Sunday, February 9, 2014

How to call private method of one class in another class in C#


Sometimes you may want to call the private method declared in one class in another class in c#. Technically it is not possible to access private members of a class outside the class in c#. Either you will need to modify the access specifier of the class member from private to something else.  However if say you are not allowed to change the access specifier of private method but still want to provide a mechanism to enable calling of private method in another class? How can w achieve this in c#? It is very well possible in C# with the help of Delegates. 

Delegates are nothing but pointer to method. If you want to get value of private variable, we can declare a public property similarly if you want to call private method outside the declaring class we can use public property returning delegate (or pointer to the method).

Following construct depicts how delegates can be used to access private method outside a class. Let’s say I have a class A having private method as below –


public class A
    {
        private string ReturnString(string s)
        {
            return "This is returned from private method of class A=" + s;
        }
    } 

Now I want to call the private method “ReturnString” of class A. Declare a delegate above the class A definition as below –
namespace DelegateToAccessPrivateDemo
{
    public delegate string GetPrivateMethodOutput(string);

    public class A
    {
        private string ReturnString(string s)
        {
            return "This is returned from private method of class A=" + s;
        }
    }
}

Now we need to declare a public property inside class A which will return the object of delegate GetPrivateMethodOutput. Therefore class A becomes as shown –
public delegate string GetPrivateMethodOutput(string s); 

    public class A
    {
        private string ReturnString(string s)
        {
            return "This is returned from private method of class A=" + s;
        }

        public GetPrivateMethodOutput MyPrivateMethodOutput
        {
            get
            {
                return new GetPrivateMethodOutput(ReturnString);
            }
        }
    } 

To test the functionality of delegate write following code in Console application’s Program.cs main method –
static void Main(string[] args)
        {
            GetPrivateMethodOutput privateMethod = null;
            A a = new A();
            privateMethod = new GetPrivateMethodOutput(a.MyPrivateMethodOutput);
            Console.WriteLine(privateMethod("!!Learned use of delegate!!"));
            Console.ReadLine();
        } 

The output is as follows –

 

Hope this helps in understanding the advantage of delegate in accessing private method of a class.
Cheers…
Happy Delegating!!

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