C# Indexers:
C# indexers are like properties. It allows to access instances like an array with an index.
It always represents collection objects but exposes arguments using which we can use to identify a particular element in the collection at a time.
We can access an indexer by indexing the class instance with the appropriate index parameter.
We can overload indexers with different data types and create multiple indexers for a class to expose & access different collections using the same class instance.
It acts as a member of a class but is used to access a data item of a collection from outside the class.
When do we use it?
Let’s say we have to load a collection object in memory and we don’t know upfront exactly how much memory it would take. Indexers help to set up an approach to load a small chunk of the entire data load, process it, and then move on to the next chunk.
It helps to abstract collection type in the model from the usage class as it always allows to access one data item at a time. This helps code easier to understand and maintain.
Indexer should be used if providing an index to an object makes sense.
Simple Example:
public class Employee
{
public string Name{get;set;}
public int Id {get;set;}
public string Department{get;set;}
public int DepartmentId{get;set;}
public string City{get;set;}
public string Zip{get;set;}
}
public enum DepartmentEnum{
None = 0,
Engineering,
Accounting,
Economics,
Politics
}
internal class Program
{
private static void Main(string[] args)
{
Console.WriteLine(“Hello, World!”);
var processor = new EmployeeProcessor(DepartmentEnum.Engineering);
processor.ProcessPayroll();
processor.ProcessHealthInsurance();
Console.WriteLine($”Total engineering employees – {processor[DepartmentEnum.Engineering].Count()}“);
Console.ReadKey();
}
}
public class EmployeeProcessor
{
private List<Employee> employees = new List<Employee>();
public EmployeeProcessor(DepartmentEnum department)
{
LoadEmployeesByDepartment(department);
}
public List<Employee> this[DepartmentEnum department]
{
get
{
return employees.Where(x=> x.DepartmentId == (int)department).ToList();
}
}
private void LoadEmployeesByDepartment(DepartmentEnum department)
{
//load it from the data source. I am Hard coding for a blog
if(department == DepartmentEnum.Engineering)
{
employees.Add(
new Employee()
{
Name = “Nirmal kumar”,
Id = 1,
Department = “Engineering”,
DepartmentId = 1,
City = “Raleigh”,
Zip = “27616”
});
}
else if(department == DepartmentEnum.Accounting)
{
employees.Add(new Employee()
{
Name = “Preethi”,
Id = 1,
Department = “Accounting”,
DepartmentId = 2,
City = “Atlanta”,
Zip = “12345”
});
}
else if(department == DepartmentEnum.Economics)
{
employees.Add(new Employee()
{
Name = “Adithi”,
Id = 1,
Department = “Economics”,
DepartmentId = 3,
City = “New york”,
Zip = “23456”
});
employees.Add(new Employee()
{
Name = “Pranavi”,
Id = 2,
Department = “Economics”,
DepartmentId = 3,
City = “New york”,
Zip = “23456”
});
}
}
public void ProcessPayroll(){}
public void ProcessHealthInsurance(){}
}
