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So previously, we got up to the point where we used and NSUserDefaults to save our data, and then we
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created a data model that represented each and every to-do list item so that we can associate each item
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with not only just a title, but also whether if they have been done or not done.
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So this way, every single time we reload the table view, it will always be up to correctly assign a checkmark
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or no checkmark to each and every to-do list item.
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Now previously, where our app fell down was when we tried to save data that is of a custom data type to our
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to our to-do list.
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And the reason we mention was because we're using NSUserDefaults which can only take standard data
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types, not any custom types or custom objects that we have created.
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So in this lesson, we're going to address this by using a different method for saving our data and persisting
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it on the device.
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So the first thing that we need to do is to delete this print statement inside our AppDelegate
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didFinishLaunchingWithOptions so that we don't get confused between our print statements. And then if we're
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going to go into our TodoListViewController
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and we're going to create a file path to the Documents folder,
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so just super.viewDidLoad,
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we're going to create a constant called dataFilePath and this is going to be set to equal FileManager,
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which is the object that provides an interface to the file system,
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and then we're going to use the default FileManager which is a shared FileManager object.
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So this, you should now recognize, is a singleton. And this singleton contains a whole bunch of URLs and they're
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organized by directory and domain mask.
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So the SearchPathDirectory we need to tap into is the documentDirectory.
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Now, be careful here, you're not looking for the documentationDirectory,
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that's something entirely different.
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We're looking for the documentDirectory.
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So have a scroll through what other things you can tap into.
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And once you're done, go ahead and enter .documentDirectory. And the location where we're going to
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look for it is inside the userDomainMask.
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So this is the user's home directory, the place where we're going to save their personal items associated
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with this current app.
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And because this is an array, we're going to grab the first item, and then we're going to print this
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dataFilePath.
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So let's go ahead and run our app and see what we get back.
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Now, if we have a look inside our debug console, we can see that we've got this optional printed which doesn't
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really matter because we haven't unwrapped the optional URL, but this is what we want.
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This is the file path that we need.
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So let's go into Finder and navigate to this location.
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So if you want to navigate up the directory, you can always use command up button and you can go up the
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hierarchy until you get to the root which is your Macintosh hard drive.
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Now, starting from here, we're going to go into Users, then my current user which is angelayu, and then
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we're going to go into Library, and we're going to go into Developer. And inside developer, we're going
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to go into CoreSimulator, and we're going to look for the device that is 8D49. So you can always click
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on Date Modified, so that it sorts by last open or last modified.
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So here we go, 8D49, and then inside data, inside Containers, inside another folder called Data,
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there's a folder called Application, and we finally get to our application which is this one 53A.
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And you can see here we've got a plist that represents our NSUserDefaults.
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Now, inside our app, instead of using NSUserDefaults and grabbing that singleton and saving our data
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to that address, we're going to create our very own p list file.
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So all we need to do is go to the part where we created the file path to our Document's directory, and
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then we just need to use the dot notation and tap into the appendingPathComponent method.
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And here, we can add a path component, you can call it anything you want, but it's good to name it something
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that makes sense.
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For example, in this case, maybe we'll call it items.plist.
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Now, if I run the app and chase down that file path,
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and you'll see that we haven't yet got the items on plist. We've merely created a path to this new
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plist that we are going to create right now.
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So let's head back into Xcode.
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So let's head back into Xcode and let's modify our code. So instead of using use a default, we're going
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to create our own plist at the location of our data file path.
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So the first thing that we have to change is this line where we set our itemArray for the key
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TodoListArray into our UserDefaults.
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And because our itemArray is an array of our custom Item object, then this line fails
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and this is when our app crashes.
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Now, instead of doing this,
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so I'm just going to delete that line,
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I'm going to now create something called an encoder and the encoder is going to be a new object of the
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type propertyListEncoder and I'm going to initialize it.
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Now, what I can do is I can say, let data = encoder
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so that's that property listing code that I just created which will encode our data namely our
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itemArray into a property list.
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So we're going to use our encoder and we're going to use the method encode, and the value that we're
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going to encode is our itemArray.
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So once I hit enter, you'll see a couple of problems, namely that the encode method can throw an error.
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So we know what to do.
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We, first, have to create a do block, and then we need a catch block.
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And finally, we need to mark this method with a try. And because we are inside a closure, i.e., the part
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that gets triggered once the user presses the Add Item button, then we have to mark all our properties
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with a self.
