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C# – Validate an IP address

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Use IPAddress.Parse() to parse an IP address from a string. This handles both IPv4 and IPv6 addresses and throws an exception if the string can’t be parsed into a valid IP address. Here’s an example: This outputs the following: Use IPAddress.TryParse() if you don’t want exceptions to be thrown. It returns false if the string … Read more

ASP.NET Core – Client-side custom validation attributes

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I wrote about how to add custom validation attributes. These are used for model validation on the server-side. You can also use these for client-side validation, which I’ll show in this article. 1 – Implement IClientModelValidator The first step is to implement the IClientModelValidator interface in the custom validation attribute class. This has a single … Read more

C# – ConfigurationSection.Get() returns null

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When you use ConfigurationSection.Get() to load an object from appsettings.json, it returns null if the section doesn’t exist. Since you’re probably not expecting this to be null, this can lead to problems surfacing in unexpected places, such as getting a NullReferenceException: Note: If you’re using ASP.NET Core, you’ll be referring to the config via builder.Configuration … Read more

C# – How to read problem details JSON with HttpClient

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Problem details (RFC7807) is a standardized error response format that has a Content-Type of application/problem+json, an error response code (i.e. 400 – Bad Request), and has a response body that looks like this: This can be extended to include any number of properties. The example shown above comes from the default way ASP.NET Core returns … Read more

C# – How to unit test a model validation attribute

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You can unit test a validation attribute by creating an instance of it and then testing the two methods: In this article, I’ll show examples of unit testing these methods in a custom validation attribute and in a built-in validation attribute (i.e. [Range]). Unit testing a custom validation attribute Consider the following custom validation attribute … Read more

ASP.NET Core – Create a custom model validation attribute

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There are many built-in model validation attributes available – such as [Required] and [Range] – which you can use to handle most validation scenarios. When these aren’t sufficient, you can create a custom validation attribute with your own validation logic. I’ll show an example of how to do that. 1 – Subclass ValidationAttribute and implement … Read more

C# – How to implement GetHashCode() and Equals()

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The simplest way to implement GetHashCode() is to use the built-in System.HashCode.Combine() method and pick the properties you want to include. Let it do the work for you. Furthermore, the simplest way to implement Equals() is to use the is operator and compare all the properties. Here’s an example: Note: Use (Title, Year).GetHashCode() in versions … Read more

C# – Using the ‘not’, ‘and’, ‘or’ operators

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I’ll show examples of using the pattern matching operators – ‘not’, ‘and’, ‘or‘ – with the is operator. These are nice syntax sugar that make conditional logic a bit easier to read. Note: ‘not’, ‘and’, ‘or’ were added in C# 9. ‘not’ operator Here’s an example of the not operator: This is checking if the … Read more

C# – Check if a nullable bool is true

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You can’t use nullable bools (bool?) exactly like regular bools, because they aren’t the same thing. When you try to use them like regular bools, you run into compiler errors and runtime exceptions. Instead, you have to explicitly compare the nullable bool with true/false. Here’s an example of checking if a nullable bool is true … Read more

C# – Hex string to byte array

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This article shows code for converting a hex string to a byte array, unit tests, and a speed comparison. First, this diagram shows the algorithm for converting a hex string to a byte array. To convert a hex string to a byte array, you need to loop through the hex string and convert two characters … Read more