+Ixm+"&Cno="+Idno+"&Cname="+Iname);
}
private void DropDownList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
}
发现点击button后dropdownlist列表的东西都清空了,根本没有进行Redirect跳转.
我把一模一样的程序放在同一计算机的另一sln里(比如Duwnmish)运行就正常了.
不知道.NET framework有什么奥妙在这里?

[hottm]

说明一下:上贴dropdownlist名称是偶发贴是临时改的,所以有出入.
CSDN发完贴不能改顶讨厌的!...

[hottm]

偶改代码如下:
protected System.Web.UI.WebControls.TextBox txtId;
protected System.Web.UI.WebControls.TextBox txtName;
protected System.Web.UI.WebControls.DropDownList Dlist;
protected System.Web.UI.WebControls.Button btnOK;
private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
DroplistDataBind();
}
}
private void DroplistDataBind()
{
SqlCommand CMD = new SqlCommand();
CMD.CommandText = "select distinct xm from xusers order by xm";
abc.DataControl.BindDropWithSQLCommand(CMD,ref Dlist);
Dlist.SelectedValue="hhhhh";
}
private void btnOK_Click(object sender, System.EventArgs e)
{
string Idno = "";
string Iname = "";
string Ixm = "";

Iname = txtName.Text.Trim();

Idno = txtId.Text.Trim();

lxm=Dlist.SelectedItem.Text.Trim();

Response.Redirect("abcde.aspx?Cxm="+Ixm+"&Cno="+Idno+"&Cname="+Iname);
}

private void DropDownList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
}

错误变成:
未将对象引用设置到对象的实例。
指这一行:string lxnxq=DList.SelectedItem.Text.Trim();
该如何处理?
偶下了十几个.NET源码,包括MS的DUWAMISH、PETSHOP，奇怪的是都没有关于DROPDOWNLIST类似的代码。

[hottm]

问题已经找到是viewstates问题.结贴!