.NET Framework missing from Visual Studio 2010 new project dialog box


To resolve this issue, download and install .NET Framework 3.5 sp1.

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=ab99342f-5d1a-413d-8319-81da479ab0d7&displaylang=en

Or if it is Windows Server 2008 R2,  just enable the .NET Framework 3.5.1 Features using Server Manager or else you will get the following error

“You must use role management tool to install or configure Microsoft .NET Framework 3.5”

Bye.

Understanding Constructors (C#)


What is constructor?

Constructor is a special type of function member of a class. It is used to initialize the instance variables of the object.

Person myPerson=new Person();

Here the new operator is used to allocate the memory needed to store the data of the object.

Now suppose this is how we have defined our Person class.

  public class Person
        {
            public string FirstName { get; set; }
            public string LastName { get; set; }
        }  
   

( here we have used Automatic Properties feature of C# 3.0 to declare our properties FirstName and LastName)

Here in our class we haven’t defined a constructor but we are still able to create instance variables of the Person Object using following line of code

Person p = new Person();
 

The reason it is possible is because we don’t have to explicitly declare constructor for a class, C# automatically provides a default parameterless constructor for that class. The default constructor will initialize any fields of the class to their zero-equivalent values.

We can also write our own constructors, the things to remember are

  • They don’t have a return type.
  • Their name should be same as the name of the class.
  • Should contain a parameter list, which could be left empty.

Now the question is why would we be writing our own constructors?

Well the reason is because constructors can be used to pass initial values for an object’s fields at the time when an object is being instantiated.

For our above Person class

instead of the following code 

    Person p = new Person();
    p.FirstName = "Nishant";
    p.LastName = "Rana";

 

we can do the same in single line of code

Person p = new Person("Nishant", "Rana");
 

The constructor would be defined in the following manner

 public Person(string fname, string lname)
          {
              FirstName = fname;
              LastName = lname;
          }

One thing we have to remember is that if we are defining our own Parameterized constructor the default constructor would be eliminated.

We won’t be able to create person class object using default constructor.

i.e. Person p=new Person(); // it won’t compile.

In this case then we need to explicitly write a default constructor.

public Person()
        { 

        }

bye..

Events in C#


We’ll take a simple and useful scenario to make our understanding of Events as clear as possible.
First of all copy and paste the code below. We’ll try understanding the code than.

using System;
public class ResultDeclarationEventArgs : EventArgs
{
private string message;
public ResultDeclarationEventArgs(string message)
{
this.message = message;
}
public string Messsage
{
get
{
return message;
}
}
}
public delegate void ResultHandler(object sender, ResultDeclarationEventArgs e);
public class Kid
{
private int percentage;
public event ResultHandler onResultDeclaration;
public int Percentage
{
set
{
percentage = value;
if(percentage > 80)
{
ResultDeclarationEventArgs myREA = new ResultDeclarationEventArgs( ” I got Distinction”);
onResultDeclaration(this, myREA);
}
if(percentage > 60 && percentage < 80)
{
ResultDeclarationEventArgs myREA = new ResultDeclarationEventArgs(” I got FirstClass”);
onResultDeclaration(this, myREA);
}
if(percentage > 40 && percentage < 60)
{
ResultDeclarationEventArgs myREA = new ResultDeclarationEventArgs(” I got SecondClass”);
onResultDeclaration(this, myREA);
}
if(percentage < 40)
{
ResultDeclarationEventArgs myREA = new ResultDeclarationEventArgs(” Sorry I failed “);
onResultDeclaration(this, myREA);
}
}
}
}
public class Mom
{
public Mom(Kid myKid)
{
myKid.onResultDeclaration += new ResultHandler(GiveMsgToMom);
}
void GiveMsgToMom(object sender, ResultDeclarationEventArgs e)
{
Console.WriteLine(e.Messsage);
}
}

public class Dad
{
public Dad(Kid myKid)
{
myKid.onResultDeclaration += new ResultHandler(GiveMsgToDad);
}
void GiveMsgToDad(object sender, ResultDeclarationEventArgs e)
{
Console.WriteLine(e.Messsage);
}
}

class myDemo
{
public static void Main()
{
Kid kid = new Kid();
Mom mom = new Mom(kid);
Dad dad = new Dad(kid);
Console.WriteLine(“Please enter the percentage of the Kid”);
string percentage = Console.ReadLine();
kid.Percentage = Convert.ToInt32(percentage);
}
}

The scenario is something like this First there is a class named Kid. It has a field called Percentage and declares an event OnResultDeclaration. It is of type ResultHandler. ResultHandler is a delegate. public delegate void ResultHandler(object sender, ResultDeclarationEventArgs e);
It can point or refer to any method which has return type void and takes as parameter an object and ResultDeclarationEventArgs.
Object will give the name of the sender who has called this eventhandler and ResultDeclarationEventArgs is to pass any information regarding the event.