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Now, once we've encoded our data, the next step is to write the data to our dataFilePath,
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and this is also a method that can throw errors,
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so we have to mark it with a try also.
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So try data
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.right,
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so writing the data to a location and the location is, of course, going to be a dataFilePath.
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So in order for us to access it there, we have to put it out here as a global constant.
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And so now we can say dataFilePath. And inside the catch block, we're going to print "Error encoding
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item array" and we're going to print out the error that triggered it.
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And finally, we have to mark this with a self because we are, again, inside a closure.
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So the last thing we have to do before this is going to work is we have to go into our Item class and
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we have to mark our class as conforming to the protocols
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Encodable.
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And this means that the Item type is now able to encode itself into a plist or into a JSON. And for
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a class to be able to be Encodable, all of its properties must have standard data types.
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So things like strings, Booleans, arrays, dictionaries, they all work, but not if you have a custom class
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in here.
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So let's hit save and let's fix that.
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one last issue. And let's just comment out this line so that we can address it later.
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Now, if we run app, let's see what happens.
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All right, so let's add a brand-new item.
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So all three of these items got initialized because we hardcoded them and added them to the itemArray
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which is what we're loading up inside our tableView.
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Now, in order to test out our code and see if our encoding worked, we have to press the add button and
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we're going to create a new item.
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And once I hit add item, you can see that I've got no errors, my debug console didn't pop up telling me that
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my app has crashed, and my app is continuing to work.
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and it now contains that brand-new list item.
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So if we go back to Finder and check out that previous location that we found,
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but remember last time when we checked in here, there was nothing inside, it was completely empty?
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Well, now that we've actually saved something.,
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but now that we've actually uncoded itemArray and wrote that data to that dataFilePath, we now have
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this plist.
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And if we have a look at it by double clicking, you can see that we've got a whole bunch of items that
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have been organized and encoded automatically using our Swift encoder.
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Now, it's important to note at this point that, previously, when we were talking about UserDefaults and
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I explained why it is that we're unable to save an array of custom item objects, it's because the plist
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can only accept a limited number of data types, and that pretty much the standard or foundation types.
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But if you take a look over here at our encoded Items.plist, you can see that, firstly, it's an Array
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with four items, whereas UserDefaults is a dictionary or a bunch of key-value pairs.
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And that's what we always said about UseDefaults.
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But if we expand this route, we can see that our encoder has very cleverly encoded each of the properties
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into a dictionary, and the individual properties still conform to all of the basic data types.
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And this is why even though that both plists are Items.plist is able to save our custom item objects,
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but the NSUserDefaults is not, and it's all down to the encoder.
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And if I have this live next to my app, if I add another new item-- That's really really imaginative of
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me. You can see that it shows up here,
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but it also shows up here, right?
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But this one bug, when we tried to check our items off or uncheck it, this done
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property is not updated in our Items.plist.
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So let's have a look at why that might be.
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So I'm going to stop the app and we're going to look at the part where we try to save that property.
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So you can see here, this is where we've got that Delegate Method,
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didSelectRowAt indexPath.
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And inside this method, we toggle the item at the current index path,
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it's done property to the opposite of what it used to be.
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So this is only reflected inside our item of range.
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So how can we save this information to itemArray.
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Well, we have to use the same process, i.e., let encoder = PropertyListEncoder to encode the data,
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and try and write the data to that dataFilePath,
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and if there's an error, print an error, and then reload the data.
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Now, instead of copying all of this and pasting it over there,
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this is a good time to think about creating a save data method.
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So let's go ahead and create a new function code saveItems underneath our IBAction.
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And inside this function, we're going to copy all of this code.
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We're going to cut it
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and we're going to paste it inside save items.
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So, now because we're no longer inside a closure, we can get rid of these selfs in front of our itemArray
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and dataFilePath, and we can also simply call saveItems, both when we add a new item using
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the AlertController, but also when we toggle the checkmark.
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And we can delete this as well because it exists inside saveItems.
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So, now let's hit run and see if our app works.
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And now if we check on the first cell which is "Find Mike," you can see that this automatically updates
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inside our Items.plist and all the changes are reflected live.
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But there's still a bit of an issue here, namely, where are the items that we saved earlier on? Where's the "Save
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the World" item? Where's the "Add a New Item" item?
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Why is it not showing up in our to-do list?
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Well, that's because even though we've written the saving part of the code which encodes our itemArray,
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we haven't yet written the code to decode our items.plist in order to populate our table view.
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So that, we're going to tackle on the next lesson.