[MUSIC] >> So this is Raif Brockhaus again, so we are working on writing the iOS application and I'm doing the second part here right now. So in the first part of the application we wrote a sample application which allows us to create a shopping list, it's a simple iPhone application. In the interface, interface builder with auto-layout features and we created an array for list some items to represents the model, right? So we created a dedicated model class. And we were then able to have the ViewController handle the logic so that when we entered values. The data would be entered into the model and the list view would re-draw the model, right? So the one part which is standing out or missing still is the ability to write the file of the data into the file system. All right and so a couple of things need to happen for that right now. So I go back into the Xcode environment for that. And I have my application project open here. And so what I need to do is I need to write a couple of functions. So I explained already that the iPhone application is running in a sand box. Right? So every single mobile application on the iPhone has its own sand box. Has its own dedicated area where data can be stored. Right? And so we want to access a file in that sand box. Right? So we need to get access to a list of directories that exists on the phone. And then inside there we need to get actually the access to a path to a file where we want to store our data. To do that we actually take our model class which is our ShoppingList here. And inside our ShoppingList we add a couple of additional data items. So first thing which we do is we create a private variable. Right, and so, a constant and file URL of type NSURL, URL. So we have an NSURL and this NSURL we need to initialize for something, right? So, what we do here is, inside that code actually, we let our document's directory URLs = to the NFS file. NSFileManager. So we take the FileManager, we get the defaultManager. From the defaultManager we looked at the URLs for directory, and now we want the various directories on the phone. And for the directory which we want to have, is. Sorry for the little interruption there. One second. Send query to. So let document directory URLs be equal to NSFileManager. If we take the default file manager from the default file manager we take the URLs for the directory. There we use the document directory and inside the domains we use the, not this one, but we use the user domain's mask. So all the ones for the user domain mask. Then the next thing which we need to do, so this is basically giving us the list of directory URLs, right? So then we say let the document directory URL which we want to use be a URL by Be the URLs dot first so we take the first URL. And then what we want to return is the documentary URL. And from that URL we want to URL by append. All right, so the past component. And we just call this shopping list here. Items. So we are writing out the items. So we still have one defect there. Okay, so just to recap very quickly, so we get the document directory URLs by asking the file manager to give us a default file manager. From the default file manager we get the URLs from the directories. The ones we want are the document directory. Document. The directory and in the domains for user domain mask. And then we take one specific directory URL and that one is from the directories that will receive the first one. And then the last thing which we need to do is we take that URL and append the word shopping list. And that should actually bring us to the URL. The second thing which we need to do is we write a function save items and we want a function to load the items, all right? So the function to save the items. So we let our items array be items as NSArray. So why do we do that? Right, so again we have a cast here and we take our items array, the regular array and cast it into an NSArray. And the reason why we do that is we want to call a specific function which is only available on the NSArray. And we want to use that function actually to write the area to a URL. So for that we need a little bit of Objective-C code apparently. And so the first thing that we need to do for that is we ask if Items Arrary.writetofile and then the path which we pass in as the fileURL. And equality bool true. Then we say print Was not able to save shopping list, right? So what we do here is we look at the items array, and write it to the file, the file URL. Private file URL. And it complains, cannot convert the value to expected argument of type string. File URL right here Okay, there's a little typo here. I found the typo. ToURL. And so that's the file URL automatically is true. Cut this out, and so that code now compiles and then the next part which we need to do is we need to write one function to actually load the data. So the first part, which we do here, is function load Items and in the load items if that item's array. Is equal and NSarray. ContentsofURL. That's where we need to be careful, contentsofURL, fileURL. S area of strings. The string array. I'll explain everything in a second. Then items equal items array. So, the two things which are happening here is. So the save items function takes an item array. And actually it moves or it casts it into an NS array. And then the next part what it does is it checks if it can write to file. The file URL we passed in is here from our private member which is a constant now. And so then we write all the data, the array, in automatically pieces into that file. And if we can't do that, if this gives us an error, then we basically just show we are not able to save the shopping list. For the reading, we do the opposite. So if we let an items array, it's an NS array. For the NSArray, we look at the contents of a URL, so we pass in a URL, and so this is what the reason why we needed an NSArray, right? We needed to be able to go and load in the contents of the URL. If that works, then we pass it as a string and assign it to the items array. And then we say all items is all items already. And so now, we need to do a couple more small things. So the one thing is we need to write an init function. I know we don't have an init function in our code anymore, because if we don't do anything specific then we don't have any need to write an init function. But here right now so we call an override for the initalizer for our shopping list class, and what we do here is we call super.init. So first thing right we always need to call because we inherit from NSobject, right? We always need to make sure that we call the initializer for the NSobject. After we initialize that one the next thing which we just do is load items. So with other words, whenever the application goes and initializes an object of the shopping list, first thing the shopping list does. Is actually looks into the file system and checks if we have already a shopping cart list saved, and it just loads it into memory. So that's one item which we need to do. The other item which we need to do is when we add an item. So when we add an item we need to now say append an item and then each time when we added an item into our shopping list, we just go and save the items. So we call the function to save the items back into the list. So the next thing we need to do is we just run the application. Show you a few tricks there. So, when the application runs now, I have my user interface here. And, the first thing I do is I add milk to my shopping list. I insert the milk and then I add butter. So the next thing which I do now is I actually stop the application .and I set a break point here in node items. So when I run the application it actually hits the break point for the load items. Right? So I continue on the break point, and you see when the application launches, then it actually loads the data from memory. So to recap, in the summary, so we wrote this little shopping list, and you can use that code for anything, right. You can store geo-coordinates, you can shopping lists. You can do a to do list, item list, any kind of lists. You get the data. Then we take the data and move the data into a list view. So we use a list view controller to display the data. Now, there's a lot of features of the list view which I didn't show you. For example, custom table cells, so you can do a lot of things to improve the user interface. You can create ability to switch the roles, sort the list view, various other capabilities. So if anybody is very interested in that, please expand the functionality in your code for that. And then the next part is we save the data, we persist the data in the file system. Now, when we persist the data in the file system, that makes it actually a usable application, right? So could technically already start using it for something. But in the other modules which are following now, we will also show you actually how to make calls to the server and persist data on the server. Which happens in many cases so that you are able to say, for example, I have a shopping list, I saved something on the phone. Doesn't help you if you also have an iPad, right? So you will be able then persist something on the server, and then write, for example, code to share the shopping list with your spouse, right? So all the basics of that, we have in this application. And the rest we'll show you in the remaining modules. Hope you enjoyed the session. >> [MUSIC]
