Question

sql = "select * from gwc where username='" + Session["username1"].ToString()

堆栈跟踪: [NullReferenceException: 未将对象引用设置到对象的实例。] ddlist.Page_Load(Object sender, EventArgs e) in c:\Users\lenovo\Desktop\myNewspaper\ddlist.aspx.cs:18 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35 System.Web.UI.Control.OnLoad(EventArgs e) +99 System.Web.UI.Control.LoadRecursive() +50 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

Answer 1

个人觉得把，你可以先把 Session["username1"].ToString() 赋值给一个string
比如： string username = “”;
if(Session["username1"]!=null)
{
username = Session["username1"].ToString()
}
sq语句