Explenation of delegates?

Question

I'm trying to develop a mod for Beat Saber, and I need to learn delegates and how to use them correctly. I looked at documentations and still, they don't make sense to me. All I know is something += anothersomething. So could someone please explain what delegates are used for, what situations they need to be used in, how to use them, and maybe some examples please. Thank you

Answer 1

@ToostR ，Welcome to Microsoft Q&A, based on your description, you have some questions about delegates.

The question When & why to use delegates? in stackoverflow is simliar to your problem and you could have a look.

So could someone please explain what delegates are used for

The first answer describes that By defining a delegate, you are saying to the user of your class, "Please feel free to assign any method that matches this signature to the delegate and it will be called each time my delegate is called".

how to use them, and maybe some examples please

You could refer to the second answer in the above link to guide you how to use delegate and it has a good code example to explain the delagate.

what situations they need to be used in

You could use the delegate when you meet one of the conditions:

1. You want to call series of method by using single delegate without writing lot of method calls.
2. You want to implement event based system elegantly.
3. You want to call two methods same in signature but reside in different classes.
4. You want to pass method as a parameter.
5. You don't want to write lot of polymorphic code like in LINQ , you can provide lot of implementation to the Select method.

Hope my explanation could helpful for you.

Best Regards,
Jack

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Answer 2

MSDN docs are generally the best reference
Delegates are well explained with examples : Using Delegates (C# Programming Guide)

Answer 3

Sometimes the best way to learn is to have real-world examples. I've put some together found in the following project.

For example, using an action delegate for assigning custom events for a TaskDialog

Example to report progress and immediately notification of a runtime error

public static void InvokeError()  
{  
    try  
    {  
        for (int index = 0; index < 20; index++)  
        {  
            Progress?.Invoke(index);  
            if (index == 12)  
            {  
                throw new Exception("Intentional error");  
            }  
        }  
    }  
    catch (Exception exception)  
    {  
        ErrorHandler?.Invoke(exception);  
    }  
}  

And the typical samples

public class ActionClass  
{  
    public void InvokeLater(Action action)  
    {  
        action();  
    }  
    public void DoSomethingElse(int param1, string param2)  
    {  
        Debug.WriteLine($"Called in {nameof(DoSomethingElse)} Parameter1: {param1}\tParameter2 {param2}");  
    }  
    public void DoSomething(int parameter1, string parameter2)  
    {  
        Debug.WriteLine($"Called in {nameof(DoSomething)} Parameter1: {parameter1}\tParameter2 {parameter2}");  
    }  
  
    public delegate void SayAnything();  
    public readonly SayHello HelloFunction = () => Debug.WriteLine("Hello!");  
    public static readonly SayAnything HelloFunction2 = () => Debug.WriteLine("Hello!");  
    public static readonly SayAnything GoodbyeFunction2 = () => Debug.WriteLine("Goodbye!");  
    public static readonly Func<string, string, int> SumCharacters = (value1, value2) => value1.Length + value2.Length;  
    public delegate void SayHello();  
    public static readonly Action<string> GreetingsAction = (name) => Debug.WriteLine($"Hello {name}");  
}