Multicast delegates

Context: Delegates can hold multiple methods using the + and - operators. Invoking a multicast delegate calls all methods in order.

public delegate void Notify(string message);

public static void LogToFile(string msg) => Console.WriteLine($"File: {msg}");
public static void LogToConsole(string msg) => Console.WriteLine($"Console: {msg}");

Notify logger = LogToFile;
logger += LogToConsole; // add second method

logger("Hello"); // both methods are called

Removing methods

logger -= LogToFile; // removes first method
logger("Only console");

Return values

For multicast delegates with non‑void return, only the last method’s return value is kept. Use GetInvocationList() to process all.

foreach (Notify n in logger.GetInvocationList())
{
    n("Processing");
}

Real-world usage example

Event notifications: Multiple subscribers to an event are stored as a multicast delegate. Raising the event notifies all subscribers.

Example: In ASP.NET Core, the IApplicationLifetime events use multicast delegates.

Related sections

• 7.1 Delegates
• 7.2 Events