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Everybody what's going on this is Caleb with slopestyle.

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And in this video we're going to talk about observables and observables are sort of the foundational

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building blocks of our acts and our swift and so in order to begin.

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Go ahead and pull open your tricks playground.

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The one that we built in the last video and before we began we're actually going to go ahead and select

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all these other playgrounds because we're not going to use them.

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And I'm just going to actually move them to the trash sometimes X code gets grumpy about that.

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But all you need to do is reopen X code as you can see it just crashed.

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And I'm going to go ahead and pull it open again.

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There we go.

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And now we have just our singular playground.

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So let's go ahead let's start by talking about observables.

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Now everything in our ex-wifes is either an observable sequence or something that subscribes to events

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emitted by one of those observable sequences and that might be a lot of jargon and a lot of words maybe

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you're not familiar with but I'm going to show you how it works.

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We're going to start by creating our first observable case so let's just go ahead and type let number

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sequence equals observable and in order to create an observable for a single value you can type observable

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not just meaning just this one thing.

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And let's go ahead let's pass in the number five.

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OK.

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So now we have an observable with a value of 5 K that's pretty cool and the coolest thing is that it

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can infer what kind of observable this is so I want to show you one other thing you can type maybe let

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number equals observable.

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And using these brackets you can go ahead and set it to have an explicit type.

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But the cool thing is with swift type inference it allows us to infer that type automatically.

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And of course you could have gone in and you know done just what we did here with an integer not just

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that would create the same thing but no need to if Swift can infer it.

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So very cool although it is helpful to know if you need to create a specific type of absorbable maybe

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for C.G. float or for another type of value.

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So that is how we're going to create an observable.

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Now I want to show you how you can subscribe to this observable and do something based on how the values

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change.

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Or in this case how they have been added.

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So let's go ahead and let's say let number observer or maybe subscription.

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And we're going to set that to be equal to number sequence.

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But what we're going to do is we're going to call DOT subscribe.

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OK.

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And we're going to subscribe to number sequence.

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That means that we're setting up a property that's going to be able to monitor what happens in this

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observable sequence.

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But there are a couple different things we can do upon subscribing.

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OK so I want to show you that you can see here subscribe is on NEXT ON ERROR uncompleted and on disposed.

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Now on next basically means when a value comes in.

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So if I add five here on next would be called after on next is called If there's no error on completed

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will be called.

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And so I want to show you how these work what we can do is for.

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Well you know what let's just do on next first.

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And so I'm going to actually get rid of all of this and just type on next.

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And then we're going to do a closure here.

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So basically on next we're going to print whatever the value is and in order to get into that we can

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use the dollar sign zero.

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And what that's going to do is it's basically creating a temporary variable and it's cycling through

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this sequence of one value.

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It's only a singular value and I'll show you how to make an observable of multiple values in just a

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moment.

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But for now what we can do is we can print out whatever is in here.

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Now you can see it prints out five down here at the bottom.

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What if I were to change it to 10 it would print out 10 k.

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So observable that justice for making an observable of a single value.

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And we have subscribed to it.

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Now did you notice the number sequence by itself doesn't do anything.

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Only when we subscribe to the sequence and call on next or on completed or on disposed will it do something.

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Now that is really interesting to know.

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And we're going to see how some of these other capabilities like on completed and on Error work.

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So let's create a new sequence.

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Let's go ahead and type let.

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Hello.

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Sequence equals observable.

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And we're going to use a new function.

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We're going to use observable from.

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And as you can see it's looking for a sequence or an array.

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So I'm going to go ahead and select the one that's looking for an array.

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And we're going to give it one.

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So type in some square brackets there and we're going to create a string for each character in hello

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like so h e l l o.

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And so now we have an observable that is observing this array we have created an observable from an

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array.

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That's what from as for now in order to do something with this we need to subscribe to this observable.

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So let's go ahead and type let Hello subscription wups subscription equals Hello sequence that subscribe.

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But what we're going to do is we are going to basically use our subscribe on call here and we're going

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to switch through all the different cases that can happen to see what happens in a normal subscription.

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So go ahead and press enter and we're going to call this event and we're going to make a switch that

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will switch through all the potential outcomes.

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So go ahead and type switch event and we have some cases here.

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So type case and let's see what is possible for us to access we can access next.

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We can access error.

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Okay.

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Remember on next on air case completed Okay.

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Now for each of these cases we need to do something.

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So for case next we're going to go ahead and print but we need to know what to print.

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We're going to create a variable here or a constant rather that can capture the value of whatever event

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is happening so go ahead.

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And in parentheses here we'll type let value and we can print out value.

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So remember on next we printed out the value here and it printed 10 right.

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We're going to do the same thing here except we're going to print out the individual characters in our

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observable because remember it's an asynchronous sequence.

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Pretty cool.

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Now for Aero we're going to do the same thing we're going to type let error and we'll print an error

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if there is one for completed.

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We don't need to print anything we just basically need to know we're done subscribing so we're just

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going to print what's inside the parentheses we'll print completed.

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So now that this is done.

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Watch what happens.

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As you can see we are going through our subscription here and we are printing the value of every next

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event.

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So what is happening is we are going through this and next or on next is being called We're printing

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the value so we're cycling through the first element in our array is H then E then L then Elvan o.

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And then when it's finished we are printing completed so you can see that every sequence once it gets

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to the end uncompleted is called unless there's an error and then the error would be printed which of

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course you could do something with.

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So that is just one way that these observable sequences are very very cool.

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You get a lot of really great control over what you're doing.

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And so these are just two ways we can create observables and we're going to be talking about different

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kinds of observables in the next section of this course.

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And they're called subjects.

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They're like observables but they work in specific ways so some are better for some things and some

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are better for other things.

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Now this is just a basic intro to observables and we're going to talk a little bit more about them in

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the next video and the video following that.

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But by the end you're going to have a good understanding of observables as you can see we are observing

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a certain value we're subscribing to that value and we can do stuff with the values inside by simply

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calling dot subscribe.

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Now in the next video we're going to talk about disposing.

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And that's part of the memory management part of our ex-wife that we need to to be on top of.

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But don't worry it's really easy.

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So let's go ahead and head over to the next video where we're going to talk about disposing an observer.

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I'll see you there.