Question

ASP.NET 未将对象引用设置到对象的实例.

因为前面没有定义session，所以后面没法取值，我应该怎么修改？
if (Session["userid"].ToString() == null)
{
LinkButton1.Text = "登录";
}
else
{
string uid = Session["userid"].ToString();

OleDbConnection mycon = new OleDbConnection();
mycon.ConnectionString = "provider=microsoft.jet.oledb.4.0;data source=" + Server.MapPath("data/agmn.mdb");
mycon.Open();

OleDbCommand com = new OleDbCommand();
com.Connection = mycon;
com.CommandText = "select * from [user] where userid=" + uid;
OleDbDataReader mydr = com.ExecuteReader();

if (mydr.HasRows)
{
mydr.Read();
LinkButton1.Text = mydr["nickname"].ToString();
}
mycon.Close();
}

Answer 1

if (Session["userid"] == null)
{
LinkButton1.Text = "登录";
}
else
{
string uid = Session["userid"].ToString();
.....

吧第一行改了就行了