JavaFX Java GUI Tutorial - 13 - Listening for Selection Changes Video Lecture | JavaFX Java GUI: Learn to build Powerful Applications - Front-End Programming

alright guys welcome back and in the
last tutorial what I did is I showed you
guys how to create a simple choice box
in other words a drop-down list and what
we did is we pretty much had it set up
where the user could choose some kind of
option such as meatballs and then
whenever they click this button it
looked in the drop-down list extract to
the value and then you can do whatever
you want with it however did you ever
see those types of applications where
you don't need to click a button to get
the data for instance if you want to
change the background of this app right
here on maybe other options were like
red blue green so on and so forth as
soon as the user clicked one of these
options the background would change so
if you actually try doing that in JavaFX
you would come across some issues and
the issue is this we were on this again
now whenever the user clicks one of
these it doesn't emit any event in other
words you're just going to say whenever
the user clicks arm I'll show you guys
where is all right right here
so whenever you click the button you see
that it creates an event so that is an
event that's something that happens and
you can run code directly from that
however changing an option or selecting
an item in your drop-down menu that's
not an event at least not to JavaFX
however we can get around it by adding
something called a listener to this
drop-down menu in other words we can
stick a little bit of code on here and
then once we do that it's going to be
listening or waiting for the user to do
something so if we want to do that we
can actually get rid of this method
because remember this is the code that
happened whenever the user click the
button and we're not going to be worried
about the button right now and we can
also get rid of this right here so I'll
keep the button on the screen right here
but it just won't do anything for this
tutorial just because I don't feel like
deleting it up all right
so in order to pretty much simulate
omitting an event whenever the user
clicks or chooses one of the
items Lily listen for armed listen for
ya selection changes alright what we
first need is a reference to the
drop-down menu choice box you tighten
this up it annoys me having two lines
between art now the method that we tack
on this is get selection model now there
are different kinds of ways you know how
I told you guys that drop-down list is
one list there's also like a tree and
I'll show you guys another list in the
next tutorial but basically different
types of lists have different types of
selection models whenever you're using a
drop-down list you can only select one
item however there are you know some
other lists for example you see how I
selected two items in here that's
another type of selection model again
really don't need to worry about the
different types right now but I just
want to explain you guys what get
selection model means now once you have
that you call a method called selected
item property now of course this is
essentially just the selected item the
item that they choose has properties on
it in other words just think of this is
the item that the user selected from
that list now once we have that we can
add a listener so what the solicitor is
going to do is it's going to sit on
pretty much um your item and it's going
to wait for something to happen in other
words what's the one thing that you can
do oh you know with menu items you can
click them so whenever that event occurs
it's going to emit three parameters so
just like before remember whenever we
use lambdas what happens is it's pretty
much a short condensed version of a
function and your parameters go on the
left-hand side and the body of the
function or the code that you want to
execute goes on the right-hand side
so whenever the user chooses the item
from the drop-down list we actually pass
in I don't know if all right so it's not
popping up out of
TI's the old value new value all right
so it's going to toss in three
parameters this is essentially just on
the list item itself or the property I
think V stands for observable this is
always in the documentation but this is
pretty much the property of the item
itself this is the old value so if you
had Apple selected and you're removing
the bacon this would be apples and of
course the new value would be the new
item that you selected
so again if you're going from like ham
to meatballs this would be the list item
this would be him and this would be
meatballs so now whenever they select a
new item I'm just gonna let's say print
something on the screen and actually if
we go now keep it right here all on one
line all right so system.out not Pitt
out print line and we'll just print the
new value or the item that they selected
all right that looks pretty good let me
go ahead and run it and check it out so
again we have Apple selected by default
let me go to ham prints out ham let me
go to meatballs prints out meatballs so
again this is occurring before I even
click the button actually when I click
the button nothing happens so if you
ever want the functionality to do that
then there you go and again just to
demonstrate what the old value is the
old value is the item that was selected
before so if I have Apple selected and I
select bacon then it prints out the old
value so there you go
but anyways that is how you listen for
changes on the drop-down menu boom
roasted see you guys later