VS在此行發出錯誤: Label1.Text = DropDownList1.SelectedItem.Text;標籤不顯示下拉列表中選擇的值
錯誤消息說對象引用未設置爲對象的實例。什麼可能是解決方案?
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
namespace Login
{
public partial class ViewCourses : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string loginID = Convert.ToString(Session[0]);
DropDownList1.SelectedValue = loginID;
Label1.Text = DropDownList1.SelectedItem.Text;
}
}
}
Label1.Text = DropDownList1.SelectedItem.Text; 最初沒有在下拉列表中選擇(當頁面已被加載時),因此DropDownList1.SelectedItem爲null。 –