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Each dictionary key maps to exactly one value. When you want multiple values per key, you can use a dictionary of lists. Here’s an example of creating a dictionary of lists, where each key maps to multiple ints: Notice that you can add to the dictionary like normal. The difference with a dictionary of lists … Read more
You can use dictionaries with tuples as the keys or values. I’ll show examples below. Dictionary with tuple as key Tuples have two or more fields, so using a tuple as the key is a simple way to have compound keys in a dictionary. Here’s an example of creating a dictionary with a named tuple … Read more
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
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
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
In .NET 5 and above, you can loop through a dictionary and directly change its values. Here’s an example: This outputs the following: You couldn’t do this before .NET 5, because it would invalidate the enumerator and throw an exception: InvalidOperationException: Collection was modified; enumeration operation my not execute. Instead, you’d have to make the … Read more
The simplest way to convert a list to a dictionary is to use the Linq ToDictionary() method: This loops through the list and uses the key/element selector lambdas you passed in to build the dictionary. In this article, I’ll go into details about how to use ToDictionary() and show how to deal with duplicate keys. … Read more
By default, System.Text.Json.JsonSerializer only serializes public properties. If you want to serialize non-public properties, you have two options: In this article, I’ll show examples of both approaches for handling non-public properties. Updated 2022-02-22 to explain the new JsonInclude attribute added in .NET 5. Write a custom JSON converter to serialize non-public properties When the built-in … Read more
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
Before .NET 5, the built-in JSON serializer (System.Text.Json) couldn’t handle serializing a dictionary unless it had a string key. Here’s an example running in .NET Core 3.1 to show the problem. This is initializing a dictionary with values and then attempting to serialize it. This results in exception: System.NotSupportedException: The collection type ‘System.Collections.Generic.Dictionary`2[System.Int32,System.String]’ is not … Read more
A default constructor is a constructor that doesn’t have parameters. Therefore, to check if a type has a default constructor, you can use reflection to loop through the constructors and see if there are any with no parameters, like this: In this article I’ll show an example of loading types that implement a specific interface … Read more
You can use reflection to get all classes in the current assembly that implement a specific interface. Here’s how: To create instances of these types, loop through them and use Activator.CreateInstance(), like so: Example – Auto-wire a command routing table Let’s say we want to build a command routing table. We have commands and want … Read more