问题描述
当我从kategorije选择上午项目，新项目被装载到SUB_kategorije，但是当我选择SUB_kategorije项目，当我点击链接它表明我这个错误：
When I choose am item from "kategorije", new items are loaded into "SUB_kategorije", but when I choose the item from SUB_kategorije and when i click on button it shows me this error:
对象引用未设置到对象的实例。
Object reference not set to an instance of an object.
Line 101: kom.Parameters.Add("@podkategorija", SqlDbType.Text).Value =
SUB_kategorije.SelectedItem.ToString();
这是我的源...
推荐答案
问题是你的的Page_Load 。将其更改为：
The problem is your Page_Load. Change it to:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
SqlDataSource df = new SqlDataSource();
df.ConnectionString = conn;
df.SelectCommand = "SELECT [ID], [Kategorije] FROM [kategorije] ";
kategorije.DataSource = df;
kategorije.DataTextField = "Kategorije";
kategorije.DataValueField = "ID";
kategorije.DataBind();
}
}
问题是你重新绑定 kategorije 每次你的code做了回发时间，所以在时间的button1_Click 运行时， kategorije 已重新绑定和重置，让的SelectedValue 为null。
The problem is your rebinding kategorije every time your code does a postback so by the time Button1_Click runs, kategorije has been rebinding and reset so the SelectedValue is null.
当回传发生在的Page_Load code第一次运行，那么的button1_Click 之后运行。移动该code到！的IsPostBack 检查将导致它只能运行在第一时间你的页面加载，而不是之后再次让的SelectedValue 将可用。
When a postback happens your Page_Load code runs first, then the Button1_Click runs right after. Moving that code into a !IsPostBack check will cause it to only run the first time your page loads and not again after so the SelectedValue will be available.
这篇关于列表框中选择asp.net问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！