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So, now that we've confirmed that our refactoring works as we expected, the next step is to reintegrate
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our app with UserDefaults so that we can try and persist
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our item objects using UserDefaults.
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So, now let's delete this line of code where we were using to debug previously, and let's reactivate our
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defaults to try and retrieve our items out of our itemArray.
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So before we do that, we have to make a few fixes, of course, because we're no longer retrieving an array
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of strings, but we're retrieving an array of items.
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Now, there's nothing to change here when we're adding items because, of course, self.default.set
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can take any object, right?
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Or at least theoretically.
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So let's see what happens when we try to run our app. Now, I'm ready hinting at what's going to come.
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But theoretically, at this point, we are creating a newItem using our class Item, we're setting its title
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property.
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The done property is set to false by default here. And then we're appending the item to itemArray, and
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then we're setting into our UserDefaults using the key "TodoListArray." And then when our app loads up,
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we use our UserDefaults to pull out an array. And if you remember, user defaults.array can be an
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array of any type, at least theoretically.
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And we're using the same key as we saved it and we're trying to pull it out as an array of items.
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So if that succeeds, then we set our itemArray to equal items.
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Let's go ahead and give our app a run and see what happens. So that's all working fine because we're
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initializing new items inside viewDidLoad and we're appending them to this itemArray.
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Now, the part that's interesting, because when we first press the add button and add a new item.
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So let's press the add button and let's add a new item.
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Now, once I hit add item, something dramatic happens
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and, of course, you can see we've got signals SIGABRT which doesn't say anything at all.
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But by now you should have seen it often enough
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if you're coding along because this means that our app has crashed. And if we scroll to the top of our
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debug console, as always, we'll find something that's trying to tell us why our app crashed.
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And the reason that it's telling us is attempting to set a non-property-list object using UserDefaults.
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So what does that mean?
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Well, did you remember how I said that UserDefaults is a property list?
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It has a whole bunch of key-value pairs.
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So, for example, you could have a key which is "TodoListArray" and the value is an array of strings.
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But in our case, we're trying to save an array of custom Item objects.
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Remember, our itemArray is an array of our own Item objects.
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and we're trying to save that into UserDefaults which it's rejecting, and it probably should reject,
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because by the time that you're trying to save an array of your custom objects, then you're probably
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misusing UserDefaults,
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so this is the extent where we can get to with the UserDefaults. And we have to start considering a
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slightly better solution than using UserDefaults to persist data which if you remember is only really
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intended for small pieces of data, and it's massively inefficient because it has to load up the entire
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plist before you can use or read any of the properties inside it.
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So we have to abandon ship and stop using UserDefaults.
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So I believe that it's always better to show rather than tell. And I can, of course, warn you don't use
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UserDefaults.
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It's not going to be very efficient and it's not going to work in lots of cases.
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But I think it's better to show you when we actually try to implement it and reach its limits.
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So remember, don't use UserDefaults for anything other than, basically, that right UserDefaults,
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so volume on, volume off, volume high, volume low. these kind of small tidbits. For bigger pieces of data
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and for saving data into databases, we've got better tools for them.
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So in the next lesson, we're going to be learning about one of those tools which is NSCoder.
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So I'll see you there.