You can also compare a variable of a nullable value type with null instead of using the HasValue property, as the following example shows:. If you want to assign a value of a nullable value type to a non-nullable value type variable, you might need to specify the value to be assigned in place of null. Use the null-coalescing operator?? GetValueOrDefault T method for the same purpose :. GetValueOrDefault method. You can also explicitly cast a nullable value type to a non-nullable type, as the following example shows:.
At run time, if the value of a nullable value type is null , the explicit cast throws an InvalidOperationException.
A non-nullable value type T is implicitly convertible to the corresponding nullable value type T? The predefined unary and binary operators or any overloaded operators that are supported by a value type T are also supported by the corresponding nullable value type T?
These operators, also known as lifted operators , produce null if one or both operands are null ; otherwise, the operator uses the contained values of its operands to calculate the result. For the bool? For more information, see the Nullable Boolean logical operators section of the Boolean logical operators article.
The following example shows that 10 is. For the inequality operator! If there exists a user-defined conversion between two value types, the same conversion can also be used between the corresponding nullable value types. An instance of a nullable value type T? From where do you call this code? You should never place a dependency on Session within a class other than the page class or a class specifically designed to manage Session variables.
If this class requires data then pass the data to the class via a constructor or property. This designs allows the class to be shared among many projects. IRequiresSessionState, you can access how you access in cs class file.
Your code seems fine, are you sure that the above code caused this problem? I suspect that your other code caused this problem, please debug your code and check which statement caused the problem. Besides, you could debug your code and check the value of the HttpContext. Session, and you'd better to use the following code to replace your code.
The Session is page property and it cannot be used outside the Page class or in static method so you have get reference of Session object from the context via HttpContext. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How to check if session value is null or session key does not exist in asp.
Asked 4 years, 11 months ago. Active 7 months ago. Viewed 47k times. Unbreakable Unbreakable 6, 18 18 gold badges 66 66 silver badges bronze badges. Roma : Thank you. You rock! You might want to learn how to program before trying to program? There are some good books out there that you can read and will help you out greatly. Will: I want to code and learn together.
I want to do more practicals. Still thanks for your inputs. Will: I am a beginner so I do silly mistakes. Add a comment.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What is the best way to determine a session variable is null or empty in C? Ask Question.
Asked 13 years, 2 months ago. Active 1 year, 11 months ago. Viewed k times. What is the best way to check for the existence of a session variable in ASP. NET C? Currently the only way I know of is: var session; if Session["variable"]!
Add a comment. Active Oldest Votes. To follow on from what others have said. I tend to have two layers: The core layer. Rob Cooper Rob Cooper 28k 25 25 gold badges silver badges bronze badges. Great approach! I have been using something similar for a long time, but hadn't incorporated generics. This avoids so many problems with different developers creating similar Session variables. Nice approach.
I'm having trouble implementing this in a C Class Library. That is pretty much how you do it. However, there is a shorter syntax you can use. Ely Ely 3, 1 1 gold badge 20 20 silver badges 18 18 bronze badges. Session["variable"] is an Object and the compiler will then convert it to a String because sSession is a String, if the Session["variable"] does not exist, it throws an exception!
You are absolutely correct.
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