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Yo what's up everyone.

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Mark Price does slopes dotcom.

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And let's continue building our app here.

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We're making great progress.

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We want to do next is actually have this product screen show and we want to get our collection view

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all configured etc. etc..

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So first things is we need to make sure we have an identifier on our Segway So click your Segway and

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then add the attributes inspector over here.

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Set an identifier.

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I like to just set this to The View Controller that we are going to which I believe is the product B

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C category as we said we haven't created it yet.

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Well we should do that and then we'll set the identifier.

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So in your controller folder Let's go to a new file cocoa touch class and instead of you a collection

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B-cell we will say you view controller and we will call this products beseem press Enter create.

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OK.

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Now go back to the main storyboard here.

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We'll select our view controller will change its class to the products ABC wonderful.

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And then on the segue here now we can set the identifier to products and we see it there.

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OK.

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So the Segway identifiers in there.

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Let's go back to our categories Visi and what we want to do is when a category is selected like tapped

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we want to show another view controller so really all we're doing here is presenting a Segway and then

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passing the appropriate data into the other view controller that we're going to be going to how do we

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do that.

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Well the Table View delegate has a really cool function called did select row index path.

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One thing that's really important is that you don't accidentally click did de-select so did de-select.

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Ok that's when they've selected and taken their finger off a lot of new developers actually entered

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this in and then the table view is not working correctly when you're tapping it.

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So we want did select row index path.

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OK.

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So we're going to have roads going to tell us which row is tapped.

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And then we can build out some logic here.

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No big deal.

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So first things first is let's grab the appropriate category that was tapped.

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So let category.

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Category equals data service.

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Get categories and data centers get categories and we're going to say Index path dot row.

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OK.

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So we're just grabbing the category.

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You know I think it's good category.

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Now that's correct datasource get category it's trippin out it's just trippin out here.

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I'm just going to copy what we have up here because this one has been out X code and it's trippin.

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So there's our category.

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Wonderful.

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And then what we want to do is say perform a segue like so with identifier where we know it's the products

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Visi Segway and the sender basically will object.

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We want to pass in this.

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So when I prepare for SEGUI is called We have data available to us and this is where we pass in the

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category so we're passing in data here into our perform Segway.

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So then when prepare for Segway called we can then pass that over into our products and then sell it

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to the prepare for Segway function like so.

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And you've done this before if let products be C equals Segway destination as products.

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So we're describing the destination View Controller and we're casting it into the appropriate view controller.

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Okay.

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And then what we'll do is we will set the category on that view controller but we don't have any variables

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or anything for that yet.

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So what I want to do is go to my products Visi get rid of this comment here.

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And what I want to do is see what it did receive memory warning is its great function here called initialized

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products.

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Okay.

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And then what we'll do is we'll pass in.

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Well what do we want to call this exactly initialized products for like a category title like will pass

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in a title or just pass and the whole category.

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Just thinking aloud here.

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Okay initialized products category.

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Wonderful.

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And then what we'll do here is we'll actually store a list of products so same as we've done before

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private set.

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And then it's if I can type public var and this one is going to be called products.

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All right.

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And it's going to be an empty array type product like so if you're wondering why we're making this an

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empty array.

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And the reason is let's say that we the data hasn't loaded yet you're getting it from the internet somewhere.

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Well you want an empty array to base your collection view off of Otherwise it was just nail your collection

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if you would look for an item and it in your whole app would crash.

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So that's why we're creating an empty array here.

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OK.

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And what we're going to do here is simply use the function that we already built in our data service

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to get the appropriate product for this category that we are passing in.

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OK so what we're going to do is we're going to say self-direct.

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So don't you say self-heating to say products equals data service and since dogs get products for category

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title we're going to say category title.

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So it's going to happen is our products are going to be populated with products and we're just passing

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in the title that was passed in the categories we see here to the products see.

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And so now this initialized products function we can actually call from right here so we can say products

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AVC dot initialized products and we can pass in the sender as a product or category.

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There we go like so

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OK.

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So what we're doing here is we're grabbing the products Visi and we're just calling that initialized

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products function that we just created.

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Sender you're like what descender center is just the category that we passed in so remember up here

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Pyrenean ended select ROA index path we passed in the category to the sender.

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All we're doing here is grabbing the sender because when you pass it in the parameter type is any like

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any object.

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And so we have to specify that this is a category so sender as category and why am I force in wrapping

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it.

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Because I know for a fact that it is a category because I just said it right there.

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OK.

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So you can be sure that this is going to cast correctly.

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So products these initialized products sender as category.

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Okay.

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And one thing that we probably want to do here is create an assertion so at build time we know that

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this is working correctly.

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And then I'll feel more comfortable using that force unwrap.

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So let's do that now.

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We're going to say assert that sender as with a question mark category is not equal to nil.