ResultDeclarationEventArgs is a class that derives from EventArgs class. It has a message field which will contain the message the Kid class, which has the event OnResultDeclaration, would like to convey to the class (e.g. Mom, Dad) which are interested in that event.
For this reason, we have our event handlers(method) inside Mom and Dad class which have the same signature as defined by the event.
void GiveMsgToMom(object sender, ResultDeclarationEventArgs e)
void GiveMsgToDad(object sender, ResultDeclarationEventArgs e)
Than we register these eventHandler to the events.
myKid.onResultDeclaration += new ResultHandler(GiveMsgToDad);
myKid.onResultDeclaration += new ResultHandler(GiveMsgToDad);

Kid class will check for the percentage passed in and accordingly set’s the message.
Whatever message is set is than displayed in the Event handler inside Mom and Dad class using e.Message

Understading Delegates


What are delegates?
Delegates are object that refer to an method. Normally we refer to objects, however referring to an object isn’t any different from referring a method they too have physical location in memory.

Why use delegate?
One delegate can be used to call different methods during runtime of a program by simply changing the method to which the delegate refers.
and Delegates Support Events.

delegate ret-type name(paramerter-list);
e.g. delegate string MyDelegate();

The MyDelegate can call any method whose return type is string and accepts no parameter. It can be instance method or a static method.

delegate string MyDelegate(String s);
class Program
{
static string GetNameLower(String s)
{
return s.ToLower() ;
}
static string GetNameUpper(string s)
{
return s.ToUpper();
}
static void Main(string[] args)
{
MyDelegate myD = new MyDelegate(GetNameLower); //or myD=GetNameLower
string s1 = myD(“Hi Nishant”);
Console.WriteLine(s1);
myD = new MyDelegate(GetNameUpper); //or myD=GetNameUpper
string s2 = myD(“Hi Nishant”);
Console.WriteLine(s2);
}
}

Understanding Multicasting

We can have chain of methods that will be called automatically when a delegate is invoked.
For this we will use += operator to add methods to chain and -= to remvove a method.
If delegate returns value than value returned by the last method becomes the return value of entire deleagation invocation. Thus a delegate making use of multicasting will have void as return type.

delegate void MyDelegate();
class Program
{
static void GetNameLower()
{
Console.WriteLine(“GetNameLower Called”);
}
static void GetNameUpper()
{
Console.WriteLine(“GetNameUpper Called”);
}
static void Main(string[] args)
{
MyDelegate myD = GetNameLower;
myD +=GetNameUpper;
myD(); //invoking the delegate
}

Understanding Static keyword in C#


Static keyword can be applied to
Class, field, method, properties, operator, event and constructors.
Static member belongs to the class and not to any object of the class.
They can be used without creating the instance of the class.

For e.g. Static Void Main()
It is called by the operating system on program execution
To access the static member we’ll use

ClassName.staticmember

When a variable is declared as static internally what happens is that all the instances of the class share the same static variable. A static variable is initialized when its class is loaded. If not
initialized explicitly then
it is initialized to zero for numeric variable
null in case of object references
false for boolean

StaticMethod they can only contain static member and call other static method.
If we need to access them than it can be done through the object of that class

class Game
{
string getGameName()
{
……………….
}
public static void getNameThroughStatic(Game g)
{
g.getGameName(); // accessing static method
}
}

When to use them?
Well we can use them when we need to maintain information applicable to the entire class

suppose we have a class Employees there we can have a static count variable to keep track of no of employees.

class Employees
{
static in count=0;
public Employees()
{
count++;
}

~Employees
{
count–;
}

}

What are Static Constructor?
They can be used to initialize the static variables.
They are called automatically and before the instance constructor (if called any).

for above class
static Employees() // no other access modifiers for them
{}

What are static Classes?
A class whose objects can’t be created and which can only have static members. They can’t be inherited as well.
They can have static constructor

Why use static Classes?
It can be used to group related static method.

Internal Access Modifier in C#


In C#
The internal access modifier can be applied to
Classes and it’s member
Structure and it’s member
Enumeration
Interface

This way it is available to all the files within that assembly.
Particularly useful when creating software components.

It can be used in conjunction with protected to produce
protected internal access modifier
It can be applied only to
Class members

It is available withing it’s own assembly or to derived types.

For e.g.

Say if we create an Class Library which has a class like

namespace ClassLibrary1
{
public class MyClass

……

And then you create

Now we create new project say a windows application and add a refrence to that dll
And can create the object of that class lik

MyClass my=new MyClass();

this works fine,

now if we modify the definition of the class by replacing public with internal and update the assembly

namespace ClassLibrary1{
internal class MyClass

This time if we try to create the object of MyClass which is inside our referenced assembly
The error which we will get is

MyClass is inaccessible due to its protection level.

That’s why they are basically used in component development so that any other class couldn’t be able to access it i.e. create objects of it.

That’s it

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