Saturday, 21 January 2012

Collection initializer in C# 3.0/3.5,Collection in .net,CSharp



Collection initializer in C# 3.0

1. Collection initializer is new feature of C# 3.0
2. Collection initializer gives a simple syntax to create instance of a collection.
3. Any object that is implementing System.Collections.Generic.ICollection<T> can be initialized with collection initializer.
Let us say, we have a class
Student.cs




public  class Student
    {
       public string FirstName { get; set; }
       public string LastName { get; set; }
    }
Now if we want to make collection of this class and add items of type student in that collection and retrieve through the collection, we need to write below code
Program.cs




using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication16
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Student> lstStudent = new List<Student>();
            Student std = new Student();
            std.FirstName = "Dhananjay";
            std.LastName = "Kumar ";
            lstStudent.Add(std);
            std = new Student();
            std.FirstName = "Mritunjay ";
            std.LastName = "Kumar";
            lstStudent.Add(std);
            foreach (Student resstd in lstStudent)
            {
                Console.WriteLine(resstd.FirstName);
            }
            Console.Read();
        }
    }
Output
clip_image002
In above code,
1. An instance of List of Student is getting created.
2. An instance of the Student is getting created.
3. Using the Add method on the list, instance of being added to list of students.
4. Using For each statement iterating through the list to get the values. Now, if instance of Student class can be assigned to List of student at the time of creation of instance of list then we call it automatic collection initializer.
clip_image004
If we see the above syntax
1. It is highly readable.
2. It is single statement.
3. Instance of Student class is getting added on the fly. And we can retrieve the values as below,
clip_image005
In retrieving implicit type local variable is being used to fetch the different instance of the student in list of student
Program.cs


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication16
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Student> lstStudent = new List<Student>()
                                         {
                                             new Student{FirstName ="Dhananjay" ,LastName="Kumar"},
                                             new Student {FirstName ="Mritunjay", LastName ="Kumar"}
                                         };
            foreach (var r in lstStudent)
            {
                Console.WriteLine(r.FirstName);
            }
            Console.Read();
        }
    }
Output
clip_image007

How it internally works?
A collection initializer invokes the ICollection<T>.Add(T) method for each specified element in order. In the above example , it will call
ICollection<Student>.Add(instance of Student )
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