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Okay.

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And this assertion is good because what it's going to do is at build time this is only for build time

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in developed motets not for production.

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What's going to happen is this assertion is going to be called and it's going to say it absolutely must

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be of type category when we cast it and if it's not it's going to crash your app at build time.

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As a developer so as a developer you're going through you're building your project and then you go in

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here and then your app crashes you know that you need to fix it we're forcing a crash here if it's not

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working.

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So at runtime it will definitely work.

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OK this is just a layer of protection in your development that will help you out.

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Now you maybe you think it will mark why didn't you do a guard statement in the casting OK or why didn't

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you do an if let if let sender as category.

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Well the reason I didn't do an if LET or guard is because my application requires this to be a category.

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It's not chance ok it's not user base where it might be a category it might be something else.

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Ok if that was the case we would use the guard or an inlet.

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But since my app requires that this is a category when we cast it it makes more sense to use an assertion.

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So build time.

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If it's not working it crashes our app which is what we want.

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OK we can guarantee it.

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No.

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So I feel a lot better about force unwrapping the this or forecasting this here so we're initialising

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the products center as category.

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This is great.

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And then in the products you see it's going to go ahead and set the products to the products that we

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have here in our data service.

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So the next thing we need to do is get our collection of view actually working so let's implement a

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couple of protocols put a comma after you have your controller and we're going to use a collection of

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view delegate and UI collection.

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The new data source like we've done before.

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And of course we need the outlet for our collection of use at Iby outlet weak var and we're going to

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say products collection of type you collection view.

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OK.

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And we're putting the exclamation there at the end.

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Meaning it's an implicitly unwrapped optional.

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And it's saying hey you haven't implemented the function so click the red button up here.

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Do you want to add protocol stubs.

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Absolutely.

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So command X protocol stubs will put them where they actually belong down here I get to get rid of the

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available nonsense.

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And this year the code and get rid of that there.

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OK.

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And what we do here and feuded load is we will say products collection that datasource equals self and

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products collection.

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Delegate equals self.

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OK we are saying that hey this collection of view is going to be the delegate and implement the protocols

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the appropriate protocols to get this working OK.

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And so a number of items in section.

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Now there are multiple.

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You could have an app with multiple sections a collection view or table view.

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In our case we only have one.

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So what I'm going to do is just simply return products that count.

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Otherwise what you might have done is you might have said if Section equals 1 then you return three

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you know.

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Or.

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Well you know whatever number it is or some other collection.

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Else if Section equals to return this many.

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But in our case again we only have one section so we're going to return products don't count and then

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sell for item index path.

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This is very similar to what we've done with the table view.

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OK we're simply going to say if let.

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Sell equals collection view.

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Dick Hugh reusable sell.

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And this one's going to be the product sell.

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I think that's what we called it or what we will call it if we haven't done it yet for index path.

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And in this case it's looking for the index path that's being passed in right here from the function.

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So there's our cell if let's sell.

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And then what we want to do in the cell is just passing the data that we're going to need.

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And so let's look at our cell product sell and we don't have a way to update the data here so let's

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create our function to do that.

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So function update views and we're going to pass in a product.

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We've done this before with the table view very similar.

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And what we'll say is we will say product image image equals image named.

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And this is going to be product image name and then product title text equals product that title and

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product price text equals product price.

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So all we're doing here is every time a collection of cell is created or Decoud we're going to pass

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in the appropriate product and update the view.

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So it's showing the correct data.

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And this is important because of views on a collection of cell and collection of you and a table of

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you are recycled.

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So we have to continually update the views.

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OK.

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So that looks good there.

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So back in our products we see what we can do now is we can grab the appropriate product and then pass

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it into the cell so we can say let product equals products index path dot Roe.

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Okay we're grabbing the appropriate Roe for the products and we're storing for the product and we're

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storing it here in this product constant and then sell that update views.

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We forgot to cast it.

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So let's cast it now so as it were and say product sale.

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There we go now it knows it's a product sell.

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Once I sell that update views and we'll pass in the product and then we will return the cell as the

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function requires.

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Otherwise if this didn't cast appropriately like when we converted the cell it didn't it wasn't a product

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cell which could happen if you had like a head or cell or some of you had multiple different types of

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cells for a single collection which you can maybe you have one cell that looks one way for a certain

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type of data and another cell it looks the other way you might have two collection B cells.

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In our case we only have one but we still need this statement here or rather that you don't even need

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an else statement.

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We could just say return and then we could say product cell because it would never get here if you made

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it through this portion here.

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OK.

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So great.

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We are creating a cell or two cuing it we're passing in the appropriate product so it updates the data

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and then returning that cell that looks fantastic.

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And we got our products collection view here which I think even though it says it's been set I think

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it's not probably set back in the storyboard here.

