C# – Convert a dictionary to a list

The simplest way to convert a dictionary to a list is by using the Linq ToList() method, like this: When used on a dictionary, ToList() returns a list of KeyValuePair objects. This example outputs the following: Dictionary keys to list If you want a list of the dictionary’s keys, use ToList() on Dictionary.Keys, like this: … Read more

C# – Get dictionary key by value

Dictionaries have keys mapped to values, which enables you to efficiently lookup values by key. But you can also do a reverse lookup: get the key associated with a value. The simplest option is to use FirstOrDefault(), but that’s only a good idea if you know the value exists for sure. Instead, the best option … Read more

C# – Check if key exists in dictionary

When you want to check if a key exists, use Dictionary.ContainsKey(). This returns true if the key exists and otherwise returns false. Here’s an example: This initializes the dictionary with a few items and then checks if one of the key exists. This outputs: Usually you’ll want to do something based on if the key … Read more

C# – Update value in a dictionary

After you add a key/value pair to a dictionary, you can update the value for the key by using the indexer syntax (i.e. dictionary[key]=value), like this: This outputs the updated value for the ‘Bob’ key: The indexer syntax inserts if the key doesn’t exist -or- updates the value if the key already exists. This means … Read more

System.ArgumentException: An item with the same key has already been added

Problem Dictionaries require keys to be unique. When you try to add a key/value to a dictionary and the key already exists, you get the following exception: System.ArgumentException: An item with the same key has already been added. This can happen when you use Dictionary.Add() or when you initialize a dictionary using the “curly brace” … Read more

C# – Get value from dictionary

Dictionaries store key/value pairs. When you want to get the value for a key, you can use the indexer syntax and specify the key, like this: Note: In order to show how to get a value, I had to initialize the dictionary with key/value pairs. This returns the value associated with the “Bob” key and … Read more

C# – Add to a dictionary

The simplest way to add a key/value pair to a dictionary is by using Dictionary.Add(), like this: If the key already exists, Dictionary.Add() throws an ArgumentException because the key must be unique. There are a few other ways to add to a dictionary in different scenarios, which I’ll explain below. Add or update key/value in … Read more

C# – Validate an IP address

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

C# – Ignore case with string.Contains()

By default, string.Contains() does a case sensitive search for a substring (or character) in a string. You can make it do a case insensitive search instead by passing in StringComparison.OrdinalIgnoreCase, like this: Note: StringComparison has three ‘ignore case’ options to choose from. Because this is doing a case insensitive search, it matched “earth” to “Earth” … Read more

C# – Convert a string to an int

There are three ways to convert a string to an int: I’ll show examples of using these approaches. Use int.Parse() int.Parse() takes a string and converts it to a 32-bit integer. Here’s an example of using int.Parse(): When conversion fails int.Parse() throws an exception if it can’t convert the string to an int. There are … Read more

C# – How to convert char to int

Converting a char to an int means getting the numeric value that the char represents (i.e. ‘1’ to 1). This is not the same as casting the char to an int, which gives you the char’s underlying value (i.e. ‘1’ is 49). There are three ways to convert a char to an int: I’ll show … Read more

C# – Convert a List to a string

There are two good ways to convert a List<T> to a string: I’ll show examples of both approaches. Using String.Join() String.Join() is the simplest way to convert a List to a string. With this method, you pass in the List and a delimiter and it outputs a string. You can use any delimiter you want. … Read more

OverflowException: Value was either too large or too small for an int32

Problem When you try to convert a string to an integer with int.Parse() (or Convert.ToInt32()), you get the following exception: System.OverflowException: Value was either too large or too small for an Int32. The problem is the integer value in the string can’t fit in the 32-bit integer. Int32 (int) can only hold values between -2147483648 … Read more

ASP.NET Core – Client-side custom validation attributes

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

ASP.NET Core – Control the graceful shutdown time for background services

ASP.NET Core gives you a chance to gracefully shutdown your background services (such as cleaning up and/or finishing in-progress work). By default, you’re given a grand total of 5 seconds to shutdown all background services. If you need more time than this, there are a few ways to control the graceful shutdown time, which I’ll … Read more

How to debug .NET source code in Visual Studio

When you’re using the Visual Studio debugger to step through your code, sometimes it’s useful to be able to step into the .NET source code. I had to do this recently to figure out why my ASP.NET Core code wasn’t behaving as expected. You can enable .NET source code debugging with the following steps: Now … Read more

C# – How to create directories

You can use Directory.CreateDirectory() to create a directory at the specified path (absolute or relative), like this: This creates the directory if it doesn’t exist, otherwise it does nothing. That means you don’t need to check if the directory exists before calling Directory.CreateDirectory(). In this article, I’ll go into more details about using Directory.CreateDirectory(). CreateDirectory() … Read more

ASP.NET Core – How to manually validate a model in a controller

Manually validating a model can mean a few different things. It depends on what you’re trying to do exactly. Are you trying to validate a model object against its validation attributes? Use TryValidateModel(). Are you trying to do validation logic manually (instead of using validation attributes)? You can add errors to ModelState in that case. … Read more

ASP.NET Core – How to unit test a custom InputFormatter

In this article, I’ll show how to unit test a custom InputFormatter. The main thing to test is the output of the ReadRequestBodyAsync() method. To test this, you have to pass in an InputFormatterContext object containing the request body. As an example, I’ll show how to unit test the following ReadRequestBodyAync() method: Note: This parses … Read more

ASP.NET Core – Add a custom InputFormatter

Input formatters are used to deserialize the request body to a model object (which is then passed into an action method). There are built-in input formatters for handling JSON and XML. You can add your own input formatter when you want to customize request body deserialization. There are two scenarios where a custom InputFormatter would … Read more

C# – Manually validate objects that have model validation attributes

You can use the Validator utility class to do manual attribute-based validation on any object, in any project type (as opposed to doing automatic model validation in ASP.NET). To do this, add model validation attributes to your class properties, then create an object and populate it (aka binding), and finally execute manual validation with the … Read more

C# – ConfigurationSection.Get() returns null

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# – Parsing a CSV file

In this article, I’ll show how to parse a CSV file manually and with a parser library (CsvHelper). Let’s say you have the following CSV file: To manually parse this, read the file line by line and split each line with a comma. This gives you a string array containing the fields that you can … Read more

C# – How to disable ModelStateInvalidFilter

There are two options for disabling ModelStateInvalidFilter: You’d do this when you want to manually perform model validation. I’ll show both options below. Disable ModelStateInvalidFilter globally To disable ModelStateInvalidFilter for *all* actions, set SuppressModelStateInvalidFilter=true in ConfigureApiBehaviorOptions, like this: Disable ModelStateInvalidFilter for specific actions To disable ModelStateInvalidFilter selectively, you can implement an IActionModelConvention attribute that removes … Read more

C# – How to treat warnings like errors

Warnings are easy to ignore and forget about, which isn’t good. They point out potential problems that you might want to fix. To make it easier to pay attention to warnings, you can treat them like errors. You can choose which warnings to treat like errors by using settings in the project file (or in … Read more