Part 85 Real time example of stack collection class in c# Video Lecture

this is part 85 of C sharp tutorial in
this video we'll discuss a simple real
time example where they stack a
collection class can be used we discuss
the basics of stack collection class in
part 83 of this video tutorial so please
watch part 83 before proceeding these
are the two common scenarios that I can
think of where a stack class can be used
implementing undo functionality in an
application and implementing browser
back button let's say for some reason we
don't want to use the back button that
is provided by a browser instead we want
to have a custom back button within our
asp.net web application let's see how to
implement that using a stack a class
let's flip to visual studio so here I
have a blank asp.net web application
first of all let me add a class file to
this project and let's call it base page
dot CS and I'm going to make this class
inherit from system dot web dot u i dot
page and in a bit you'll understand why
we are doing that okay now as this class
is inheriting from system dot web dot u
i dot page class you know the page class
has onload event so I'm going to
override the onload even handler so
override on load
okay so what do I want to do within this
onload event now in a bed we are gonna
make this base page class the base class
for all of our forms within our
application okay so you know before the
page load event of the respective web
formation work since this is the base
class for all of the web forms you know
the onload event of this base page will
be executed ok and here we are going to
write the logic to create a stack and
then add
the history of the URLs that the user
has visited to that stack so first of
all let's go ahead and create a stack so
URLs are strings so I'm going to create
a stack of strings and maybe let's call
this URL stack and then I'm going to
store this URL stack in a session
variable so session of let's call this
URL stack okay and I want to do this
only if session of URL stack is now so
if the stack is not present in the
session only then go ahead and create a
new stack otherwise you know do not
create it if it's already there okay so
that's the first step we created the URL
stack now I'm going to write some code
here this may not make sense at the
moment but don't worry well it will make
much more sense in just a bit
so if requests so if there is a request
for a web form if the request URL
referrer
is not now okay what does this condition
mean you know if it doesn't make sense
don't worry we're gonna talk about that
in just a bit
and if this dot page dot is post back so
if it's not a postback request and
session off back a button click
equal to now okay if these three
conditions you know if we have met these
teeth these three conditions then what
we basically want to do is you know pull
out the URL stack that is present in the
session variable and then add the URL
refer to that stack okay let me write
that code and then I'll explain that so
from the session pull the stack and the
stack that is present in the session is
of type string and let's call it URL
stack and let's make a copy of this okay
so we pulled the URL stack that is
present in the session variable now what
I want to do is I want to push the URL
referrer absolute URI into this tag okay
now what is this URL referrer if that
doesn't make sense let me explain let's
say for example in my application we
have four web forms now let's say I'm on
waveform one and then once I click on
web form - so we will be navigated to
waveform to the whorl referrer for
waveform - is platform one because we
came to the form - from the form one
similarly from web form to you know if I
click the link on web form 3 then the
URL referrer for web form 3 is wave form
- okay so at the moment let's say I am
on wave form 3 and then if I click this
platform for link that is present on
wave form 3 we will be navigated to web
form 4 so the URL refer for the from 4
is perform 3 ok so basically what we are
saying here is if the URL referrer is
not equal to null and if it's not a
postback request and then if the back
button is not clicked in that case you
know get the absolute URI of the
referal absolute URI means you know we
are going to get everything starting
from HTTP : four slash four slash to the
entire URL basically okay and push that
into the stack in a bit we will see how
we are going to use the stack to
implement the back functionality within
our application okay and then I'm going
to write one more condition here so if
the session of back button clicked not
equal to now then let's add session of
back button clicked to now okay now
there are quite a bit of moving pieces
here
if if this code doesn't make much sense
at the moment don't worry it's gonna be
much clearer in just a bit okay so this
is the base page okay now next I'm going
to add a master page for our application
now master page will give a consistent
look and feel for all of our web forms
in the entire application we will
discuss master pages in a later video
session but let me go ahead and add a
master page to this application so let's
add a new item and let me select master
page and let's call this site dot master
okay so we have a master page here now I
want to design a master page that looks
like this so first of all I need a table
so let me go ahead and include a table
within let's get rid of that new tag and
then let's use a table here and let's
use this style attribute and said first
of all border to one pixel solid black
and then I'm going to hardcore divert to
500 pixels and then I'm also going to
set font family to area all right so
let's close the table and within the
table I'm going to have a tiara and then
a TD and for this TD I'm going to set
call span to two and here I'm going to
use a label control we will see in just
a bit how we are going to use this label
let's call this lvl message and let's
get rid of this text right there and
let's set the full color of this label
to red
okay so we have a label control there
and then let's use another TR and then
first the TD for the first TD within
that TR I'm going to use the style
attribute and then set the width of this
TD 200 pixels let's close that today and
within this TD I'm going to have these
links I'm going to do this in the
masturbate so that every content page
that has subscribed to the master page
will have all these links otherwise
we'll have to repeat these links on each
and every content page so that's the
reason why we are including them in the
master page so within this TD here I'm
going to have another table and let's
use a TR and then I'm going to have a TD
here let's actually make a copy of this
