Int会话变量增加？

Question

Can a session variable be an int ? I want to increment Session["PagesViewed"]+1; every time a page is loaded. I'm getting errors when trying to increment the session variable.

if (Session["PagesViewed"].ToString() == "2")
{
     Session["PagesViewed"] = 0;
}
else
{
     Session["PagesViewed"]++;
}

Answer 1

You need to test to see if the Session variable exists before you can use it and assign to it.

You can do increment as follows.

Session["PagesViewed"] = ((int) Session["PagesViewed"]) + 1;

But, if the Session["PagesViewed"] does not exist, this will cause errors. A quick null test before the increment should sort it out.

if (Session["PagesViewed"] != null)
    Session["PagesViewed"] = ((int)Session["PagesViewed"]) + 1;

Answer 2

Session["PagesViewed"] will only return an Object - which is why your .ToString() call works. You will need to cast this back to an int, increment it there, then put it back in the session.

Answer 3

Yes, it can be. However, ++ only works when the compiler knows the object is an int. How does it know that some other part of your code doesn't sneakily do Session["PagesViewed"] = "Ha-ha"; ?

You can effectively tell the compiler that you won't do something like that by casting: you'll get a runtime exception if the session variable isn't really an int.

int pagesViewed = (int)Session["PagesViewed"];
if (pagesViewed == 2)
{
    pagesViewed = 0;
}
else
{
    pagesViewed++;
}
Session["PagesViewed"] = pagesViewed;