Lỗi call to a member function nullable on null năm 2024
When you have a statement like Show
To figure out what's wrong there, you can set a breakpoint on the same line, start debugging and then when the breakpoint hits, just check the value of A, B or E. When NullReferenceException happens?There are some common cases that you may encounter a NullReferenceException. Here is a summary based on NllReferenceEexception article in .NET documentations. I've put the link of the article in the next section in the answer, where you can find some useful example as well. A NullReferenceException exception is thrown when you try to access a member on a type whose value is null. A NullReferenceException exception typically reflects developer error and is thrown in the following scenarios: A
1 occurs when an invalid argument is passed to a method in C#. In this case, it refers to the passing of a null object when the method expects a non-null object or a value. Similar to other exceptions raised as a result of arguments,
1 is not generally raised by the
3 framework itself or the Common Language Runtime (CLR). Instead, it is thrown by an application or a library as an indication of improper null arguments. Syntax of ArgumentNullExceptionSimilar to any class or method, exceptions also have their own syntax. Below is the syntax for ArgumentNullException:
The
4comes under the class of
5, which is inherited from the
6 class. The
6 class is in turn inherited from the
8 class, which is inherited from the
9 class.
When does the ArgumentNullException occur in C#?Generally, there are two major circumstances when an
0 is thrown, both of which reflect developer errors:
Example One: Working with an Inbuilt Function like Parse()In the below code, we are trying to parse and convert a string value to an integer value, assuming that the string is valid and contains only numbers.
Output of Example 1We can see that
1 is causing the error because its parameter should not be null.
Example Two: Dealing with Custom ClassesIn the below code we have created a class
2, two private strings,
3 and
4, and used them for the public properties of
5and
6respectively. Then we wrote custom
7 and
8 functions that checked whether or not the passed argument value was null. If true, we throw in a new
1 instead of passing the entire message, as is frequently the case,
1 expects just the name of the argument, which should not be null.
Output of Example TwoWhen the above code is run we get the following output:
The parameter
1 is causing this exception as its value should not be null. How to Handle ArgumentNullException in C#Now let’s see how to debug and handle this exception in C#. The best approach is to use
2 block and perform a simple check before passing the values. Let’s see how to fix both examples discussed earlier. How to Fix Example One:On observing the first few lines of the output from the bottom to the top, it is quite evident that when parsing a string to convert the string to a number,
1 occurs as the argument of
4cannot be null.
Working Code:
Output:
How to Fix Example Two:Implement a
2 block in this case because the value is being checked in the
6method. Working Code:
Output:
0 Avoiding ArgumentNullExceptionsTo summarize, an
0 comes from
8 when an invalid argument is passed to a method. In this case, it refers to passing a null object when the method expects a non-null object or a value. Furthermore, whenever dealing with
9, it’s always good practice to perform a
0 and then pass any arguments. Track, Analyze and Manage Errors With RollbarManaging errors and exceptions in your code is challenging. It can make deploying production code an unnerving experience. Being able to track, analyze, and manage errors in real-time can help you proceed with more confidence. Rollbar automates error monitoring and triaging, making fixing C# errors easier than ever. Sign Up Today! |