one so I'm going to have 1 2 3 4 okay so
in the first TD of the first TR we need
this text which says links so whatever
you can see here and then we want these
links so I'm going to have an anchor tag
here so anchor tag href equals I'm going
to have the complete URL start
from HTTP so HTTP localhost four slash
and if you look at the name of our web
project that has web forms a demo so let
me copy the name of the project so
localhost waveforms demo four slash
let's say web form one dot aspx and then
let's give it some text which says like
the phone one okay so let me copy this
and then paste it in the other T DS so
this is going to be a form to and the
text say it's waveform two and let's do
that for waveform three and waveform 4
so this is going to be web form three
and iPhone 3 and finally weapon 4 and
this one is going to be that phone for
all right so we have designed this TD
which contains these links next I want
the content placeholder where each
content page can can plug in their
specific content and then I need a back
button again we need back button on each
and every waveform so I'm going to
include that back button within the
master page so I'm going to have another
TD here and then within this today I'm
going to have a back button so let me
drag and drop a button maybe let's name
change the ID of the button to VT and
back and let's set the text on this to
back okay and then along with the back
button we need the content placeholder
ok so I'm going to take this content
placeholder so basically this is the
location where each content page will
plug in their page specific content ok
so at this point we should have a master
page that looks like this
ok so let's actually flip that to the
design mode and you can see it
okay so this is where the content you
know the the content page specific
content will be plugged in so let me
double click this button to generate the
event handler okay so when I click the
back button on the master page what
should happen that's what we are going
to write here so obviously you know if I
have navigated let's say for example
from webform one to webform to and from
there to be from 3 and from there to
before and then once I am on webform for
if I click the back button
I should be navigating to webform 3 and
then if I click the back button I should
go back to that form 2 and then
subsequently to webform 1 okay so let's
write that code okay so if basically
when I click this back button what I'm
going to do here is if you remember in
the master page I mean sorry in the base
page we have the session of back button
click so when I click the back button
I'm going to set this to yes so session
of back button click is yes ok meaning
we have clicked the back button and then
what I'm going to do here is what's the
name of our stack its URL stack within
the session variable so if session off
URL stack if that is not equal to now
that means that it's something within
the session so in that case what do we
want to do we want to retrieve that URL
stack out of the session variable and
then take the first URL and redirect the
user to that URL
okay so URL is of type string so string
that URL is equal to we need to retrieve
that from the stack that is present in
that session variable first of all we
need to pull it out from the session
variable so I'm going to copy this so
start off string let's call it
URL stack equals that and we need to
typecast that to be whatever we are
retrieving out of session you know it
comes out as an object so we need to
typecast it to be of this type stack of
string and then we're going to use the
pop method to retrieve the item that is
present at the top of the stack so we
are going to get the recent most URL
that the end user has visited okay and
then what we are going to do we are
going to redirect the user to that URL
response to redirect to that URL okay
now another thing that I'm going to do
here so once we get this URL stack I'm
going to check if URL stack dot count is
greater than zero okay meaning there are
some URLs that user has visited so it's
okay to pull the most recent URL from
the stack and then redirect the user to
that URL but then if the count is zero
if you invoke pop method what's going to
happen it's going to throw an exception
and we don't want that to happen and
again if the count is zero we know that
there are no pages in the history and we
want to display status message the user
stating there are no pages in the
history so in that case what I'm going
to do and if you remember in the master
page in the first tier we have this
label and the ID of the label is lvl
message so what I'm going to do here is
set the text of that label to there are
no pages in the astray or you can give
any meaningful message that you want
okay so at this point we have
implemented our base page we have
implemented our master page now the next
step is to add content pages let's go
ahead and add four content pages so
right click on the master page add
content page and by default we are going
to get the name as perform one door aspx
and then
what I'm going to do here is on the aspx
page itself I'm going to include an h1
and just say this is web form 1 okay and
in the code behind for I look at this by
default every waveform is going to
inherit from system that web dot u I dot
page okay but we don't want our
waveforms in our application to be
inheriting from that page instead we
won't look at this this is the base
class system root of F dot u Y dot page
is the base class for every web form but
I'm going to make this inherit from base
page class and if you look at our base
page class that is inheriting from
system dot web dot u Y dot page so in
between we have introduced the space
page class because we want to override
the onload event and we want to include
our custom logic here to add the URL
that the user has visited to a stack so
that you know we can implement the back
functionality back button functionality
all right so let's repeat the step to
add you know perform two three and four
so let me right click on the master page
add a content page and that's going to
add web form to and here let me actually
copy this and paste that on web form too
let's call it the sis waveform too so
that we know on which web form BIA and
then within the code-behind file I'm
going to make this waveform to inherit
from base page so let's do that for
waveform three so add content page so
that's going to be perform 3 and here
we're gonna say this is perform 3 and
within the code-behind file platform 3
is going to inherit from base page class
and finally let's add but from 4
so let's change the text - this is five
on four and within the code-behind file
