C# – How to make a file read-only

There are two ways to programmatically make a file read-only: Here’s an example showing both ways to make a file read-only: Using File.SetAttributes() is useful when you want to manage all of file’s attributes at once. FileAttributes is an enum flag, so you can use bitwise operations to add/remove multiple attributes at once. That’s why … Read more

C# – How to set permissions for a directory (Windows only)

When you want to set permissions for a directory (and its files/subdirectories), you can use DirectoryInfo.GetAccessControl() to get the directory’s security, add/modify/remove access control rules, and then use DirectoryInfo.SetAccessControl() to apply the changes. Access control rules are a complex combination of different settings. They control being able to do things like creating a file in … Read more

C# – Search for files in a directory

Use Directory.EnumerateFiles() to search for files in a directory and then loop over the file paths (and then reading the files, or whatever you want to do with the info). Here’s an example of searching for files containing “hello” in the file name: Note: Use the wildcard character * to match anything. It returns an … Read more

C# – How to read a text file

The simplest way to read a text file is by using a high-level method in the .NET File API (in System.IO), such as File.ReadAllText(). These high-level methods abstract away the details of opening a file stream, reading it with StreamReader, and closing the file. Here’s an example of reading a text file’s content into a … Read more

C# – Parse a comma-separated string into a list of integers

Let’s say you want to parse a comma-separated string into a list of integers. For example, you have “1,2,3” and you want to parse it into [1,2,3]. This is different from parsing CSV with rows of comma-separated values. This is more straightforward. You can use string.Split(“,”) to get the individual string values and then convert … Read more

CsvHelper – Header with name not found

When your CSV header names don’t match your property names exactly, CsvHelper will throw an exception. For example, if your header name is “title” and your property name is “Title”, it’ll throw an exception like: HeaderValidationException: Header with name ‘Title'[0] was not found. If you don’t want to (or can’t) change the names to match, … 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# – Using CsvHelper when there’s no header row

When you’re parsing CSV with CsvHelper and there’s no header row, you have to configure it to map by field position. I’ll show how to do that. At the end, I’ll show the alternative approach of manually parsing in this scenario. Consider the following CSV data without a header row: Normally, CsvHelper maps fields to … 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# – Filter a dictionary

The simplest way to filter a dictionary is by using the Linq Where() + ToDictionary() methods. Here’s an example: Note: You can use the Dictionary constructor (new Dictionary<string, int>(filterList)) instead of ToDictionary() if you prefer. This produces a new dictionary with the filtered item: Where() produces a list (actually an IEnumerable) of KeyValuePair objects. Most … Read more

C# – Change a dictionary’s values in a foreach loop

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

C# – TimeZoneInfo with current UTC offset

TimeZoneInfo always shows the base UTC offset. This can be confusing because the UTC offset can change based on the date (due to daylight savings rules). Here’s an example showing DateTimeOffset and TimeZoneInfo with different offsets: You can get a date’s UTC offset from DateTimeOffset and combine it with TimeZoneInfo.DisplayName. This approach is implemented in … Read more

C# – How to use TimeZoneInfo

Time zones are complicated and their rules can change, so it makes sense to use a library when you’re dealing with them. One option in .NET is to use the built-in TimeZoneInfo class. Here’s an example of using TimeZoneInfo to get the local system’s time zone: This outputs: Note: The display name always show the … Read more

C# – Get key with the max value in a dictionary

The simplest way to get the key with the max value in a dictionary is to use the Linq MaxBy() method (added in .NET 6). This returns the key/value pair with the max value. Here’s an example: Note: All examples shown initialize the dictionary with a small number of key/value pairs for readability. This outputs … Read more

C# – Get the current date and time

Use DateTime.Now to get the current date/time, like this: This outputs the system’s current date/time: Note: By default, it uses the current culture’s date format (from the OS). This is showing the US date format – MM/dd/yyyy. DateTime.Now is the local date/time from the system where the code is executing. Keep that in mind if … Read more

C# – Loop through a dictionary

The simplest way to loop through a dictionary is with a foreach loop. Here’s an example of initializing a dictionary with values and then looping through it: This outputs the following: The loop variable is a KeyValuePair<string, int> with Key and Value properties. Instead of using this, you can deconstruct the KeyValuePair into named variables, … Read more

WinForms – Loop through a form’s controls

Forms also have a collection of controls (Controls property) that you can loop through. This is useful for when you want to do something to multiple controls and don’t want to have to manually type out code to deal with individual controls. Here’s an example of looping through a form’s top-level controls: Note: In the … Read more

C# – Check if a property is an enum with reflection

When you’re using reflection to look at a type’s properties, you can use PropertyInfo.PropertyType.IsEnum to check if the property is an enum. This is helpful when you want to be able to safely call an Enum API method (such as Enum.Parse()) on the reflected type, thus preventing an exception – ArgumentException: Type provided must be … Read more

WinForms – Bind controls to an object data source

Mapping classes to WinForm controls manually is probably the most tedious thing you can do in coding. In order to minimize this coding effort, you can bind your controls to an object data source. In this article, I’ll show how to do this in a WinForms App (.NET Core+) project. First, I’ll show step-by-step how … Read more

ASP.NET Core – How to get request headers

There are two ways to get request headers: When a request comes in, the framework loads request headers into the Request.Headers dictionary. You can use this just like any other dictionary. Here’s an example of using TryGetValue() to check if a request header exists and get its value: Note: To just check if a header … Read more

C# – Get subclass properties with reflection

When you use reflection to get properties, you can get just the subclass properties by using BindingFlags.DeclaredOnly (this causes it to exclude inherited properties). Here’s an example: Note: Use GetType() if you have an object. Use typeof() if you have a class. The code outputs just the subclass properties (from the Driver subclass): Get base … Read more

C# – Deserialize JSON using different property names

When JSON property names and class property names are different, and you can’t just change the names to match, you have three options: These options affect both deserialization and serialization. Let’s say you have the following JSON with camel-cased property names: Here’s an example of using the JsonPropertyName attribute: Note: The Newtonsoft equivalent is [JsonProperty(“title”)] … Read more

C# – How to use SortedSet

When you have a collection of elements that you’re continuing to add to, and need to keep the objects in sorted order at all times, you can use SortedSet. Internally, it uses a tree data structure to keep elements in sorted order (O(log n) insertion). This is far more efficient than repeatedly sorting a list … Read more

C# – How to ignore JSON deserialization errors

One error during JSON deserialization can cause the whole process to fail. Consider the following JSON. The second object has invalid data (can’t convert string to int), which will result in deserialization failing: With Newtonsoft, you can choose to ignore deserialization errors. To do that, pass in an error handling lambda in the settings: This … Read more