Uses of Action delegate in C# [closed]

Answer 1

Well one thing you could do is if you have a switch:

switch(SomeEnum)
{
  case SomeEnum.One:
      DoThings(someUser);
      break;
  case SomeEnum.Two:
      DoSomethingElse(someUser);
      break;
}

And with the might power of actions you can turn that switch into a dictionary:

Dictionary<SomeEnum, Action<User>> methodList = 
    new Dictionary<SomeEnum, Action<User>>()

methodList.Add(SomeEnum.One, DoSomething);
methodList.Add(SomeEnum.Two, DoSomethingElse); 

...

methodList[SomeEnum](someUser);

Or you could take this farther:

SomeOtherMethod(Action<User> someMethodToUse, User someUser)
{
    someMethodToUse(someUser);
}  

....

var neededMethod = methodList[SomeEnum];
SomeOtherMethod(neededMethod, someUser);

Just a couple of examples. Of course the more obvious use would be Linq extension methods.

Answer 2

MSDN says:

This delegate is used by the Array.ForEach method and the List.ForEach method to perform an action on each element of the array or list.

Except that, you can use it as a generic delegate that takes 1-3 parameters without returning any value.

Answer 3

You can use actions for short event handlers:

btnSubmit.Click += (sender, e) => MessageBox.Show("You clicked save!");

Answer 4

We use a lot of Action delegate functionality in tests. When we need to build some default object and later need to modify it. I made little example. To build default person (John Doe) object we use BuildPerson() function. Later we add Jane Doe too, but we modify her birthdate and name and height.

public class Program
{
        public static void Main(string[] args)
        {
            var person1 = BuildPerson();

            Console.WriteLine(person1.Firstname);
            Console.WriteLine(person1.Lastname);
            Console.WriteLine(person1.BirthDate);
            Console.WriteLine(person1.Height);

            var person2 = BuildPerson(p =>
            {
                p.Firstname = "Jane";
                p.BirthDate = DateTime.Today;
                p.Height = 1.76;
            });

            Console.WriteLine(person2.Firstname);
            Console.WriteLine(person2.Lastname);
            Console.WriteLine(person2.BirthDate);
            Console.WriteLine(person2.Height);

            Console.Read();
        }

        public static Person BuildPerson(Action<Person> overrideAction = null)
        {
            var person = new Person()
            {
                Firstname = "John",
                Lastname = "Doe",
                BirthDate = new DateTime(2012, 2, 2)
            };

            if (overrideAction != null)
                overrideAction(person);

            return person;
        }
    }

    public class Person
    {
        public string Firstname { get; set; }
        public string Lastname { get; set; }
        public DateTime BirthDate { get; set; }
        public double Height { get; set; }
    }

Answer 5

Here is a small example that shows the usefulness of the Action delegate

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Action<String> print = new Action<String>(Program.Print);

        List<String> names = new List<String> { "andrew", "nicole" };

        names.ForEach(print);

        Console.Read();
    }

    static void Print(String s)
    {
        Console.WriteLine(s);
    }
}

Notice that the foreach method iterates the collection of names and executes the print method against each member of the collection. This a bit of a paradigm shift for us C# developers as we move towards a more functional style of programming. (For more info on the computer science behind it read this: http://en.wikipedia.org/wiki/Map_(higher-order_function).

Now if you are using C# 3 you can slick this up a bit with a lambda expression like so:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<String> names = new List<String> { "andrew", "nicole" };

        names.ForEach(s => Console.WriteLine(s));

        Console.Read();
    }
}

Answer 6

I use it when I am dealing with Illegal Cross Thread Calls For example:

DataRow dr = GetRow();
this.Invoke(new Action(() => {
   txtFname.Text = dr["Fname"].ToString();
   txtLname.Text = dr["Lname"].ToString(); 
   txtMI.Text = dr["MI"].ToString();
   txtSSN.Text = dr["SSN"].ToString();
   txtSSN.ButtonsRight["OpenDialog"].Visible = true;
   txtSSN.ButtonsRight["ListSSN"].Visible = true;
   txtSSN.Focus();
}));

I must give credit to Reed Copsey SO user 65358 for the solution. My full question with answers is SO Question 2587930