One of the constructs many junior programmers struggle with is the delegate. Coming from a world of Visual Basic or Java, many have never seen a function pointer (as a C programmer would every day), so the concept of referencing a function or method in a variable is completely foreign to them. In the early days of C#, delegates had to be instantiated with named methods and were somewhat cumbersome. Today, anonymous delegates and lambda expressions are profuse in many popular frameworks and APIs, so it's important to take a bit of time to cement these concepts into our brains. To help some VB6 programmers adapt to C# and the many equivalent flavors of delegates, I walked through some simple samples to show them the different flavors of delegates. Below is a complete sample showing a few different ways to declare delegates in C#.
using System; using System.Collections.Generic; using System.Linq;
namespace DelegateExample { class Program { public delegate string ProcessStringDelegate(string data);
public static string ReverseStringStaticMethod(string data)
{
return new String(data.Reverse().ToArray());
}
static void Main(string\[\] args)
{
var stringDelegates = new List<ProcessStringDelegate>
{
//==========================================================
// Declare a new delegate instance and pass the name of the method in
new ProcessStringDelegate(ReverseStringStaticMethod),
//==========================================================
// A shortcut is to just and pass the name of the method in
ReverseStringStaticMethod,
//==========================================================
// You can create an anonymous delegate also
delegate (string inputString) //Scramble
{
var outString = inputString;
if (!string.IsNullOrWhiteSpace(inputString))
{
var rand = new Random();
var chs = inputString.ToCharArray();
for (int i = 0; i < inputString.Length \* 3; i++)
{
int x = rand.Next(chs.Length), y = rand.Next(chs.Length);
char c = chs\[x\];
chs\[x\] = chs\[y\];
chs\[y\] = c;
}
outString = new string(chs);
}
return outString;
},
//==========================================================
// yet another syntax would be the lambda expression syntax
inputString => { // ROT13
var array = inputString.ToCharArray();
for (int i = 0; i < array.Length; i++)
{
int n = (int)array\[i\];
n += (n >= 'a' && n <= 'z') ?
((n > 'm') ? 13 : -13) :
((n >= 'A' && n <= 'Z') ?
((n > 'M') ? 13 : -13) : 0);
array\[i\] = (char)n;
}
return new string(array);
}
//==========================================================
};
// Display the results of the delegate calls
var stringToTransform = "Welcome to the jungle!";
System.Console.ForegroundColor = ConsoleColor.Cyan;
System.Console.Write("String to Process: ");
System.Console.ForegroundColor = ConsoleColor.Yellow;
System.Console.WriteLine(stringToTransform);
stringDelegates.ForEach(delegatePointer =>
{
System.Console.WriteLine();
System.Console.ForegroundColor = ConsoleColor.Cyan;
System.Console.Write("Delegate Method Name: ");
System.Console.ForegroundColor = ConsoleColor.Magenta;
System.Console.WriteLine(delegatePointer.Method.Name);
System.Console.ForegroundColor = ConsoleColor.Cyan;
System.Console.Write("Delegate Result: ");
System.Console.ForegroundColor = ConsoleColor.White;
System.Console.WriteLine(delegatePointer(stringToTransform));
});
System.Console.ReadKey();
}
}
}
The output of the program is below:
String to Process: Welcome to the jungle!
Delegate Method Name: ReverseStringStaticMethod Delegate Result: !elgnuj eht ot emocleW
Delegate Method Name: ReverseStringStaticMethod Delegate Result: !elgnuj eht ot emocleW
Delegate Method Name:
b__1 Delegate Result: cg ljotWotem!le une eh
Delegate Method Name:
b__2 Delegate Result: dX_V|`X ?| ?[X ]?{Z_X!