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Select your controller right click it and you see that product's collection is definitely not set it's

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lying to us.

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Let's drag it over there.

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OK.

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And then let's also make sure our cell has a reuse identifier so go to your product cell and it does

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not give us a reuse identifier.

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And we are going to call it product cell.

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You have to have this so the cells can be reused.

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OK.

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Let's go ahead and give this a spin.

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Let's just see where we are.

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See for even runs I'm feeling good about it so far.

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We could have forgotten something though.

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OK.

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Moment of Truth when we click one of these.

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We should see the next screen load.

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And it does show the appropriate data.

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I'm going to click hoodies and it's working so we've got our hoodies Dove soaps logo gray red gray and

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black so our data is definitely populating as expected.

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A couple of things.

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Is this coater swag is really annoying and it's not supposed to be there.

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The design that our designer gave us was just the arrow itself.

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And also there's not a title here.

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I think we need a title to show what kind of products it is and what kind of products we're showing

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rather.

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And shirts.

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So you know it looks pretty good and I kind of like it.

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Yeah yeah yeah yeah.

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I like it.

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So let's let's fix those couple of things.

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So what we'll do and this is empty which is great.

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So what we'll do is we'll get rid of this text here and then will set a title.

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So let's get the title first.

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So what we'll do is save this in the products we see when we're initializing this data.

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Here let's just go ahead and set the title.

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And that's easy as simple as saying navigation item Daut title equals we'll say category title so to

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grab the title of the navigation bar.

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OK all you have to do is grab navigation item that title and it knows how to find it and then you set

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it to the title here that is.

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That's really easy.

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The harder one is the button and you would think maybe you would do something like this navigation item

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that let's say back button right here or backbiter button item and then you know oh look at the title

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we can set the title like this equals you know let's say an empty string but it doesn't work.

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Unfortunately it does not recognize this because the the back button actually belongs to the previous

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few controller.

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OK it does not belong to this one and belongs to the previous one.

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So we have to do is actually go into categories visi.

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OK.

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And what we can do in the categories we see is we can just set it here and prepare for segue.

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All right.

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So we can right here create a bar button item so bar button equals you IVD bar button item you have

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to create a new one you can't modify it.

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Again like I said It's strange you think you could but you can't.

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So you create a new one.

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And what does one say bar button title will make it an empty string and now will say navigation item

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back bar button item equals bar button.

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Or place what's there with something new.

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OK.

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And you know I think I want to do this before I initialize anything just for good measure.

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Like so

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cool.

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So we've just created a bar button item.

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We said it with an empty title.

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And then what we've done is we've set the navigation item back bar button item to this new item here.

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So let's go ahead and see if that works shirts and says shirts at the top and has the backbone Kaino

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TX which is great hoodies so hoodies hats say hats.

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Prices are different everything this is really good.

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What you've done here is very important.

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OK.

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If you can if you don't have everything memorized that we've done in this series on this app then you're

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not likely to get a job as as an Iowa developer and the reason why is displaying data is so critical.

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OK and we've written what I call good clean code.

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So if you write code like this you'll you'll impress people.

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And what we've done is we've worked a table use reusable cells.

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We worked with collection use which our grid system again collection of can go horizontal if you want

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to swipe horizontally.

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You could let's say that you wanted Let's say that you wanted to be able to swipe horizontally here

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but swipe up and down here maybe this.

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Maybe we just had one page and this said hats and the said shirts what you could do is you could actually

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have a table view and each cell inside the table is actually a collection view OK with a horizontal

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scroll.

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So the table view goes vertical.

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But the collection below goes horizontal.

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And so you could have this row here on the table you cell which is a collection of you it goes from

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left to right left or right left or right.

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And that's how you would build something that goes up and down and left and right which is really cool

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of course.

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The collection itself can also do that functionality so you can do a collection view within a collection

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view.

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And we did a grid spacing here the spacing was automatic for us.

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You can change the spacing you can change the layouts and do some other nifty things.

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We didn't even begin to cover all of that here but you can change all that.

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And this has really come together you've learned how to host data in a data service using the singleton

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pattern.

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OK one instance of this class in memory you've also learned the basics of implementing the delegate

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pattern which is you have classes implement some type of protocol.

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And I will abide by these rules.

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And once those protocols are implemented X code will force you to implement the code needed for it such

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as sell for item index path etc. and then you implement those things.

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You have to make sure you set the data source and delegate on your table view or collection of view.

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Otherwise your app will not run appropriately.

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A lot of new developers do that so you'll learn a lot of things here.

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This is the basis and foundation of what you're going to do whenever working with data.

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And we've taught you everything here the right way.

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OK the Apple way and I'm I'm happy.

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I think it's good.

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So congratulations.

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This is good stuff here.

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And let's move on and forward two other amazing apps Mark Price at deps slopes dot com.

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See you next time.