How I Learned From Class Into My - amazonia.fiocruz.br

How I Learned From Class Into My Video

Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. You are trying to use something that is null or Nothing in VB. This means you either set it to nullor you never set it to anything at all. Like anything else, null gets passed around. If it is null in method "A", it could be that method "B" passed a null to method "A".

The rest of this article goes into more detail and shows mistakes that many programmers often make which can lead to a NullReferenceException. The runtime throwing a NullReferenceException always means the same thing: you are trying to use a reference, and the reference is not initialized or it M once initialized, but is no longer initialized.

Bottom Line

This means the reference is nulland you cannot access members such as methods through a null reference. The simplest case:. This will throw a NullReferenceException at the second line because you can't call the instance method ToUpper on a string reference pointing to null.

How do you find the source of a NullReferenceException? Apart from looking at the exception itself, which will be thrown exactly at the location where it occurs, the general rules of debugging in Visual Studio apply: place strategic breakpoints and inspect your variableseither by hovering the mouse over their names, opening a Quick Watch window or using the various debugging panels like Locals and Autos. If you want to find out where the reference is or isn't set, right-click its name and select "Find All References". You can then place a breakpoint at every found location and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether you expect the reference to be non-null, inspect the variable, and verify that it points to an instance when you expect it to. By following the program flow this way, you can find the location where the instance should not be null, and why it isn't properly set.

If ref1 or ref2 or ref3 is null, then you'll get a NullReferenceException. If you want to solve the problem, then find out which one is null by rewriting the expression to its simpler equivalent:. How I Learned From Class Into My, in HttpContext.

Your Answer

NameHkw HttpContext. Current could be null, or the User property could be null, or the Identity property could be null. If you want to avoid the child Person null reference, you could initialize it in the parent Book object's constructor.

While the new keyword is used, it only creates a new instance of Bookbut not a new instance of Personso the Author the property is still null.

The new Person only creates an instance of Personbut the Books collection is still null. The collection Initializer syntax does not create a collection for p1. Booksit only translates to the p1. Note: The VB. NET compiler inserts null checks for event usage, so it's not necessary to check events for Nothing in VB.]