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Add subscriptions to your TodoList with RxJava.
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Next let's modify the listener we
used to add items to the to do list.
0:00
So we can see here, in our main activity,
we had a call to find you by ID,
0:05
setOnClickListener, and
in that callback we'd get our onClick.
0:10
The first thing we're gonna do is
we need to get the actual text
0:14
from our addInput button
which is an edit text.
0:18
Then we wanna make sure it's not
empty we don't want to add empty or
0:23
no items essentially to our list.
0:27
So we needed to check that and
then we added the actual item to our list.
0:30
Finally we clear the input
in the editText and
0:36
we dismissed the keyboard
using these two lines here.
0:40
So we're gonna use this instead of
0:43
onClickListener call back we wanna
convert this into be an observable.
0:47
So we are in observable
it's going to emit items.
0:52
So what we essentially want here is we
want every time an item should be added
0:55
we want to a emit it out.
1:00
And so we're gonna transform
this listener and these checks
1:02
into a set of callbacks as an observable
and then we're gonna subscribe to that.
1:07
And whenever we have a valid
item to add to our list,
1:11
we'll be able to add it to our
list just like we did before.
1:14
So let's start by doing that.
1:17
The first thing I wanna do is we're
gonna use the Rx bindinds library
1:20
that we have added as a dependency.
1:24
And there's something
in there called RxView.
1:26
And RXView is a helper for
1:30
handling any interactions with base
view types so just the basic view class.
1:33
And so
one of those things is handling clicks.
1:38
So we can see here that
RxView.clicks takes in a view and
1:42
it returns back an observable.
1:46
And we can subscribe to that observable
and notice it's of type void.
1:48
That's because the subscription we get
is going to emit an item every time that
1:53
view is tapped or clicked,
similar to the onClickListener.
1:59
So let's go ahead and
use the same button we were using before.
2:04
And it's helpful to know when things
are tapped but we also can take that and
2:13
then before we get to the subscriber,
2:18
before we get to the observer,
which we pass into the subscribe method,
2:21
we're gonna first transform this
click into the actual data we need.
2:25
So the actual data we need in the end
is a to do item to add to our list.
2:30
So the first thing you wanna do is first
every time a click happens, let's map it.
2:36
So we can call .map and
2:43
RxJava is really great because it uses
this nice syntax where we can keep
2:45
calling different operators after
we create the initial observable.
2:50
So here I'm adding a map operator and
what we want here is a new function.
2:55
And what we want here is we're
2:58
gonna transform our click into a string.
3:03
And that string is gonna be the text.
3:09
So just like down here where we were
calling addInput.getText toString.
3:11
What we're gonna do is we're
going to have a call and
3:17
for every click that's
the void that happens for
3:25
every click we're gonna return back
the add input get text to string.
3:27
So now,
if I were to subscribe at this point,
3:38
I would be getting items that are strings.
3:42
I would be getting the text that are
strings every time the button is clicked.
3:47
But we also are doing this check
to see if it's empty or not.
3:51
So we can also add an additional
operator to check for
3:55
that as well and
that we can use filter for.
3:59
So here I’m gonna to provide another
function and what this functions gonna do
4:03
is takes in our string and
then it returns a Boolean.
4:08
And what the Boolean means is if it's
true we're going to emit this item.
4:12
If it's not true this
item won't be emitted.
4:17
So what we're essentially
doing is checking here, and
4:21
the thing we're checking
is if this is empty or not.
4:24
So let's go ahead and do this check.
4:28
So all we have to do is say, the string
ass that comes in so the string ass,
4:34
is going to be emitted
through the map function.
4:39
That's gonna be a text from the input box.
4:42
And in here if it's not empty,
we're gonna go ahead and
4:44
allow it to be emitted
from our observable.
4:48
And that's exactly what we want.
4:52
So finally we can subscribe to this.
4:54
And when we subscribe, we're gonna go
ahead and provide an action again.
4:58
We don't care about on completed or
on erroring this case.
5:02
We just care about when those items are
emitted because they're valid items to be
5:07
added to our list.
5:11
So when an item is finally admitted,
we'll get it in this call and
5:16
what we can do is exactly
what we were doing before.
5:21
And now we can delete this entire
findViewById setup listener business
5:34
we were doing before.
5:39
And we can see that, using RxJava,
and these nice wrappers in RxView.
5:41
We can really build out functionality so
that our subscriber here
5:48
in our subscription only receives
calls when it has valid data.
5:55
We don't have to do additional
error checking here, and
6:00
this is really helpful because while we're
inlining, the subscriber right here.
6:02
It could be the case that there's
a totally different class or
6:08
object, that is going to be the observer.
6:11
And In that case, you won't have to worry
about doing any of the is empty checks, or
6:15
getting the text.
6:19
It is only going to get a call
6:21
when a string is ready to
be added as a new TodoList.
6:23
So it really does simplify things here.
6:27
And what we'll also see is that,
because we added our subscription and
6:30
our subscriber to our TodoList and
our adapter.
6:34
Last time,
every time we add a item here to our list
6:38
our adaptor is automatically gonna be
updated with this new item in the list.
6:41
So that's just gonna happen for us,
6:45
we don't have to worry about it
because this subscription is set up.
6:47
So here we took our button,
6:51
we transformed it into an observable
when clicks or taps happen.
6:54
And we filter that data, and
made sure that we only emit items
6:58
when they're valid, and when we do emit
items, finally can add those to our list.
7:03
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