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All right.
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So how did that go?
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I hope you gave it a go.
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And you now have a working CategoryViewController that works as you expect it to.
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Now, I know I'm repeating myself, but if you haven't given it a go, do it now.
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Don't watch the solution video first, because then you can't prove to yourself that you really do understand
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it.
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So I'm going to presume that you've given it a real good go and you're just here to check and make sure
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that you've got it right.
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So if we have a look at our To Do list view controller, the first thing we have is this variable itemArray
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that contains an array of NSManagedObjects created using the item entity.
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Now, over here, we'll need something similar.
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So let's create a variable called categories that is going to be an array of Category objects, and we'll
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initialize it as an empty array.
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The next thing we need to do is we need to grab a reference to the context that we're going to be using
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in order to create, read, update, and destroy our data
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and this is gonna be the thing that's going to communicate with our persistent container.
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So the context is going to be equal to our UIApplication and we're going to grab the shared singleton
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app instance, and we're going to tap into its delegate property, and we're going to downcast this as
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a AppDelegate object, and then we're going to tap into our appDelegates persistentContainer variable,
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and then we're going to load up the viewContext for that persistentContainer.
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If any of that was confusing at all,
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make sure that you have a look back at when we first wrote this line of code, and also the animations
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where we walk through how this worked.
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Now, the next thing is to setup our TableView Datasource Methods,
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so we should know the required ones by now,
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right?
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It's table view numberOfRowsInSection and we're going to return,
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of course, the number of items in our categories array.
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So return categories.count.
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All right.
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So onto the next obligatory table view delegate method which is tableView cellForRowAt indexPath
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which is here, cellForRowAt indexPath.
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So here we are going to--
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So here we are going to dequeue a ReusableCell withIdentifier for indexPath.
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So this creates a reusable cell and adds it to the table at the index path.
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So the identifier is a string. And let's just go back and check what we called it and we called it 
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CategoryCell.
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So I'm just gonna copy and paste it into here as the identifer and the index path is, of course, the current
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indexPath that the table view is trying to load up.
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Now, once we've created our reusable cell-- Now, once we've created our reusable cell, we got to set the
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cell's textLabel.text property and we're gonna set it to equal categories at indexPath.row,
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and we're going to tap into the category's name property or name attribute that we created earlier on.
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That property gets automatically generated because we added it as an attribute.
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And finally all that's left to do is to simply return the cell, and it will be rendered on screen.
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Now, the next thing I'm going to work on is the addButtonPressed IBAction, and here we're going to
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create a new alert which is going to be created from a UIAlertController and I'm gonna use the initializer
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that takes a title which we'll call "Add New Category," message, we'll leave blank, and the preferred style
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will just be alert. And then I'm going to create a action = UIAlertAction.
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And this also takes a title which is going to be the word just "Add." That's gonna be the name of the button.
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The style is just going to be default action and I'm going gonna select the placeholder for the handler
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and hit enter so that it creates this completion handler for us.
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I'm going to name the alert action just action.
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We're not really going to use it. And I'm going to delete the code placeholder.
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Now, inside this completion block or closure is where we're going to specify what should happen once
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the user clicks that add button.
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But before we do that, we're going to say alert.addAction and the action we want to add is the one
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that we created just now.
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And we're also going to setup our text field. So we do that using alert.addTextField, and we're
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going to hit enter on the configuration handler, and we're going to call our text field just field.
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And once that new text field has been created and added to the alert, we're going to store a reference to it
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by creating a variable called textField which is going to be a new UITextField object, and then we're
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going to set that textField to be equal to the field that is created inside our alert. And then we're
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going to set the textfield's placeholder to maybe something like "Add a new category."
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And finally, we're going to say present, view controller to present is the alert view controller, animated:
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true, completion: nil.
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Okay.
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So, now it's time to address what should happen when the user clicks on the Add button inside the alert.
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Well, this is where we have to create a new NSManagedObject and that is going to be a new category.
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So let
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newCategory = category.
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Now, notice how this also a type alias called OpaquePointer that also has the name category.
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So make sure you don't pick the OpaquePointer, pick our category instead, and also double-check the data
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type by option clicking on category afterwards.
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And we have to create our category by specifying a context. We've already created a reference to our
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context at the top of our file.
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So that's the one we're going to use.
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And by the way, if when you option-click on your category and Xcode tells you it's a OpaquePointer data
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type, just surround the word 'Category' with backticks like this,
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and that should solve the problem. But because we're inside a closure, remember, we have to write
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self.context in order to refer to that variable. Now, we're going to set up the new category, newCategory.name
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is going to equal to the 
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textField.text
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So whatever the user entered into that textField inside the alert is gonna be the name of the new category.
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And then we're going to grab a reference to our array of category objects by saying
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self.categories.append,
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and we're going to add this newCategory to the array.
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And finally, we're going to call saveCategories.
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And this method, of course, doesn't exist which is why it's not being highlighted.
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So this is a good time to go into our Data Manipulation Methods section over in the middle here and
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add that function saveCategories.
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And now Xcode reminds us that, of course, we need the "self" in front of saveCategories because we're
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inside a closure,
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and then it changes color to reflect the fact that it recognizes what we're talking about and which
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method we want to use.
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So inside our saveCategories method, I'm going to try and commit our context to our persistent container
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by saying context.save. Now, because this throws, then I'm going to hold it inside a do catch block
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and I'm going to log or print any errors that it catches, so "Error saving category" and the error is error.
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All right.
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And finally, once we have saved successfully, we're going to call tableView.reloadData so that our
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table view updates with our latest data.
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Now, the last thing that we have to do is we need to call a method called loadCategories
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when we first initialize our CategoryViewController. and that also does not exist,
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so we need to add that over here. I'm gonna create a function called loadCategories.
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And inside here, we need to read data from our context. And to read data from our context,
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we need to specify a request and we need to specify the data type of the request as a NSFetchRequest
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that is going to return an array of category items.
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And this is going to be equal to a broad request,
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so we want to grab all of the category objects.
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So we're going to say Category.fetchRequest, so we get back all the NSManagedObjects that were
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created using the category entity.
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So now we're going to say try context.fetch and we're going to fetch back all the results that fit
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our current request.
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And if our fetching of our requests succeeds, then we're going to save the output or whatever gets returned
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from this method into our categories array.
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So we can say categories = try context.fetch(request). And because this method can throw, then it's
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a good idea to trap it inside a do catch block where we're going to print and say there was an 
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"Error loading categories" and this was the error code, an error message. So, now all we have left to do is we
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have to tell the tableView to reload the data using our latest version of categories after fetching
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all of the category object.
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So let's give our app a go and see if all of that code works.
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Cool.
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So we're bringing up a blank table view because, currently, we still don't have any categories. And you
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can confirm that if you go into the SQLite database.
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But if we add some new categories, let's say, I don't know, Shopping List, maybe another one called Home,
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and one called Work, and maybe one called Miscellaneous.
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Okay.
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So we now have four categories. And we can check to make sure that they are indeed being persisted using
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Core Data by double tapping the home screen, terminating our app, and going back into our app.
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And as you can see, they are still exactly where we left them.
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So our code has succeeded.
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So if you had any problems setting up your code up to this point, then it might be worth going back to
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your code and seeing if there's any errors or bugs that you can fix.
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Now, in the next lesson, we're going to set up our Table View Delegate Methods, namely, what should happen
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when we click on one of the category cells, because when I click on home, I wanted to take me to a table
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view that contains all of the to-do list items that are associated with the home category.
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So for all of that and more, I'll see you on the next lesson.