iOS 11 Developer Course Tutorial - App (Is It Prime Part II) Part 20 Video

so now that we've written our code to
work out whether a number is prime or
not we're going to build the app itself
and as always this is gonna be a
challenge for you so do your best to
build it but handedly but don't feel bad
if you need to follow along for some or
even all of the video the important
thing is to give it a go and try your
best so here is our simulator hope you
can see I'm trying out some values
already so we've got a title this time
I'm using a placeholder to instruct the
user what to do into the text view and
then we've got our button and our result
label as we've seen before
so now it was very simple if I put in a
5 it tells me it is prime if I put in
597 it's not prime if I put in for it so
not prime as well but this time we also
get a nice error message so if I don't
put anything in then it says please
enter a positive whole number similarly
if I put in 3 and characters for example
I get that error message as well I have
to put in a proper whole number as
digits to get a result it's impossible
to crash this app moreover I've also
applied auto layout to this app so it
looks good in both landscape and
portrait so I want you to apply that as
well from what you've learned from a
couple of videos ago and our press
command right to get us back into
portrait orientation so best of luck
start of course with a new project I
hope it goes well
all right here we go them I hope you
managed to do most of that yourself but
I'm gonna start of course with file new
project and as usual
we'll go for single view application and
I'll call it is it prime and I'll avoid
the question mark again and save it on
the desktop and then we'll start over in
main storyboard and this is where we'll
add our labels and everything else and
it's also where we'll set up our
constraints and auto layout so let's
have our central title label is it prime
make it a little bigger and center as
usual and I'm going to fix the top
constraints of the distance from the top
of the screen is fixed set the width and
height and also Center it horizontally
in the container excellent
next
I'm going to add a text field and this
one I'm going to stretch out to the very
edge of the screen and I'm going to set
the constraints to be top left and right
margins which means it will be aligned
to the is it prime label and it will be
at that distance from the edge of the
screen regardless of screen size and
then I just need to set the height as my
fourth constraint there we go all
looking good and to keep our user
interface super clean and tidy I'm gonna
add a placeholder enter a number to see
if it is prime there we go so I could
have had that as a separate label but
actually it works pretty well as a
placeholder in the text field next we're
going to bring in a button which will
ask the question is it prime and again
we'll set the top constraint width and
height and we'll also set the alignment
has horizontal in the container and
finally we'll bring in our label which
I'll stretch to the edge again Center
the text set the top left and right
constraints and set the height to be
fixed great so let's have a quick look
does it look good in other orientations
it certainly does everything is where we
want it to be smaller screen size is
work great bigger screen size is now the
text field is perhaps a little large on
the iPad but that is at least doing what
we told it to
so I'm happy with the auto layout now
let's bring in how assistant editor to
create our IB actions and IB outlets
so first off I'm control dragging there
to just underneath where it says class
view controller and we'll call this the
number text field then control dragging
from a button I'll call it is it Prime
and that's going to be an action and
then we'll have as we've had before the
result label there we go and I'll get
rid of the text there until we add it in
wonderful so now we can get rid of the
assistant editor go back over to view
controller dot Swift and write our code
so the first thing we need to do is to
get the value of the text field and
attempt to convert it to an integer so
let user entered integer
equal number text field dot text and
we're going to try the to convert that
to an integer and actually it's asking
us to force unwrap the number text field
text field itself which normally I would
be quite happy to do because we know
that this is a text field so it will
definitely have a value even if that
value is an empty string so if the user
doesn't type anything in there it's
still just going to be an empty string
so normally I'd be happy to do that but
because we've just looked at optionals
and better ways to unwrap them i'm going
to be a bit more careful than usual and
do an if let and we'll call this user
entered string and we'll set that equal
to number text field dot text and only
if that works will we attempt to convert
user entered string to an integer so
we're being super careful here i would
normally be very happy to force unwrap
this but this is being very careful and
there's no chance of a crash in there at
all okay now
let's carry on and see if this
conversion to an integer has worked so
again we'll use if let and this time i'm
going to use number to be equal to user
entered integer so if we get to here
we've definitely got a number that we
can work with if we don't then this time
i'm going to give a little error message
to the user so we'll set result label
dot text
to say please enter a positive whole
number there we go if they have entered
a positive whole number though then
let's bring in our code so we don't need
to define the number this time because
we already have it so let's paste that
in and now that should do the check on
their number and we can finally look to
see if is prime then we'll set the
result label text to be the number is
prime and if it's not we'll set the
result label text to be number is not
prime I don't think that's quite
deserving of an exclamation mark so I'm
gonna leave it as is okay let's switch
over to the iPhone success simulator and
take a look so we're being really
careful here we're checking to see
whether the number text field has a text
value which we're pretty certain that it
does then we're checking to see if we
can convert the user entered string to
an integer here and this one I'm not so
sure about because the user may well
have entered a letter or something
completely different so if they have
done that we're going to send them a
message asking them to enter a positive
whole number and if they haven't then
we're going to go through the process
and work out whether their number is
prime
okay let's take a look so let's play the
game first and try for example hey six
is it prime 6 is not prime correct
what about 61 61 is prime also correct
19 is prime excellent so we're looking
good let's just try what happens if I
put in an empty value then we get this
message brilliant if I put in a 1 I get
correctly one is not prime and then if I
type in the number three like that I get
please enter a positive whole number
wonderful
so that's exactly how we wanted this app
to work it's pretty simple and pretty
basic but it uses a lot of the skills
that we learned in this section and it
could be useful to a schoolboy or
schuylkill working out prime numbers in
a maths lesson but that takes us then to
the end of this section I hope you've
enjoyed it and you'll be pleased to hear
that we're gonna spend the rest of our
time in Xcode and specifically in the
next section we'll be looking at some of
the more advanced features like timers
tables permanent data storage
controlling the keyboard and we'll be
finishing up with completely working
versions of a to-do list app and hey
what's the web app so there's a lot to
learn I look forward to seeing you for
it in the next section