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You know what's up everyone mark right here at the slopes dot com and we've done some really cool stuff

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in our apps so far we've gotten the user interface built.

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We've got segues so you can go back and forth between screens.

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We even now got a model built and re-actions tied to our league Visi and we don't let you go onto the

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next screen unless you've selected an option which is really cool.

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And then the data of course is stored in the player model.

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It's a struct.

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And so the next thing and possibly last thing we need to do here is actually pass data between View

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controllers.

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Now this is a topic that a lot of people struggle with and then they've done some really weird things

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to get data talking between View controllers are going to make it really easy for you.

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OK.

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And the function that we're looking for here is already built in your view controller whenever you create

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a new one and it's called prepare for Segway.

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OK.

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And when you read a function by the way.

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OK.

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When you get the actual function name.

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All right.

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It's going to look like this.

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Prepare for Segway.

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So this right here is the name of a parameter and this is the variable name that the parameter is going

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to take on.

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And so this this and this all kind of compose of the function definition of the function name.

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And if you have other subsequent parameters those will also be added to the name of the function and

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to show you what I mean.

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So this is right here all nice ready for us.

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But if I type in the word prepare OK.

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Notice how it says prepare for Segway interface builder sender it's all right there boom OK.

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So that's the function definition.

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OK.

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And it's an override function meaning the default view controller that you're inheriting from We'll

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call this and we don't need to call super on this or anything like that because we're overwriting it.

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Typically what that means is when you are writing and you don't call super.

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It means that you don't need the view controller implementation of it you don't need that code to run.

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Our code is going to take over from here.

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Otherwise super would call that parent code.

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OK so what we want to do is we want to see which side we were going to again remember what I said.

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I said if you have multiple segues that can be triggered from a single controller you can need to check

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which one is which.

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And you might pass different data to different segues.

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OK.

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In our case we only have one so it makes it really nice but we're still going to have to write the same

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code we would write if there were multiple segues.

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And this is the code.

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So if let And let's just say skill B C equals Segway destination as skewl B C.

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All right.

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Let me let me break it down.

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OK.

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So what we're saying here is we're doing it if let's sequence and went and flipped sequences.

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OK.

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Basically it will try and run an operation.

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OK will try and run the statement in this case it's going to try and assign the destination view controller

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into this variable or this constant.

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The lead is a constant.

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OK.

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So it's going to try to do this if it succeeds it will execute inside the code block if it fails then

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this statement will fail.

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OK.

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So if Segway that destination so were the failure could happen is right here.

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As the as with the question mark is saying let's grab the Segway destination.

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Well if you look at here at this destination by command click it destination is of type you view controller

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so it's just a generic view controller.

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But our destination that we want to go to is the skill of these you know skilled VC does inherit from

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you a view controller.

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And so with object oriented programming we can downcast a skill VC or rather a destination view controller

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as a skill AVC because it does inherent.

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But let's say stewe skill AVC did not inherit from you view controller it was just her own class then

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this would fill but it won't in this case.

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So what we're saying here is let's grab the destination that we're going to go to so it checks the Segway

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for the destination view controller.

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So the skill Visi in this case.

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OK.

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And then it's going to try and grab it.

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So it's going to grab the view controller code that exists what's in our storyboard.

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So this file right here OK it's going to load it in memory it's going to try and it's going to grab

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it.

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And of course it'll work because that's what's designed to work and it'll grab this code right here

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and it's going to send it back to you and store it here in this variable.

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OK.

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And to prepare for Segway happens whenever a Segway is triggered this prepare function is going to be

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called so it lets you do things before the Segway actually loads on the screen.

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And this is where you will pass data between controllers.

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So again what we're doing here is we're saying it's the skill we.

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So if we can grab it successively then we're going to do something again and we had multiple controllers

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that you could choose from let's say there was five different screens you might go to based on the selection.

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Then what we would do is we would have like if let you know and then you know else if let And then we

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would say you know other VC.

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And then we would cast a different Visi and then it would go down until it finds the proper one.

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And then we send the data.

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OK.

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So we're grabbing the next few controller we want to go to.

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And if this is confusing to you it's OK.

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You're just learning this takes time.

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You're going to do this many times over and you can always watch this video again.

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OK.

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So grab the skill we see and what we want to do we want to pass data into it.

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So what we're going to need to do is store a player variable in our schedule VC and we don't have one

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yet so let's do that now.

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So over here let's go ahead and say var player type player and let's do an pleasantly unwrapped optional.

