What is NullReferenceException in C#?
In C# programming language, when we attempt to access a member (method, property, or field) of an object that is currently set to null, we will receive an exception called the NullReferenceException. This occurs because a null reference does not point to any memory address, so trying to access a null reference’s members throws an exception.
There are some of the few scenarios that demonstrate how the NullReferenceException can occur and how to manage it:
- Accessing a property of a null object
- Calling a method on a null object
Accessing a property of a null object
In this scenario, we will attempt to access a property of an object, and the object is currently initiated to null.
public class MyTestClass{public int MyTestProperty { get; set; }}public class Program{public static void Main(){MyTestClass myTestObj = null;int value = myTestObj.MyTestProperty; // This line will throw a NullReferenceException}}
The MyTestClass class is created in the aforementioned code, and it has a property called MyTestProperty. The attempt to use the MyTestProperty property after initializing myTestObj to null will result in a NullReferenceException.
Before accessing an object’s members, we should check to see if it’s not null. We can handle the situation as in the example below:
public class Program{public static void Main(){MyTestClass myTestObj = null;if (myTestObj != null){int value = myTestObj.MyTestProperty;// Do something with 'value'}else{// Handle the case when myTestObj is nullConsole.WriteLine("myTestObj is null.");}}}
Calling a method on a null object
Now, we will attempt to call a method on a null object.
using System;public class MyTestClass{public void MyTestMethod(){Console.WriteLine("Hello World!");}}public class Program{public static void Main(){MyTestClass myTestObj = null;myTestObj.MyTestMethod(); // This line will throw a NullReferenceException}}
The coding example above uses a class called the MyTestClass and a method named the MyTestMethod. When we try to invoke the MyTestMethod method after setting myTestObj to null, a NullReferenceException is raised.
Before accessing an object’s members, we should again check to see if it’s not null. We can handle this situation as in the example below:
public class Program{public static void Main(){MyTestClass myTestObj = null;if (myTestObj != null){myTestObj.MyTestMethod();}else{// Handle the case when myTestObj is nullConsole.WriteLine("myTestObj is null.");}}}
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