C#

Articles about coding with C# in .NET projects.

C# – How to create a custom exception

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To create a custom exception, create a subclass of the Exception class, like this: Then throw it just like you would any other exception, like this: It’s a good idea to call the base constructor from your constructor and pass in your custom error message. If this exception is unhandled, or if you are logging … Read more

.NET Core – Check which OS you’re running in

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.NET Core enables you to write cross-platform C# code. Sometimes you’ll want to do things differently depending on the OS you’re running in. You can use RuntimeInformation.IsOSPlatform() to figure out which OS you’re in. Here’s an example of using this to see if you’re running in Windows: Example – Loading a different native library depending … Read more

C# – Using the DynamicData attribute in unit tests

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The purpose of parameterized tests is to eliminate duplicated tests. There are two ways to pass parameters into a parameterized test: the DataRow attribute and the DynamicData attribute. With DataRow, the problem is you can only pass in constants and arrays. You can’t pass in reference types. When you try to pass in reference types, … Read more

C# – Thread-safe bool properties using Locks vs Interlocked

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The following bool property is not thread-safe. Why is this thread un-safe? Let’s say you have two threads running at the same time. One thread is reading the bool property, while the other thread is changing the value from false to true. It’s possible for the reader thread to get the stale value (false instead … Read more

C# – ManualResetEventSlim and AutoResetEvent

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When you want thread(s) to wait until they’re signaled before continuing, there are two simple options: I’ll show examples of using both of these. ManualResetEventSlim examples ManualResetEventSlim is like waving a flag at a car race. All race cars (threads) line up at the starting line and wait for the flag, and then they all … Read more

C# – How to use format strings with string interpolation

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Interpolated strings have the following structure: {variable:format}. Typically you exclude the format, so they normally look like this: $”My name is {name}”. Here’s how to use format strings with an interpolated string: This outputs the following: This is the equivalent of using string.Format() like this: Read more about why you should use string interpolation instead … Read more

Serializer options cannot be changed once serialization or deserialization has occurred

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Problem When using System.Text.Json, it’s a good idea to reuse JsonSerializerOptions objects. This leads to a massive 200x speedup in subsequent calls to the serializer. The downside is you can’t change properties on the options object after you’ve passed it in a Serialize()/Deserialize() call. You’ll get the exception: System.InvalidOperationException: Serializer options cannot be changed once … Read more

C# – Handle a faulted Task’s exception

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When a Task throws an exception and stops running, it has faulted. The question is, how do you get the exception that was thrown from the faulted Task? This depends on if you’re awaiting the Task or not. This article shows how to handle a faulted Task’s exception in two scenarios: when you’re awaiting the … Read more

C# – Get a file’s checksum using any hashing algorithm

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This article shows how to get a file’s checksum using any of these hashing algorithms: MD5, SHA1, SHA256, SHA384, and SHA512. If you are only interested getting a specific type of checksum, take a look at the first section. If you’re interested in a general-purpose checksum method that allows you to generate the checksum using … Read more

C# – Check if an IP range is valid

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Given an IP range as a starting IP address and an ending IP address (as strings, like from user input or a config file), you can check if the IP range is valid by doing the following steps: Here’s an example. Let’s say you’re given starting IP “192.168.0.1” and ending “192.168.0.11”. The following table shows … Read more

How to add User Secrets in a .NET Core console app

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The User Secrets feature in .NET is a safe, simple way to override values in appsettings.json. The overridden values only exist in a file sitting in your own dev environment, so you don’t accidently commit them to your source control repository. This feature is enabled in ASP.NET by default, and the framework does most of … Read more

C# – Set operations with Linq

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In this article, I’ll explain four set operations – intersection, union, difference, and symmetric difference – and how to perform these operations using Linq methods (such as Intersect()). These methods work on any type that implements IEnumerable – such as lists, arrays, and sets. Set intersection with Intersect() The intersection of set A {1,2} and … Read more

Invoke or BeginInvoke cannot be called on a control until the window handle has been created

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Problem In a WinForms project, if you try to call Invoke/BeginInvoke before the window handle is created, you’ll get the following exception: System.InvalidOperationException: Invoke or BeginInvoke cannot be called on a control until the window handle has been created Because this exception happens while the form is initializing, it typically results in the form not … Read more

NLog – Split trace logging into its own file

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This article explains how to configure NLog so that trace-level log messages go to their own file. This is useful because trace logging involves logging every method call for short-term troubleshooting, leading to very large log files. This approach only requires modifying the nlog.config file, and doesn’t require any code changes. In the end, all … Read more

C# – Switch from using HttpWebRequest to HttpClient

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There are many reasons to use HttpClient instead of HttpWebRequest. For one, the MSDN docs strongly recommends against using HttpWebRequest, and using HttpClient instead. That should be enough, but if you need a little more convincing, take a look at the Practical reasons to not use HttpWebRequest section below. In addition to explaining why not … Read more

C# – How to read configuration from appsettings.json

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The appsettings.json file is a convenient way to store and retrieve your application’s configuration. You can add it to any project and then use the Microsoft.Extensions.Configuration library to work with it. Since appsettings.json is just a JSON file, you can add any section / values you want (this is easier than working with XML-based app.config … Read more

C# – Duplicate ‘AssemblyVersion’ attribute

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Problem You’re trying to add the AssemblyVersion attribute to your project, like this (or perhaps you’re trying to auto-increment the version): And you get the following compiler errors: Error CS0579 Duplicate ‘AssemblyVersion’ attribute Error CS0579 Duplicate ‘AssemblyFileVersion’ attribute But you don’t see these attributes anywhere else in your project. Solution The problem is Visual Studio … Read more

How to generate XML documentation and include it in a nuget package

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XML documentation comments serve two purposes: In this article I’ll show how to automatically generate an XML documentation file and how to include it in a nuget package. 1 – Write the XML documentation comments in your code I have a method called MergeInPlace() (which merges two dictionaries in-place). To explain what this is doing … Read more

C# – Read a custom config section from app.config

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In this this article, I’ll show the simplest to get a custom config section from app.config and load it into your own config class. You can implement IConfigurationSectionHandler and use ConfigurationManager.GetSection() to do this. I’ll show the steps below. 1 – Add a custom config class The first step is to create a class that’ll … Read more

C# – Merge two dictionaries in-place

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When you merge two dictionaries, you can either merge them in-place, or create a new dictionary and copy the values over to it. The following extension method does an in-place merge of two dictionaries. It loops through items in the right dictionary, adding them to the left dictionary. When duplicate keys exist, it’s keeping the … Read more

How to use toxiproxy to simulate web API error scenarios

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When you have code that calls an endpoint, you need to make sure it’s resilient and can handle error scenarios, such as timeouts. One way to prove your code is resilient is by using toxiproxy to simulate bad behavior. Toxiproxy sits between your client code and the endpoint. It receives requests from your client, applies … Read more

C# – Fill a dropdown with enum values

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When you need to show enum values in a dropdown (ComboBox control with DropDownStyle=DropDown), it’s a good idea to automatically populate the list, instead of manually setting all of the values. To fill the dropdown with the enum’s values, set the DataSource to Enum.Values(), like this: Read more about how to show the enum’s Description … Read more

System.BadImageFormatException: Could not load file or assembly

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Problem – Can’t load assembly When you have one assembly trying to use another assembly, and they don’t have matching bitness (x64 or x86), then you’ll get an exception: either BadImageFormatException or FileLoadException. If your project references another assembly, and the bitness doesn’t match, you’ll get this exception: System.BadImageFormatException: ‘Could not load file or assembly … Read more