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What that means is no matter what we promise we promise that there's going to be code in there.

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It's not going to be nil.

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OK.

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And so that's what we're promising.

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And so what we're going to do is we're going to go over here and we are going to say skill Visi player

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the one that we just created OK and not save the file.

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Skill it up player there we go.

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Now it's popping up.

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OK.

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So skill it up player equals player.

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You're like what's going on here.

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These names of the same.

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Well we are referring to the player that we saved and this new controller here.

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OK.

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This is here in league visi.

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We've set the player here and what we're doing is we are just passing this player from the screen onto

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the player on the screen.

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So literally this is where the handoff comes you know like footballs being handed off UK same exact

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thing we're handing off the data from the player on the league.

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And we're storing it in the player in the skill of the sea.

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Now something really important to understand when you are in prepare for Segway this will always always

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always always be called before you did load is called on the destination view controller.

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So remember this very important prepare for Segway is always called before you did load on the destination

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view controller.

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So what you can do is you can always guarantee that data will be available in view to load if you initialized

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it.

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So if I was to do something like this player datt desired League.

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OK if I was to do that it will not be Neal.

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It can't be OK.

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And it says expression implicitly coerced from string.

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Now here in our player model it's because we have them as optionals And you know probably here we should

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have these as implicitly unwrap the optionals as well too because we have to have data in order for

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this to happen for this APTA run and this can be very confusing.

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OK.

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Do I make it optional do I make it implicitly unwrapped optional so remember this.

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OK here is the rule.

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If you can promise that data is going to be there I mean your app must have data in order to run.

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Then you can make it an implicitly unwrapped optional.

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If you don't know whether data is going to be there or not and that's part of your design.

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OK.

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It must be an optional.

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OK so if you are promised data is going to be there because your app can't run without it you can assume

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it's going to be there and make it implicitly unwrapped.

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If there was no data in here and you tried to access it yes it would crash but you're promising that

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there's going to be data there whereas the optional saying well might application design means that

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there might not be data.

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Maybe it's optional field who knows.

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So that's the rule.

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And again it could be confusing.

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It takes lots of practice but you'll get it.

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So this morning should go away and there we go.

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And so what we're doing is we're going to print this here so let's just go ahead and run our app and

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see if it actually prints as expected.

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So what should happen is we're going to select the desired League.

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OK.

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We're going to go to the next screen and when the next screen loads we print it should show the desired

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league that we selected.

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Hypothetically if we wrote the code correctly

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OK.

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So get started.

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Let's go ahead and select the women's league.

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And when I click Next I should see women's printed here on the screen and sure enough it was.

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OK.

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So are you with me so far.

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What happened was we triggered her segue.

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So right here.

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See this performs segue.

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We triggered that from the next button right.

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And we said let's load the skill AVC So this is called.

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And then the very next thing that's called is prepare for segue.

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And this is where we pass data from this view controller into the next using this code here and we set

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the data that we need.

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And it doesn't have to be in this very well we could call the function that sets it in a variable but

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somehow some way we need to set data on the destination view controller then the destination view controller

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which was the skill AVC in view to load our data is already ready to go.

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And you could print it and use it accordingly.

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So we've kind of just built the app right.

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What we've done is we built an app that has three screens.

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We've learned how to set data from some filt we selected a field we stored in a model and then we pass

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that data model between View Controller so we can use it and you could continue to do this.

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We could call another performed from Segway and another prepare and pass it on to the next one and pass

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it on to the next one and then the next one.

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Now if you're thinking that's a lot of work do we really want to pass data from view control of your

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controller.

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And I would say no later on you're going to learn how to work with some different design patterns like

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the singleton pattern where you have a central source that holds all your data.

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And that's a lot nicer than passing things through.

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But this is a very common practice as well too.

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And this is in the Apple documentation we've done everything exactly as Apple teaches in their documentation

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and it's very useful So that's it for now.

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This is really good stuff.

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Core foundational things that you need to know everything that I've taught you on the swish app.

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You have to know it now.

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And if you ever want to get a job in industry you have to know everything we've done in this app by

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heart.

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OK.

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There's nothing overly complex but the things that we have learned here you have to know by heart in

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order to get a job if you don't if you don't know these things that are in this lesson you're not ready

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for a job yet so you're going to need to master these very basic principles because this is what you're

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going to doing most of the time in your app development.

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So that's it for now.

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Marc price at Dev slopes dot com.

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Movin on and forward.