let's make this inherit from base page
all right so all is in place now so
let's go to our base page put a
breakpoint there and see how it actually
works and similarly let's go to a master
page and within the code-behind file of
the master page let's put a breakpoint
in this button back click event handler
okay so let's go ahead and run this now
so I am on waveform 1 so by default we
should land on a waveform 1 but then
since we have breakpoints here before
the webform one page load event has
executed it's gonna invoke the base page
load event and look at this this is the
first time we are landing on this
application so if I step through by
pressing f10 session of URL stack will
be null so when I + f2 it gets inside it
creates a new URL stack and it's gonna
store that in the session variable okay
and then when I press f10 so URL
referrer here is going to be null why
because you know we we directly came to
this URL we didn't come from any other
page so that's why here URL referral is
now and it's not a postback okay so
since URL referrer it's now it's not
going to come inside this condition so
when I + f10 again it's going to come
here our session of back button click we
didn't click the back button so it's not
going to go inside so when I press f5
what's gonna happen we will land on
webform 1 ok now I am on webform 1 look
at the URL I'm on waveform 1 when I
click this link waveform to look at
what's gonna happen the onload event
will get executed again and then session
of URL stack is this equal to null no we
have already created a stack and put
that into the session variable so this
condition is false so it will not go
inside that and it will come here and
check this URL referrer look at the URL
referrer what is that its waveform 1 dot
aspx so where form 1
is referring us to webform - and is this
a postback falls and we have not
condition here falls and falls it's true
and we didn't click you know back button
so this will be null so it's gonna come
inside this block and look at what's
happening here we're retrieving that URL
stack out of the session and at the
moment in URL stack how many items we
have zero items there's nothing in the
URL stack
now when I say push look at this request
dot URL referrer that is the URL
referrer and what is the absolute URI
the full URL okay so that URL now will
be pushed into the stack so once I press
f10 and if you look at this URL stack
there's going to be one item and that is
where from one URL okay so when I press
f10 we didn't click the back button so I
mean it will be now so it will not go
inside
f5 now let me click on web form 3 now
what's going to happen the same thing so
if I come here if you look at the URL
stack already we have but from one dot
aspx now we came to web form 3 but from
where did we come from web form - so the
URL rivera is performed - so we're gonna
push that into the stack so when I press
f10 and then if you look at this URL
stack look at that perform - is on top
of web form 1 so let me press f5 here
and then let's go to web form 4
okay so same idea let's press f10 come
to the URL stack here so within the URL
stack we already have performed one
waveform - now we are on the form for
and to waveform for we came from web
form 3 so here URL Reza is going to be
perform 3 and that will be pushed into
the stack so f10 and if you look at this
URL stack we're gonna have a form 3
there okay so let me plus a 5 and we are
on web form for now when I click back
button what's gonna happen let's look at
that so I click the back
so when I am on waveform 4 and when I
click on back button - which waveform
should be navigate - we should go back
to webform 3 okay so we should go back
to the recent item within the history so
that's why we need to pull the item that
we have added last to the stack okay so
that's why we are using stack here so
when I click back button look at that
the onload event is executed
so if session of URL stack it's not null
so it's not going to go inside URL
referrer it's not going to be now okay
but then is this a post back true so we
are saying if not is post back only then
come inside so it's not going to come
here inside this block and when I press
f10 and session off back button click
you know we click the back button now
but that even hasn't been executed yet
because page load event will be fired
even before the postback event okay so
when I press f10 session of back button
clicked will still be now and because of
that it's not going to go inside now
when I press f5 it's going to go to that
back button click even handler within
our master page and then look at this we
are setting that session variable back
button clicked - yes
so f10 and session of URL stack is it
Nala no so it's going to go inside
retrieve the URL stack from the session
and URL stack dot count is definitely
greater than 0 and then look at this URL
stack what is the item that is present
on top of the stack web form 3 and when
we use pop method it's going to retrieve
the item that is present at the
beginning of the stack which is nothing
but webform 3 so when I press f10 it's
going to come here retrieve the top URL
from the stack which is performed to e
and we are going to rewrite the user to
that webform and when we do a
redirection what's going to happen the
page load event of webform 3 is going to
be fired again okay so let me plus a 5
look at that it is going to come to the
onload event again now I press f10
session of URL stack you know it is not
null so it's not going to go there and
the new RL refer
is live from four but then this is not a
postback request so it's going to be
false so these two conditions are true
but this condition is false because we
have clicked session I mean back button
so session of back or back button click
will not be equal to now okay look at
that session of back button click if I
take this and then go into the immediate
window look at that we have s in there
so it's not going to go inside but here
you know since it is not equal to now
it's going to come here and set that to
now and now when I press a 5 what should
happen we should land on webform 3 okay
so let me disable all the breakpoints
here and now when I click back button
from webform 3 where should we go to
waveform to look at that and from there
we should go to their form 1 look at the
URL as well and now at this point all
the items would have been removed from
the stack so when I click back here
what's gonna happen there are no pages
in the history so we could the output
that we expect all right so this is a
very simple example of using stack class
to implement our custom back button
within an asp.net web application that's
it for today thank you for listening
have a great day