Introduction
Delegate is a very powerful feature available in the .NET Framework. In this article, we will explore delegate & its new features which are being introduced in the framework. I will be using Visual Studio 2013 for coding sample code, assuming that you do have basic knowledge of .NET C# code.
I will be explaining the following flavors in this articles:
FuncActionPredicateConverterComparison
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shettyashwin@outlook.com. If you like this article, please don't forget to rate it.
Background
As part of the Interview panel, I have been asked to interview a lot of candidates for the opening we had. At the time of interview when questions were asked on delegates & its features, very few candidates were able to answer this question. Even one of my team members was surprised when I optimized his code & started using action delegate. Hence, I decided to write this article which shares some details on delegates & some of its features.
What are Delegates?
If I can put it into simple words, Delegate is a pointer to a method. Delegate can be passed as a parameter to a method. We can change the method implementation dynamically at run-time, only thing we need to follow doing so would be to maintain the parameter type & return type.
For example: If I declare delegate with return type int & two parameters as string and int respectively, all the references which are set using this delegate should follow this signature.
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internal class Program
{
protected delegate int tempFunctionPointer(string strParameter, int intParamater);
public static void Main()
{
DelegateSample tempObj = new DelegateSample();
tempFunctionPointer funcPointer = tempObj.FirstTestFunction;
funcPointer("hello", 1);
Console.ReadKey();
funcPointer = tempObj.SecondTestFunction;
funcPointer("hello", 1);
Console.ReadKey();
}
}
public class Employee
{
public string Name { get; set; }
public int Age { get; set; }
}
public class XEmployee
{
public string Name { get; set; }
public int Age { get; set; }
public bool IsExEmployee {
get { return true; }
}
}
public class DelegateSample
{
public int FirstTestFunction(string strParameter, int intParamater)
{
Console.WriteLine("First Test Function Execution");
Console.WriteLine(strParameter);
return intParamater;
}
public int SecondTestFunction(string strParameter, int intParamater)
{
Console.WriteLine("Second Test Function Execution");
Console.WriteLine(strParameter);
return intParamater;
}
public void ThirdTestFunction(string strParameter, int intParamater)
{
Console.WriteLine("Third Test Function Execution");
Console.WriteLine(strParameter);
}
public bool FourthTestFunction(Employee employee)
{
return employee.Age < 27;
}
public XEmployee FifthTestFunction(Employee employee)
{
return new XEmployee() {Name = employee.Name, Age = employee.Age};
}
public int SixTestFunction(Employee strParameter1, Employee strParamater2)
{
return strParameter1.Name.CompareTo(strParamater2.Name);
}
}
Delegates can be executed synchronous or asynchronously. Code sample mentioned above is an example of synchronous processing. To make it an Asynchronous process, we need to use BeginInvoke method.
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funcPointer.BeginInvoke("Hello", 1, null, null);
First two parameters are the inputs for the function. 3
rd parameter can be set for getting call back after execution of process. Detailed explanation of making Asynchronous call is available
here.
When Do I Use Delegate?
Looking at the sample above, a lot of us might think this can be also achieved using Interface or abstract class, then why do we need delegate.
Delegate can be used in the following scenarios:
- If you don’t want to pass your interface or abstract class dependence to internal class or layers.
- If the code doesn't need access to any other attributes or method of the class from which logic needs to be processed.
- Event driven implementation needs to be done.
Different Flavors of Delegate
As .NET Framework evolved over a period of time, new flavors have been added to keep implementation simple & optimized. By default, you get all the features & functionality with flavors which you get with delegate. Let’s have a look at Func delegate.
Func<TParameter, TOutput>
Func is logically similar to base delegate implementation. The difference is in the way we declare. At the time of declaration, we need to provide the signature parameter & its return type.
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Func<string, int, int> tempFuncPointer;
First two parameters are the method input parameters. 3rd parameter (always the last parameter) is the out parameter which should be the output return type of the method.
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Func<string, int, int> tempFuncPointer = tempObj.FirstTestFunction;
int value = tempFuncPointer("hello", 3);
Console.ReadKey();
Func is always used when you have return object or type from method. If you have void method, you should be using Action.
Action<TParameter>
Action is used when we do not have any return type from method. Method with void signature is being used with Action delegate.
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Action<string, int> tempActionPointer;
Similar to Func delegate, the first two parameters are the method input parameters. Since we do not have return object or type, all the parameters are considered as input parameters.
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Action<string, int> tempActionPointer = tempObj.ThirdTestFunction;
tempActionPointer("hello", 4);
Console.ReadKey();
Predicate<in T>
Predicate is a function pointer for method which returns boolean value. They are commonly used for iterating a collection or to verify if the value does already exist. Declaration for the same looks like this:
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Predicate<Employee> tempPredicatePointer;
For sample, I have created an Array which holds a list of Employees. Predicate is used to get employee below age of 27:
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Predicate<Employee> tempPredicatePointer = tempObj.FourthTestFunction;
Employee[] lstEmployee = (new Employee[]
{
new Employee(){ Name = "Ashwin", Age = 31},
new Employee(){ Name = "Akil", Age = 25},
new Employee(){ Name = "Amit", Age = 28},
new Employee(){ Name = "Ajay", Age = 29},
});
Employee tempEmployee = Array.Find(lstEmployee, tempPredicatePointer);
Console.WriteLine("Person below 27 age :" + tempEmployee.Name);
Console.ReadKey();
<pre lang="cs">public bool FourthTestFunction(Employee employee)
{
return employee.Age < 27;
}
Converter<TInput, TOutput>
Convertor delegate is used when you need to migrate / convert one collection into another by using some algorithm. Object A gets converted into Object B.
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Converter<Employee, XEmployee> tempConvertorPointer
= new Converter<Employee, XEmployee>(tempObj.FifthTestFunction);
For sample, I have created XEmployee entity. All the Employees in the collection get migrated to XEmployee Entity.
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Employee[] lstEmployee = (new Employee[]
{
new Employee(){ Name = "Ashwin", Age = 31},
new Employee(){ Name = "Akil", Age = 25},
new Employee(){ Name = "Amit", Age = 28},
new Employee(){ Name = "Ajay", Age = 29},
});
Converter<Employee, XEmployee> tempConvertorPointer
= new Converter<Employee, XEmployee>(tempObj.FifthTestFunction);
XEmployee[] xEmployee = Array.ConvertAll(lstEmployee, tempConvertorPointer);
Console.ReadKey();
public XEmployee FifthTestFunction(Employee employee)
{
return new XEmployee() {Name = employee.Name, Age = employee.Age};
}
Comparison<T>
Comparison delegate is used to sort or order the data inside a collection. It takes two parameters as generic input type and return type should always be int. This is how we can declare Comparison delegate.
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Comparison<string> tempComparison = new Comparison<string>(tempObj.SixTestFunction);
In this sample, Employee Name is used to Sort the order. All the entity inside the collection will be processed using SixthTestFunction which contains the logic for processing / sorting the data as per our requirement.
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Comparison<Employee> tempComparisonPointer
= new Comparison<Employee>(tempObj.SixTestFunction);
Array.Sort(lstEmployee, tempComparisonPointer);
Console.ReadKey();
public int SixTestFunction(Employee strParameter1, Employee strParamater2)
{
return strParameter1.Name.CompareTo(strParamater2.Name);
}
Points of Interest
Using the new delegates, we can achieve better level of abstraction & performance can also been gained by avoiding unnecessary iteration or conversion logic. All three delegates (Predicate, Converter, Comparison) do have optimized internal logic for iteration.
References
