A null string might be something you just ignore and move on. Not running a SQL query would be a serious problem for your application.
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For example, in the code below, the SqlCommand object is never initialized. You can also have null reference exceptions because any type of object is null. You can’t call ToUpper() on a null string. The following code will throw a NullReferenceException if the variable “text” being passed in is null. Here are some ways to avoid NullReferenceException. They are usually very simple problems caused by not adding additional logic to ensure that objects have valid values before using them. Null reference errors are responsible for a good percentage of all application bugs. > Understanding the NullReferenceException When you try to call a method or another member on the said variable, you got the NullReferenceException. These variables can point to “nothing”, though, and that’s what we call a null reference: a reference that doesn’t point to any object. So, a reference is what a variable of a reference type contains. Types such as int (and the other numerical primitive types), DateTime, and boolean are value types.
If it helps you visualize it better, you can think of a reference as a linking pointing to a web page, or a shortcut pointing to a file on your computer. They hold a reference that points to where the object lives in memory. Reference types variables, on the other hand, don’t hold the value itself. If you have a variable of a value type, it stores the value itself. NET, you can divide data types in two categories: value types and reference types. But what is a null reference? In what way does it differ from a non-null reference? We already know that the NullReferenceException is caused by a null reference.
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At this point, you’re halfway there to seeing the whole picture.Īfter this round of theoretical definitions, we’ll get to more practical matters, teaching you how to avoid the NullReferenceException in practice. After that, you’ll learn what null references are. We’ll start with fundamentals, by giving a brief explanation of what references are in C#/.NET.
This exception is thrown when you try to access a member-for instance, a method or a property-on a variable that currently holds a null reference.īut what is a null reference? What are “references” in the first place? How can you stop the NullReferenceException from happening in your code? That’s what we’re going to cover in today’s post. This infamous and dreaded error message happens when you get a NullReferenceException. “Object Reference Not Set to an instance of an object.” Cast the first stone those who never struggled with this error message when they were a beginner C#/.NET programmer.
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