Part 65 - C# Tutorial - Indexers in c# Video Lecture - C sharp Enhance

welcome to prism technologies I am
vented this is part 65 of c-sharp
tutorial in this video we'll discuss
about creating indexers please watch
about 64 before proceeding with this
video in part 64 we discussed about how
and where indexes are used within dotnet
framework
now let's practically understand
creating indexers with an example let's
flip to visual studio here I have an
asp.net web application project let's
add a class file to this project and
let's call it company dot CS now a
company contains employees to
encapsulate employee information let's
add a class employee so public class
employee this class is going to contain
you know three auto implemented
properties employee ID so public end
employee ID it's going to have the
default getting set accessors without
any specific implementation let me add
name and gender properties as well name
is of type string so let's change the
data type to string and the property
name is going to be name and gender is
also going to be string alright so we
have an employee class with three auto
implemented properties now within the
company class usually a company contains
a list of employees too so to hold those
lists of employees I'm going to create a
private variable here of type list
employee and let's call this list
employees and then within the
constructor of this company class I'm
going to initialize this list okay so
usually a constructor will have the same
name as that of the class and doesn't
have a return type so here this is the
company class constructor look at the
name is the same name as stead of the
class and it doesn't have a return type
so I'm going to initialize this list
here so list employees is equal to new
list of employee and then I'm going to
add some employees to this list here so
as soon as
accompanying object then I will have all
the list of employees that belong to
that company within this object here
okay now in reality we may actually load
the list of employees from a database
table but to keep things simple here to
understand indexes and focus on indexers
i'm going to add some employees within
code okay so list employees dot add I'm
going to add a new employee and
obviously we need to specify the
properties so employee ID let's say
that's one name of the employee is going
to be let's say might and his gender is
male all right so at this point we have
an employee added to our list but let's
add a few more employees and to speed
things up I have that already type so
let me copy and paste that here and look
at this bullets very simple it's the
same code we're adding you know
different employees here with different
IDs and names and genders okay so at
this point we have this company class
within that we have this private
variable of type list employee and
within the constructor we are
initializing that object and adding
employees to that list okay so this is
the private list meaning nobody can
access this list outside of this class
okay but then remember in the previous
session we discussed about using sequel
data reader object and a session object
using the indexers in a similar fashion
I want to be able to use this company
class and and retrieve the employees
using employee ID and at the same time
using employee ID indexer I should be
able to change the names of the
employees okay is that possible to
implement an indexer like that for our
class company absolutely let's see how
to do that okay now we create indexes
using this keyword so public so the
return type of this indexer is going to
be string because I give it an employee
ID to this company class I give an
employee ID and it has to return me the
name of the employee you know whom whose
ID matches with that employee ID so it's
going to return the name which is string
and then we create an index in C
using this keyword and then I open the
square bracket and then what is the data
type of employee ID it's an integer so
I'm going to pass an employee ID and the
class should return me the name of the
employee whose ID matches with the past
an employee ID so int employee ID okay
so just like properties you know if you
are familiar with properties
implementing indexes is very straight
forward just like properties it's gonna
have ket and set accessories we
discussed about properties in the
previous session of this video series so
please watch that video so it's gonna
have a get accessor so what should this
get access or do you know for the given
employee ID it should return me the name
of the employee okay so to do that where
are the list of employees present the
list of employees present in this list
okay so what I'm going to do here I'm
going to use little bit of link here you
know to return the employee name whose
ID matches with what is being passed
into this index ax so I'm going to say
return you know we have the list list as
list employees so from this list okay I
want to get a first or default element
so within this list find an employee EMP
such that that employee dot employee ID
should match with whatever we are
passing into this indexer okay so this
method is going to return an employee
object okay look at that first or
default method you know look at the
return type from the intelligence it's
returning an employee object and from
that object I want to pick up their name
and return that so that's the get
accessor of this indexer now what should
the set access or do now if I set an
employee ID you know for example I will
say company of employee company of one
you know something like this the usage
of this indexer should be something like
this if I say let's say I have a company
object and when I say company of three
