Delegates, Why? [duplicate]

Answer 1

It seems many of the answers have to do with inline delegates, which in my opinion are easier to make sense of than what I'll call "classic delegates."

Below is my example of how delegates allow a consuming class to change or augment behaviour (by effectively adding "hooks" so a consumer can do things before or after a critical action and/or prevent that behaviour altogether). Notice that all of the decision-making logic is provided from outside the StringSaver class. Now consider that there may be 4 different consumers of this class -- each of them can implement their own Verification and Notification logic, or none, as appropriate.

internal class StringSaver
{
    public void Save()
    {
        if(BeforeSave != null)
        {
            var shouldProceed = BeforeSave(thingsToSave);
            if(!shouldProceed) return;
        }
        BeforeSave(thingsToSave);

        // do the save

        if (AfterSave != null) AfterSave();
    }

    IList thingsToSave;
    public void Add(string thing) { thingsToSave.Add(thing); }

    public Verification BeforeSave;
    public Notification AfterSave;
}

public delegate bool Verification(IEnumerable thingsBeingSaved);
public delegate void Notification();

public class SomeUtility
{
    public void SaveSomeStrings(params string[] strings)
    {
        var saver = new StringSaver
            {
                BeforeSave = ValidateStrings, 
                AfterSave = ReportSuccess
            };

        foreach (var s in strings) saver.Add(s);

        saver.Save();
    }

    bool ValidateStrings(IEnumerable strings)
    {
        return !strings.Any(s => s.Contains("RESTRICTED"));
    }

    void ReportSuccess()
    {
        Console.WriteLine("Saved successfully");
    }
}

I guess the point is that the method to which the delegate points is not necessarily in the class exposing the delegate member.