如何处理int类型的会话变量中的null

Question

If the session["Colindex"] is null. It throws a error msg saying that Object reference not set to null.

int colid =(int) Session["ColIndex"];

Any help is appreciated

Answer 1

Use C# ?? null coalescing operator:

int colid = (int)(Session["ColIndex"] ?? 0);

This will set colid to the value in Session, or 0 if it's null.

Answer 2

If the Session["ColIndex"] has yet to be created, then there is no value. As Session is a reference variable, there is no reference to the instance of the object on the heap which is why you are receiving the " Object reference not set to an instance of an object " error. In other words, the Session variable was never assigned/created.

You'll need to test for null before casting your session:

if ( Session["ColIndex"] != null )
{
  int colid = (int)Session["ColIndex"];
  // do other stuff
}

Answer 3

我不知道这是什么语言，但是您可能需要在转换为int之前测试null。