Lesson 10 of 40 Core C# Intermediate ⏱ 30 min

Exception Handling & Error Patterns

Write robust code with try/catch/finally, custom exceptions, the Result pattern, and modern global exception filters.

Part 1: try / catch / finally

try
{
    var data = await FetchDataAsync(url);
    Process(data);
}
catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.NotFound)
{
    _logger.LogWarning("Resource not found: {Url}", url);
}
catch (Exception ex)
{
    _logger.LogError(ex, "Unexpected error");
    throw; // Re-throw preserving stack trace
}
finally
{
    Cleanup(); // Always runs
}

Part 2: Custom Exceptions

public class OrderNotFoundException : Exception
{
    public int OrderId { get; }
    public OrderNotFoundException(int id)
        : base($"Order {id} not found") => OrderId = id;
}

// Throw it
throw new OrderNotFoundException(orderId);

Part 3: Result Pattern (No Exceptions for Flow)

public readonly record struct Result<T>
{
    public bool IsSuccess { get; }
    public T? Value { get; }
    public string? Error { get; }
    public static Result<T> Ok(T v) => new() { IsSuccess=true,Value=v };
    public static Result<T> Fail(string e) => new() { Error=e };
}

Part 4: IDisposable & using Statements

// using ensures Dispose() is called
using var conn = new SqlConnection(connStr);
await conn.OpenAsync();
// conn.Dispose() called at end of scope automatically

// Implement IDisposable in your own classes
public class FileWriter : IDisposable
{
private readonly StreamWriter _writer;
public void Dispose() => _writer.Dispose();
}

Exception Handling & Error Patterns

Part 1: try / catch / finally

Part 2: Custom Exceptions

Part 3: Result Pattern (No Exceptions for Flow)

Part 4: IDisposable & using Statements

C# in Visual Studio 2026