is equal to you know maybe Jade
that's the name then what should happen
for an employee with ID is equal to
three we should change the name to Jade
okay so that's what the set accessors
should do for the given employee ID
change their name to whatever value they
are going to set so to do that what I'm
going to do from the list first we
should find that employee so lest
employee is first or default you know
the same kind of the expression so for
the given employee find the employee ID
if that matches with what is passed then
then set their name to whatever value
they are passed setting so here we are
setting Jade so Jade will be assigned to
the name of property of the employee so
it's basically employee ID so let's copy
it yeah so Jade will be set as the name
for the given employee ID you know
whatever employee ID you pass in if
there is an employee with that ID you
know we get the employee and their name
is set to that value Jade in this case
okay so we have the indexer implemented
here so the points to note here is we
you we implement the index are using
this keyword and exercise will have a
return type and it it has parameters and
then it has get and set accessors just
like properties okay so we are done
implementing indexer for our company
class so let's build the solution let's
see how to actually use this indexer on
a webform so let's go back to the
code-behind file of this waveform one
and let's print the names of some of the
employees so here we have lists of
around 8 employees so let's say I want
to print out the name of employee 2 5
and 8 okay using indexers and to do that
so response dot right let's say name of
employee with ID is equal to two let's
say
now I'm going to use you know first we
need to create an instance of company
class just like how you know we are we
are using the session object and sequel
data reader object so first let me
create an instance of the company class
company is equal to new company and
remember what happens when we create a
constructor of disk you know when we
when we create an instance of this
company class you know the constructor
gets invoked and within the constructor
we are creating a new list and
populating the list with some employees
here okay
so that's what happens when I create
this company object now I want to
retrieve the name of the employee whose
ID is two and look at this the moment I
opened the square bracket it it detects
that there is an indexer on employee ID
and then the moment I pass to it it look
at the return type its string meaning
it's going to return the name of the
employee that's that and then let's put
an HTML break so that the next employee
will come in a different line all right
so let's copy this and you know let's
say name of the employee with ID is
equal to five name of employee with ID
is equal to eight let's get the employee
named with ID five and eight and then
what I also want to do here we are only
retrieving you know the names of the
employees okay by passing in the IDS
obviously when we pass in the idea and
if we want to the name then this get
access or of this indexer will be
invoked and now let's say I want to
change the names of those employees is
it possible with the indexer absolutely
so let's say response tort right let's
say here changing names of employees
with ID is equal to 2 comma five and
eight
and let's write an HTML break there and
how do we change the employee names
using indexers all you need to do is so
use the company object here so company
object now let's say if I want to change
the name of the employee that ID is
equal to to company of two is equal to
let's say second employee name changed
similarly let's do it four five and
eight as well so five and eight so after
the name is changed let's print their
names once again so it's the same piece
of code so we can just copy and paste it
there alright
so these three lines should print the
name of the employees before change so
if you look at employees to five and
they eat within the company class two is
pam 5s Emily a test ban so that's what
should be the names of the employees you
know before we have changed them and we
are retrieving them using the indexer so
time Emily and Ben and we are changing
and we are saying changing names of
employees with ID is equal to two five
and eight so second employee name
changed oh it should actually be fifth
employee name change I think it's
because of copy/paste error there
so let's actually call this first
employee name changed eighth employee
name changed and let's also have an
additional HTML break there so that
output will be properly formatted so
here look at that the employee names
with two five and eight is Pam Emily
been changing names of employees with ID
is equal to two five and eight and look
at that you know after we have changed
the names second employee name changed
fifth employee name changed and that
should be eight employee name changed I
think we didn't do it for the last
employee so that should be a the
employee anyway so here we are using the
set
I mean set accessor of the indexer to
actually change the values there okay so
if you understand properties
implementing indexes is pretty
straightforward
so the points to remember we use this
keyword to create an index are just like
properties indexes have khet and set
accessors indexes can also be overloaded
we will discuss about overloading
indexers in our next video session and
this is how we have used the get and set
accesses of our company object you know
of that index our employee ID integral
indexer on this slide you can find the
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of interview questions that's it for
today thank you for listening have a
great day