adamahrens/getswifty

A Collection of Swift Learnings & Tutorials

GetSwifty

A Collection of Swift Learnings & Tutorials

Saving Data in iOS

Saving data in ios path from Ray Wenderlich

FileManager

Handles managing files for you. Each iOS app has it's own sandbox for storing files. FileManager is thread safe. Use the URL struct for dealing with files, directories, and paths.

A URL path is string. To add a file use .appendingPathComponent for the filename and use appendingPathExtension for the type of file it would be, such as .json or .txt.

You can use .lastPathComponent on a URL to get the filename with extension

JSON

Popular format for sending data over the web. Also viable for saving data on an iOS object. It only supports a few data types natively such as Bool, Integer, String, Array

Plist

Essentially like XML document. They always have a .plist extension. Saving a plist of similiar JSON information but will inherently require more space.

Networking with URLSession

Used to have to use NSURLConnection but Apple released in iOS 7 URLSession. Sits on top of Apple's networking stack.

Concurrency & DataTasks

Doing multiple things at once (log events, pull data, save to disk, etc). Path of execution is a Thread.

We could work directly with threads such as NSThread. Which can be harder. Another low level framework is GCD or Grand Central Dispatch. They use a FIFO order when executing work.

OperationQueue is another higher level framework built on top of GCD. It allows setting up depdencies and cancel operations easily.

Instead of just creating numerous Operation subclasses can just use closures with OperationQueue#addOperation or use the provided BlockOperation subclass that takes a closure in the init

Combine is the most recent which allows switching between threads with operations such as subscribeOn receive

The Main thread is not designed for concurrent threads to access it.

URLSessionConfiguration is used to configure how you want your URLSession to behave. Want it in privacy mode? Run on background threads? Store credentials?. It comes with a default, empheral is almost like incognito. It won't store cookies or cache to disk.

All configurations must be done before creating the URLSession. Updates after the fact do nothing.

In order to perform work you have to pass URLSessionTask to the URLSession these could be dataTask or downloadTask or uploadTask.

• DataTask response returned in memory
• UploadTask similar to datatask but easier to provide request body
• DownloadTask response is written to file. Useful for downloading images, audio, videos

You must call resume on all tasks since they start in a waiting state.

Downloading & Uploading

When downloading/uploading is crucial to understand priorities & cachce policies.

Priority suggestion helps determine how the OS should handle the request. If that data isn't important the system might not execute immediately. Priority goes from 0-1 with options such as defaultPriority, lowPriority: 0, and .highPriority: 1

Can also cache response to continually return it.

Both Download and Upload have delegate callbacks for details on task. Can use those to present progressViews or other detailed information.

NetworkLinkConditioner can be used to simulate your network speeds. Download from Apple Developer Tools

Network tasks provide the ability to cancel, pause, and resuming. When you pause store the provided Data to then pass to resume

Background Downloading & Websockets

Aside from the Data, Upload and Download tasks. We have two additional ones for WebSocket and Stream.

In order to support your app to download in the background. You need to configure your URLSessionConfig.networkServiceType to be of .background. You'll need to implement the delegate methods. iOS will eventually call an AppDelegate callback.

Websockets are used for two way connection/communication.

URLSession & Combine

Combine is a reactive framework. A Publisher emits events over time to all Subscribers that are listening for it.

Use compactMap to publish only non-nil. Great for when mapping data from the response to a decodable object

Use Publishers.zip when waiting for multiple requests to complete before updating the main thread with the data. Such as fetching an image and mp3 file.

Use flatMap to chain requests and establish dependencies

Combine has it's own error operators. Can also use the retry operator to allow calling a request again if it errors.

We can use tryMap and then throw our custom errors. Then we can mapError to our custom error enum

Authentication and Cookies

AppDelegate has receive authentication challenge if the method is implemented . Otherwise it can go to the URLSession challenge delegate method. It's of type URLAuthenticationChallenge

Application Transport Security for helping secure your connection to the server. Built in since El Capitan.

Cookies are automatically stored in the shared cookie store. Can get the HTTPCookie from the HTTPResponse

Use HTTPCookieStorage for deleting and storing cookies

ConcurrencyWithGCDAndOperations

ModernConcurrency

Task.isCancelled: Returns true if the task is still alive but has been canceled since the last suspension point. Task.currentPriority: Returns the current task’s priority. Task.cancel(): Attempts to cancel the task and its child tasks. Task.checkCancellation(): Throws a CancellationError if the task is canceled, making it easier to exit a throwing context. Task.yield(): Suspends the execution of the current task, giving the system a chance to cancel it automatically to execute some other task with higher priority.