Part 50 C# Tutorial Internal and Protected Internal Access Modifiers

hello welcome to prism technologies I am
venket this is part 50 access modifiers
in this session we'll talk about
internal and protected internal access
modifiers in the previous session we
learned about private public and
protected access modifiers and we know
that a private member is accessible only
within the containing class whereas a
public member is accessible anywhere
there are no restrictions whatsoever and
a protected member is available with the
containing type and the types derived
from the containing time okay in this
session we'll talk about internal access
modifier and protected internal okay a
member with internal access modifier is
basically available anywhere within the
containing assembly so to understand
internal access we need to understand
the concept of assemblies now in.net if
you compile a project an assembly is
generated and end ordinate basically the
assemblies are of two types executables
and dll's okay usually a console
application generates in dot exe Windows
application generates dot exe but
whereas a web application a class
library generates in dot DLL okay now if
you look at this solution it has got a
console application so then we build the
solution a DLL for this project will be
generated now in this solution we only
have one project
so obviously one executable or one
assembly will be generated since this is
a console application and executable
will be generated and if you want to
look at that physical assembly what you
need to do is just right click on that
open folder when in in Windows Explorer
bin directory debug and you see that we
have introduction to c-sharp that's the
same name as that of your project ok so
this assembly gets the name of its
project and since it's a control
application it will generate an exe and
not a DLL ok so this is your assembly so
what what does this assembly contains it
contains the intermediate language of
you
project source code so all your project
classes methods structures etc will be
compiled intermediate language is
generated and it is packaged into this
assembly which we have just seen alright
now since we want to understand internal
axis modifier here we need to have you
know different assemblies so that you
know we can define an internal member in
one of the assemblies try to access that
from a different assembly and see if
it's X is alone on ok and to do that we
need to add more projects to this
solution so to add it to add another
project to the solution just right click
on the solution add new project and we
shall see sharp as a programming
language I'm gonna select class library
the project type and let's call this
assembly one so I'm giving my project
assembly one as the name of my project
click OK
so what is this going to do it's going
to generate another project so if you
look at the solution flyer file here you
have two projects in the solution 1
class library 1 console application
let's add another class library and to
do that add new project I'm gonna call
this assembly too so assembly 2 and when
I click ok so another project has had
now if I build a solution basically all
these three projects will be compiled
and for each project and assembly will
be generated so if I want to find the
assembly of this project just right
click on that project open folder and
Windows Explorer get into the bin
directory go into the debug directory
and you see that there is a dll this
time okay so in dotnet assemblies are of
two types dot dll or not exe now since
we have understood the concept of
assemblies here okay now if you look at
this assembly one we have a file a class
file class 1 dot CS let's leave that
name but in reality we give it a
meaningful name ok for example if I'm
creating a customer class I will name it
after the class maybe custom
CS similarly if I'm creating an employee
class employee CS since this is just a
simple example I'm gonna leave that as
class one CS so class 1 dot CS let's get
rid of this unwanted using directories
here let's make it the program as simple
as possible okay so if you look at that
we have namespace 1 I'm gonna call this
assembly one last one so this is class
one that is present in this assembly and
in this class I'm going to create a an
internal member so until now oops not
interface in there now interior and
let's call it ID and let's initialize
that to maybe once you want so we have
this internal member here now if it was
public then it's accessible anywhere
there are no restrictions since this is
internal okay it's available only to the
classes that are present within this
assembly so if you add another class
look at this to this project you can add
another class if you want ok and even to
that class this member will be available
ok or what I can do in the same file I
can create another class maybe public
class maybe let's call that as assembly
1 class 2
and now within this class let's say I
have a matter public void sample method
and if I create you know an instance of
this class here I should be able to
access this member so assembly one class
maybe a one is equal to new assembly
class one
and when I say a1 dot I'm able to access
that ID member so if I simply say
console.readline
he just writes that onto the console and
now when we build this go to the build
menu build solution we have an error
here somewhere what does it say the
namespace assembly 1 already contains a
definition for assembly 1 class 1 okay
let's call this class 2 because we
already have class 1 here
okay so what we are doing here assembly
class a1 is equal to you assembly class
one we created an instance and we are
trying to access the ID property so if I
build this solution it should build
without any problem okay since this is
an internal remember I can access this
within any class of this assembly one
but on the other hand if I try to access
this look at this I have another project
and I built this assembly to project we
get another assembly
so from this assembly if I try to access
this internal member just like how we
have done here we will get a compiler
error okay so let's try to do that and
see what happens so in class one so this
belongs to assembly to project so let's
say let's call this class s assembly to
class one so that we are clear on what
class we are creating so we have another
class in assembly two now for this class
let's get rid of this unwanted code
first okay so if you look at this this
class is present in this assembly to
project now what we want to do we want
to create an instance of this class and
then access the ID property in this
assembly but we know that the ID
property is internal which means this
this it's not property it's a feel so
this field is only accessible within the
containing assembly within this assembly
but we are trying to access it from
another assembly and internal access
modifier will not allow us to do that
okay so let's see that and before we do
that if we try to create an instance of
this class look at this within the same
assembly and trying to create an
instance of this class here and it works
fine but on the other hand if I try to
create an instance of this class here or
