Testing a session variable for null or empty space

问题

What I currently have is this:

if ((string)Session["PlanID"] == null)
{
   string PlanID = Request.QueryString["PlanID"];
   Session["PlanID"] = PlanID;
}

What I need is something like this:

if ((string)Session["PlanID"] == null) or if ((string)Session["PlanID"] == "")
{
   string PlanID = Request.QueryString["PlanID"];
   Session["PlanID"] = PlanID;
}

How would I do that?

回答1:

You can use IsNullOrEmpty from string.

if (string.IsNullOrEmpty((string)Session["PlanID"])) {
   string PlanID = Request.QueryString["PlanID"];
   Session["PlanID"] = PlanID;
}

回答2:

You can use the String.IsNullOrWhiteSpace Method.

This method also checks for null values

Indicates whether a specified string is null, empty, or consists only of white-space characters.

if (string.IsNullOrWhiteSpace((string)Session["PlanID"]))
{
   string PlanID = Request.QueryString["PlanID"];
   Session["PlanID"] = PlanID;
}

来源：https://stackoverflow.com/questions/41989625/testing-a-session-variable-for-null-or-empty-space