C# Xna Made Easy Tutorial 11 - Single KeyPresses Video Lecture | C# Game Development: Game Making made Easy (English)

hello you see sharp excellent users I'm
welcome to your next tutorial I know
this tutorial never came for a while but
now you can look forward to this
tutorial let's tutorials going to be um
covering a very important topic but
often overlooked topic and it's about
single key presses now a lot of people
don't teach single key presses because
they figure that you can figure it out
on your own but um sometimes it could be
a hard a hassle learn how to do it right
so I'm going to teach you exactly how to
do single key presses with XNA now I've
worked with a lot of different graphics
libraries and by far xn8 sway is the
easiest because it has the perfect
built-in functions to allow you to do
the to detect single key presses so to
show you how to do it we're going to
have um a string called cat um I'm going
to name a text and the values the movie
show so when we press down the button
when we only press it is going to show
our texts I'm a display show and we
release the button then it's the text is
going to disappear so we're going to be
learning about pressing down keys and
detecting the releasing and keys and you
might be saying why do I detect releases
well it could be very useful in certain
situations especially if you're working
with say the mouse until you're making a
paint program and you say that when you
click arm say you're drawing a line you
click to start pulling the draw the line
you hold it until you dragged to a
certain point and when you release then
it ends up drawing the line right so a
release is not a more common one
normally detect four key presses for
single key presses but sometimes you
want to detect for single key releases
so um let us get into the code so then
after that or we have a boolean variable
called displayed text which is equal to
false so basically the text will not be
displayed to the screen right now and
then now we have
arm we created to keyboard states are my
key key state or we can say that the
current key state but i'll set the key
state that is the actual key that you're
pressing i didn't keep watch a previous
key state which is equal to the key
state that happened last update and then
we have our load we're creating a sprite
fonts to display our text so an
initialize nothing we load in our load
content we load our sprite font um now
an update this is where we actually
detect for single key presses so um we
already know about the function is key
down and that's a very great function
because it detects for continuous armed
attacks of the key is pressed down for
every single frame or every single
update and that's cool but um that's not
good for single key presses because when
you the the update method will update
probably 60 frames per second right
which is what you really ideally want in
the game so if you press down if you
press down the down key for a second it
like it will detect that so many your
time it will detect that as 60 frames it
will detect that you've pressed it 60
frames or 60 times because of um because
of the timing that you pressed it if we
were able to like press down the button
and release it in like say less than a
millisecond or a millisecond then it
wouldn't matter but for now we only want
to detect it as though the button it was
only pressed once and then it won't
detect it after again so what we do is
that we set previous key state is equal
to Key State so this is what previous
key said is what happened the last frame
and then this up this time you said key
state equal to keyboard I get state so
the new keyboard value right so then
right here in our if statement we say
that if II if key state
down is equal to keys down so if it's
equal to the down arrow key but the
preview and the previous key state is
equal to ki up and no is key up um the
down key so to make that to make it make
more sense uh if if previous key state
um if before the last frame you weren't
pressing the down key then this is true
that means it was up and um if this
frame you were actually pressing the
down key then this is true meaning
you're pressing down so if this is true
and this is true then we move that we
have pressed a button now you might be
saying how is this detecting single key
presses we'll look at it this way so say
last okay say we never press anything so
we just start the program so you never
pressing the thing Sookie state arm is
equal to null right so each time updates
key state is equal to null now I'm this
update it goes through this line and
since previous key set is equal to ki
state and key set is equal to long so
previous key state is equal to null then
it goes here but we're actually pressing
the down key this loop Sookie state is
equal to keys down so previous case n is
equal to no but this is equally keys
down so saying of the key if the
pre-press down is um down and if the if
the down arrow key isn't being pressed
then display text equals true right so
say we say behold you say we're holding
down the down arrow key right we loop
again so previous keiki state is equal
to ki state therefore meaning that
previous key state is equal to keys down
and since we're still holding down the
down arrow key key state is equal to
down so this statement is true this time
around but this statement is not true
because the key that the down arrow key
is being pressed so that means this
won't be this arms if state will be
false and that's why I will only detect
the single key press now if I was to
release the down key and I press it
again then the statement would be true
again and therefore only two takes the
text one key press if that makes sense
to you now we have an elsif right here
and it's a complete opposite so I switch
this from is key down to esky up and
switch this from esky up to sq down and
what this will do is check for key
release so if the down key is released
so if you're not pressing the down key
then I will set the temp display tax
equal to false meaning that the text
won't show up on the screen anymore and
then the draw function simple and or the
draw method simple enough we say if
display text is equal to true we draw it
to the screen um and let us run this to
see what we get so in our game window we
see nothing right now but if i press it
down arrow key it shows up now i'm
holding it down arrow key right now and
i once I release it then it doesn't do
anything and I mean it disappears the
text disappears when I hold it it stays
on when I release it disappears so on
and so forth so I hope you enjoyed this
tutorial on next tutorials gonna be on a
single mouse on presses and like yeah
I'm a single mouse state or whatever its
exact same way to do it just using the
mouse state but for those of you who
just want to just to see me do it then
I'll show its you in the next tutorial
so thanks for watching this hope you
enjoyed it and by