Category: C#

Delegate acts as a function pointer.

We define the function to which the delegate can point to in this manner

// Delegate which will point to a method which has no parameter and returns nothing

public delegate void MySimpleDelegate();

// Delegate which will point to a method which takes string as parameter and returns string as well

public delegate string MyComplexDelegate(string message);

Now comes our two function to which delegates would be pointing 

public void SimpleDelegate(){

MessageBox.Show(“My Simple Delegate”);

}  

public string ComplexDelegate(string name){

MessageBox.Show(name);

return “Hi “ + name;

} 

// We have created an instance of our MySimpleDelegate

// which would be referencing SimpleDelegate function

MySimpleDelegate myD = SimpleDelegate;

// when we call the delegate it calls the method which it is pointing to

myD();

// Same thing with our MyComplexDelegate

MyComplexDelegate myAD = AnotherDelegate;

myAD(“Hello”);

// If we know that our function SimpleDelegate() and ComplexDelegate(string name)

// wouldn’t be called by any other code other than the delegate itself we can

// make use of anonymous method i.e. method with no name

// Here again we have done the same thing but used anonymous method

// because we aren’t going to use it anywhere else

MySimpleDelegate myD = delegate

{

MessageBox.Show(“Simple Delegate”);

};

myD();

MyComplexDelegate myAD = delegate(String name)

{

MessageBox.Show(name);

return “Hi “ + name;

};

myAD(“Hello”);

// Now let’s shorten our code further using lambda expression

// () -> no input parameter

// => -> lambda operator

// MessageBox.Show(“Simple delegate”) -> statement block

MySimpleDelegate myD = () => MessageBox.Show(“Simple delegate”);

myD();

//(String name) -> explicitly typed parameter

MyComplexDelegate myAD = (String name) => { MessageBox.Show(name); return name; };

myAD(“Hello”);

Bye.

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Hi,

There are times when we are creating a custom class and the class needs to have it’s own application specific exception which can be thrown so that calling program can be aware of the error condition.

Say we have a class named BillingUpdate which has a condition that the billing amount should never be less than 10,000.

Say it has a function which accepts billing amount in one of it’s methods as a parameter and we need to make the user of this function aware of the condition that it can’t take billing amount less than 10000.

In this case what we can do is

create a custom class BillingException which inherits SystemException class

// creating a custom class that inherits from SystemException.
class BillingException :SystemException
{
// overloading the constructor for passing the message associated with the exception
public BillingException(string message)
: base(message)
{
}
}

Now to use this exception class we can do the following

public void GetBillingAmount(decimal billingAmount)
{
if(billingAmount < 10000M)
{
throw new BillingException(“Billing amount can’t be less than 10000”);
}
}

And the calling code can do something like this

BillingUpdate billingUpdate = new BillingUpdate();
try
{
billingUpdate.GetBillingAmount(9000M);
}
catch(BillingException ex)
{
MessageBox.Show(ex.Message);
}

Bye