let's say public void maybe we'll call
this print method and then this one I am
trying to you know look at that a 1 is
equal to new
basically you can see a red squiggly
there which is indicating you know I
don't know about this type so if I hover
my mouse look at that the type of
namespace assembly 1 class 1 couldn't be
found
are you missing a using directory are in
assembly reference and that error
message is very meaningful so are you
missing a using directory here here are
and assembly reference ok now where is
this class present this class is present
in assembly one project and and we know
that when we build this project assembly
one door dll is generated now we need to
use the dll in this project in order to
be able to access this class ok just
like how you're using console class look
at this for example if I want to use the
console class against a console class
but where is this control class coming
from it's coming from the system
namespace now if you look at the
references you have the system assembly
here and within that system assembly we
have the console class that's how that's
why you are able to access that but on
the other hand assembly one class is
available in this assembly one project
or in this assembly one assembly now you
need to refer that assembly in your
project to be able to access that class
in the first place and to do that you
need to set the reference ok and to set
the reference just right-click on the
folder and say add reference in the add
reference dialog box on the project's
tab you look at that you can see
assembly one project and introduction to
c-sharp project but you don't see it
here because you are adding you don't
see assembly two in this list that's
because you are adding reference to this
project itself so I select my assembly
one here and the moment I do that look
at that assembly one assembly is added
as a reference to this project
now stir you don't have that error gone
you still have that error so the type or
namespace assembly one class one
couldn't be found
are you missing a using directory or an
assembly reference we are not missing
the assembly reference because we have
already added that then what else are we
we are missing the using directory just
like if you want to access the console
class we have the system assembly here
but if I remove the using directory can
I access that I can't so it's the same
case here you need to use the using
directory so using what is that assembly
one and the moment we do that the error
goes away ok let's go back to our
discussion of access modifier so what
are we doing here I'm trying to create
an instance of our assembly 1 class
which is defined in another assembly and
this assembly one class has got an
internal member and we want to be able
to access this one and let's try to do
that and see what happens when I try to
do that a 1 dot ID look at that first of
all the intelligence doesn't show up
that which means you're not allowed to
access and if you forcefully access that
maybe let's try to initialize that to 1
0 1 if I try to do that and if we build
we will get a compiler error and that
basically is telling us you're not
allowed to access that why because
that's an internal member and if the
member is in to know then it's
accessible only within the assembly
where it's defined you're not allowed to
access it outside of this assembly but
in spite of this being an internal
member we are trying to refer that in
this assembly so this assembly is
different from this assembly and
internal members are accessible only
within the containing assembly NE koude
outside the containing assembly tries to
access that you will get a compiler
error that's what is internal ok now
what is protected in to know ok this is
interesting
protected internal it's actually a
combination of protected and intima ok
let's go back to the slides we know that
a protected member is accessible within
the containing type and the types
derived from the containing type and
what does internal say internal members
are available
within the containing assembly so now
protected internal is a combination of
protected and internal so internal
meaning the member is available any
anywhere within the assembly and if it
is also decorated with protected access
modifier then it means that's accessible
even outside the assembly but those
classes outside the assembly should be
deriving from the containing class and
the containing class can be either in
the same as somewhere in a different
assembly so if you look at protected
internal anywhere so a protected
internal member it's accessible anywhere
within the containing assembly and from
within a derived class in any other
assembly
so even classes within other assemblies
also access this as long as they are
derived from the containing class okay
so let's look at an example which
hopefully will will make it clear to you
okay now here this member ID is
currently in - now let's do this let's
mark this as protected so if I mark it
as protected internal we know that this
member is accessible anywhere within
this assembly one project in the
solution I mean within this assembly one
that's is done by internal but since I
also have protected here which means any
class which is deriving from this class
also can access that and that class can
be in any other assembly so now I have
assembly to another assembly in this
assembly I have this class what I'm
gonna do is I'm gonna make it inherit
from assembly 1 class 1 ok now this
class is inheriting from this class
so obviously this member is protected in
tomorrow so this member should also be
available within this class in spite of
this class being present in another
assembly but then you can't access that
on the instance of assembly 1 class the
way to access that is you can simply say
base dot ID 1 0 1 or what you can do you
can actually create an instance of your
own class assembly 2 + 1 since this
class is deriving from this one from the
principles of inheritance
whatever members you have derived here
will be available to this class so if I
create maybe a 2
and when we say a 2 dot ID you should be
able to access that all right
so so the fact that you have marked it
as protected into now makes it available
within the containing assembly and to
the classes you know even if they're in
some other assemblies they can access it
provided those classes inherit from the
containing class ok that's protected
internal ok so if you look at the
definitions it's pretty clear a member
with internal access modifier is
available anywhere within the containing
assembly and it's a compile time error
to access an internal member from
outside of the containing assembly
similarly a language on Blaine's
protected internal members can be
accessed by any code in the assembly in
which it is declared or from within a
derived class even if the class is
present in none another assembly it's a
combination of basically protected and
internal and if you have understood
protected and internal access modifiers
probably it should be very easy to
follow
all right on this slide you can find
resources for asp.net and C should have
interview questions that's it for today
thank you for listening have a great day