Func delegate with no return type

Question

All of the Func delegates return a value. What are the .NET delegates that can be used with methods that return void?

Answer 1

All Func delegates return something; all the Action delegates return void.

Func<TResult> takes no arguments and returns TResult:

public delegate TResult Func<TResult>()

Action<T> takes one argument and does not return a value:

public delegate void Action<T>(T obj)

Action is the simplest, 'bare' delegate:

public delegate void Action()

There's also Func<TArg1, TResult> and Action<TArg1, TArg2> (and others up to 16 arguments). All of these (except for Action<T>) are new to .NET 3.5 (defined in System.Core).

Answer 2

... takes no arguments and has a void return type?

I believe Action is a solution to this.

Answer 3

All of the Func delegates take at least one parameter

That's not true. They all take at least one type argument, but that argument determines the return type.

So Func<T> accepts no parameters and returns a value. Use Action or Action<T> when you don't want to return a value.

Answer 4

Try System.Func<T> and System.Action

Answer 5

A very easy way to invoke return and non return value subroutines. is using Func and Action respectively. (see also https://msdn.microsoft.com/en-us/library/018hxwa8(v=vs.110).aspx)

Try this this example

using System;

public class Program
{
    private Func<string,string> FunctionPTR = null;  
    private Func<string,string, string> FunctionPTR1 = null;  
    private Action<object> ProcedurePTR = null; 



    private string Display(string message)  
    {  
        Console.WriteLine(message);  
        return null;  
    }  

    private string Display(string message1,string message2)  
    {  
        Console.WriteLine(message1);  
        Console.WriteLine(message2);  
        return null;  
    }  

    public void ObjectProcess(object param)
    {
        if (param == null)
        {
            throw new ArgumentNullException("Parameter is null or missing");
        }
        else 
        {
            Console.WriteLine("Object is valid");
        }
    }


    public void Main(string[] args)  
    {  
        FunctionPTR = Display;  
        FunctionPTR1= Display;  
        ProcedurePTR = ObjectProcess;
        FunctionPTR("Welcome to function pointer sample.");  
        FunctionPTR1("Welcome","This is function pointer sample");   
        ProcedurePTR(new object());
    }  
}

Answer 6

Occasionally you will want to write a delegate for event handling, in which case you can take advantage of System.EvenHandler<T> which implicitly accepts an argument of type object in addition to the second parameter that should derive from EventArgs. EventHandlers will return void

I personally found this useful during testing for creating a one-off callback in a function body.

Answer 7

... takes no arguments and has a void return type?

If you are writing for System.Windows.Forms, You can also use:

public delegate void MethodInvoker()