Async and await in C# example Video Lecture | C sharp: Enhance your Skills (English) - Back-End Programming

this is part one zero one of C sharp
tutorial in this video we'll discuss the
use of async and evade keywords with an
example so here is what we want to do we
have a notepad here which has some data
let us create a simple windows forms
application that counts the number of
characters that we have in this notepad
let us assume the file is very big and
it takes around five seconds to read and
count the number of characters in the
file when the process file button is
clicked we want the application to
display processing file please wait
message so the user knows the
application is busy processing the file
as soon as the application finishes
processing the file it should display
the number of characters as you can see
here another important requirement is
that the application should remain
responsive throughout the entire process
that is when the application is busy
processing the file the application
should not hang and we should still be
able to interact with the application we
should be able to click within the other
controls on the form move the form
around on the screen resize it if
required etc first let's create the
application without using the async
innovate keywords and see how it behaves
what I have done so far is created this
notepad with name data dot txt within
this notepad we have caught some text we
want to read the number of characters
that we have here this data dot txt
notepad is present in the data folder
which in turn is present in C Drive I've
also created a new windows forms
application to create a new windows
forms application click on file new
project and within the new project
dialog box select we should see sharp
and you'll see VIN as forms application
I have named this windows forms
application async example and on this
windows form I have a button and I have
set a few properties on this button
first of all I have set the name of the
button to be TN process file and the
font size to 10 and then finally the
text on the button to process file
this forum we also have a label and here
is that label for the label I have set
name to LVL count this is the label
which will be displaying this message
processing file please wait and then
once it has finished processing the file
the number of characters that we have in
the file so I have set the name of the
label to LVL count and again font size
to 10 and finally text to an empty
string and for the form itself I have
set text property to count characters in
a file now let's go ahead and generate
click event handler for the button so
select the button and then within the
properties window click on the events
icon and then click on the click event
here which is going to generate the
click event handler method now let's
right click on the form and view code so
here we have the click event handler so
the first thing that you want to do here
is create a method which is going to
process the file and count the number of
characters with a notepad so this is
going to be a private method it's going
to return us an integer that is the
number of characters that we have in the
file and let's name the method count
characters this method is not going to
take any parameters the first thing that
we are going to do here is create a
variable count and initialize it to 0
the next thing that we want to do is
create an instance of streamreader
which is going to read the file from the
disk and the stream reader Clause is
present in system dot IO namespace so
let's bring that namespace in and now
let's create an instance of stream
reader let's call it reader equals new
stream reader and we want the stream
reader to be pointing to our notepad so
let's specify the path for our notepad
our notepad is present in C Drive within
data folder and the name of the notepad
is
dot txt and then now let's create a
string variable let's call it content
equals reader dot read to end so this
method is going to read all the contents
of the notepad and we are going to store
that content in this variable and to get
the number of characters all we have to
do is on the string variable use the
length property which is going to give
us the number of characters and let's do
that within our count variable now our
notepad is not that big so this
application is going to take a few
milliseconds to process that to make the
application look busy for five seconds
let's make the thread that is processing
to sleep for five seconds
so first let's bring in system dot
threading namespace and then let's make
the current thread sleep for five
thousand milliseconds which is five
seconds and then finally let's return
whatever we have in our count variable
so this is a the private method which is
going to count the number of characters
that we have in our notepad now we want
to call this method with another click
even Handler so here let's create a
variable I'm going to call it count
let's initialize that to zero and the
first thing that we want to do here is
within our label let's display the text
which says processing file please wait
and then you know let's call over count
characters function which is going to
process the file and remember this is
going to be busy for at least five
seconds
and then as soon as it finishes
executing this method within this
variable we will have the number of
characters that we have in the notepad
which we want to display in the label so
LBL count dot txt equals count dot to
string and to this lets append
characters in file all right so let's go
ahead and run our application by
pressing ctrl f5 we have our application
running here when we click this process
file button we are going to have two
problems first of all it will not
display the status message processing
file please wait and the application
also becomes unresponsive while it's
busy processing the file will not be
able to move the windows form around
like this and we also will not be able
to resize the form while it is busy
processing the file let's actually look
at that in action let's click the
process file button notice we don't see
the status message I am NOT able to move
it around and I am not able to resize it
as well once it has finished processing
now I am able to move it around and we
can resize it as well and now we see the
number of characters that we have in the
file and here is that blocking example
code that we just discussed now let's
see how to make this windows forms
application responsive by using the
async and evade keywords the only method
that needs to change is this BTN process
file click method let's make this method
async by using the keyword async so
basically this is telling we can call
this method asynchronously and then
within the method we are going to create
a task you can think of tasks as a unit
of
to do this task class is present in a
different namespace and that is systems
or threading dot tasks so make sure you
have that using declaration now we are
going to use this task to call this
count characters method this is a method
which is going to take a bit of time to
execute so we are offloading that
responsibility to this task
now since this count characters is
returning an integer we are actually
going to create tasks of integer let's
call the instance task equals new task
and we want this task to execute this
count characters method so let's pass
the name of the method here and then
let's start the task so this task now is
going to execute this count characters
function and while the task is busy
executing the count characters function
the UI is free and the user will be able
to interact with the form you know the
form will no longer be blocking we'll
look at that in action in just a bit
so we have our task which is executing
our long-running job here which is count
characters and then another change that
we need to do is right here so when the
application has reached at this point
you know we have to wait for this task
to complete
right so to signal that we are going to
use evade keyword and we are going to
await on the task so right here the
application will wait for the task to
complete processing count characters and
then return and at that point we'll have
the number of characters in the notepad
which they UI will then display in the
label so three simple steps here to use
our async and await keywords and make
this application responsive let's go
ahead and run our application by
pressing ctrl f5 we have our application
running and when we click this process
file button notice the status message
processing file please wait is
immediately displayed and the
application is also
Responsive look at this when the
application is busy processing the file
I can move it around and I can also
resize it so here we have a non-blocking
responsive application we have of a
non-blocking example code that we just
discussed right here so what is the use
of async and await keywords in c-sharp
async and await keywords i used to
create asynchronous methods the async
keyword specifies that a method is an
asynchronous method and the evade
keyword specifies a suspension point the
evade operator signals that the async
method can't continue past that point
until the awaited process is complete in
the mean time control returns to the
color of the async method an async
method typically contains one or more
occurrences of an await operator but the
absence of our ate expression doesn't
cause a compiler error if you have any
experience writing multi-threaded
programs then you might get a few
questions at this point can we achieve
this using threads what is the
difference between a thread and a task
and when to use one over the other we'll
answer all these questions in our next
video thank you for listening and have a
great day