You can extract a dictionary value by key or an array value by index using type cast optional binding with subscript accessors or pattern matching with enumeration.
A Restaurant has a name of type String , a location expressed as a coordinate pair, and a Set of meals containing values of a nested Meal enumeration. To convert from a JSON representation to a Restaurant object, write an initializer that takes an Any argument that extracts and transforms data from the JSON representation into properties.
If your app communicates with one or more web services that do not return a single, consistent representation of a model object, consider implementing several initializers to handle each of the possible representations.
In the example above, each of the values are extracted into constants from the passed JSON dictionary using optional binding and the as? For the name property, the extracted name value is simply assigned as-is. For the coordinate property, the extracted latitude and longitude values are combined into a tuple before assignment. Session Types 2. File Download when app is in background. Default session: The shared session uses the global singleton credential, cache and cookie storage objects.
Ephemeral session An ephemeral session has no persistent disk storage for cookies,cache or credentials, they are stored in RAM and purged automatically when the session is invalided. Background session Background session is similar to Default session, But it can be used to perform networking operations on behalf of a suspended application, within certain constraints. Tasks are created in two ways. It's important to know when to work with the file system on the background thread.
Apple says that "because file operations involve accessing the disk, performing those operations asynchronously is almost always preferred. Grand Central Dispatch is the best way to work with Disk asynchronously. Here's an example:. Don't forget to handle these sorts of tasks being interrupted. This information allows us to gauge when it's appropriate to store data on the user's disk. Note: These variables return Optional Int s since retrieving file system resource values may fail and return nil.
However this is very unlikely to happen, and this behavior exists solely for safety purposes. You should generally never use the. Most of these helper methods have URL counterparts, in case you want to work with files directly with their file system URLs.
Disk is thorough , meaning that it will not leave an error to chance. Almost all of Disk's methods throw errors either on behalf of Foundation or custom Disk Errors that are worth bringing to your attention.
These errors have a lot of information, such as a description, failure reason, and recovery suggestion:. The example above takes care of the most common error when dealing with the file system: removing a file that doesn't exist. Nothing really fit the bill except NSKeyedArchiver , but there were too many hoops to jump through.
Working with network responses' JSON data and converting them to usable structures has never been easier. Disk aims to extend that simplicity of working with data to the file system. You send a URL request to a server, asking it for some data.
You hope the server returns the data quickly, but you don't know how long it will take. Instead of making your user wait patiently for the server to give you the data, you use a completion handler. This means you can tell your app to go off and do other things, such as loading the rest of the page. You tell the completion handler to tap your app on the shoulder once it has the information you want. You can specify what that information is.
That way, when your app gets tapped on the shoulder, it can take the information from the completion handler and do something with it. Usually what you'll do is reload the table view so the data appears to the user.
Here's an example of what a completion handler looks like. The first example is setting up the API call itself:. URLSession is like the manager of a team. The manager doesn't do anything on her own. Her job is to share the work with the people in her team, and they'll get the job done.
Her team are dataTasks. Every time you need some data, write to the boss and use URLSession. You can give the dataTask different types of information to help you achieve your goal. Giving information to dataTask is called initialization. I initialism my dataTasks with URLs. Here's an example:. You can give these data types different names, like data, res, err or someData, someResponse, someError. For the sake of convention, it's best to stick to something obvious rather than go rogue with new variable names.
Let's start with error. If the dataTask returns an error , you'll want to know that upfront. It means you can direct your code to handle the error gracefully. It also means you won't bother trying to read the data and do something with it as there is an error in returning the data. Below I am handling the error really simply by printing an error to the console and exiting the function.
There are many other ways you could handle the error if you wanted to. Think about how fundamental this data is to your app. For example, if you have a banking app and this API call shows users their balance, then you may want to handle the error by presenting a modal to the user that says, "Sorry, we're experiencing a problem right now.
Please try again later. Next we look at the response. You can cast the response to be an httpResponse. That way you can look at the status codes and make some decisions based on the code.
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