What is NullReferenceException?

NullReferenceException is a runtime exception in C# that occurs when you try to access members of an empty object. This can happen when:

• Try calling the method of an empty object.
• Try to access the properties of an empty object.
• Try to dereference a null pointer.

How to solve it?

There are several ways to solve NullReferenceException:

• Check for empty values ​​before accessing members. Always check whether the object is empty before accessing any member of the object. You can use the if statement as shown in the following example:

if (object != null)
{
    // 访问对象的成员。
}

• Use the empty merge operator. The empty merge operator (??) allows you to specify the default value to use if the object is empty. For example, the following code returns the value of the Name property if the object is not empty; if the object is empty, it returns "Unknown":

string name = object?.Name ?? "Unknown";

• Use the empty condition operator. The empty condition operators (?. and ?[]) allow you to access members of an object without checking null values ​​beforehand. For example, the following code returns the value of the Name property if the object is not empty; if the object is empty, it returns null:

string name = object?.Name;

• Use the try/catch block. You can also use the try/catch block to handle NullReferenceExceptions. For example, the following code will process NullReferenceException and print a message to the console:

try
{
    // 访问对象的成员。
}
catch (NullReferenceException ex)
{
    Console.WriteLine("NullReferenceException 发生。");
}