/combine-workshop-swiftindia

Primary LanguageSwift

SwiftIndia Combine Workshop –– 08 Feb 2020

Agenda

Session 1: Quick intro to Combine, part 1

  • What is Combine
  • Building blocks of Combine
  • What is a Publisher
  • Different types of Publishers supported by Combine
  • What is a Subscriber
  • Different types of Subscribers supported by Combine
  • Lifecycle of publishers & subscribers
  • How to cancel a subscription

Session 2: Quick intro to Combine, part 2

  • What is an Operator
  • Different types of Operators supported by Combine

Session 3: How to make custom publishers & subscribers?

  • Publisher is a protocol
  • Wrapping UserDefaults into a publisher
  • Subscriber is a protocol
  • Wrapping UserDefaults into a subscriber

Session 4: Combine meets UIKit

  • Add TapPublisher in UIButton (UIControl in general)
  • Convert UIScrollViewDelegate into a Combine like API

Session 5: Error handling in Combine

  • What is Error in Combine
  • How to model custom Error
  • How does Error flow
  • How to react to errors
  • What is Fail publisher and how to use it
  • What are the operators used to transform and handle errors (Catch, TryCatch, MapError, ReplaceError, SetFailureType)

Session 6: Networking using Combine

  • Networking without Combine
  • Networkin with Combine
  • What is DataTaskPublisher
  • How to make an API request
  • How to handle response from server
  • How to parse success response
  • How to validate response to handle error
  • How to parse and handle error

Session 7: Handling multiple async tasks using Combine

  • Handling multiple async tasks without Combine (GCD & OperationQueue)
  • Combine operators that enable handling multiple async tasks
  • Merge
  • Zip
  • CombineLatest
  • Debounce

Session 8: Handling threads using Combine

  • Threading without Combine
  • Threading with Combine
  • SubscribeOn operator
  • ReceiveOn operator

Session 1: Quick intro to Combine, part 1

  • What is Combine

    • The Combine framework provides a declarative Swift API for processing values over time. These values can represent many kinds of asynchronous events.
    • Combine declares publishers to expose values that can change over time, and subscribers to receive those values from the publishers.
    • Customize handling of asynchronous events by combining event-processing operators.

  • Building blocks of Combine

    • Publisher
    • Subscriber
    • Operator

  • What is a Publisher

    • Declares that a type can transmit a sequence of values over time.
    • Source of values

  • Different types of Publishers supported by Combine

    • Just
    • Fail
    • Future
    • Deferred
    • DataTaskPublisher
    • NotificationCenter.Publisher
    • NSObject.KeyValueObservingPublisher
    • @Published
    • PassthroughSubject
    • CurrentValueSubject
    • AnyPublisher
    • many more...

  • What is a Subscriber

    • A Subscriber instance receives a stream of elements from a Publisher, along with life cycle events describing changes to their relationship.
    • Consumer of values

  • Different types of framework supported Subscribers

    • Sink
    • Assign
    • AnySubscriber

  • Lifecycle of publishers & subscribers

  • How to cancel a subscription
    • Cancellable
    • AnyCancellable

Session 2: Quick intro to Combine, part 2

  • What is an Operator

    • Operators are those publishers which can't generate value on their own but rather transform the value provided by a source publisher or a previous operator
    • They are used between a publisher and a subscriber
    • Roughly 3 kinds of operators
      • ones which modify the values
      • ones which modify the thread
      • ones which modify the stream itself

  • Different types of Operators supported by Combine

    • Map
    • FlatMap
    • Filter
    • Catch
    • MapError
    • Merge
    • Zip

Session 3: How to make custom publishers & subscribers?

  • Publisher is a protocol
public protocol Publisher {

    /// The kind of values published by this publisher.
    associatedtype Output

    /// The kind of errors this publisher might publish.
    associatedtype Failure : Error

    /// This function is called to attach the specified `Subscriber` to this `Publisher` by `subscribe(_:)`
    func receive<S>(subscriber: S) where S : Subscriber, Self.Failure == S.Failure, Self.Output == S.Input
}

// Self.Failure == S.Failure, Self.Output == S.Input

  • Wrapping UserDefaults into a publisher

  • Subscriber is a protocol

public protocol Subscriber : CustomCombineIdentifierConvertible {

    /// The kind of values this subscriber receives.
    associatedtype Input

    /// The kind of errors this subscriber might receive.
    associatedtype Failure : Error

    /// Tells the subscriber that it has successfully subscribed to the publisher and may request items.
    /// Use the received `Subscription` to request items from the publisher.
    func receive(subscription: Subscription)

    /// Tells the subscriber that the publisher has produced an element.
    func receive(_ input: Self.Input) -> Subscribers.Demand

    /// Tells the subscriber that the publisher has completed publishing, either normally or with an error.
    func receive(completion: Subscribers.Completion<Self.Failure>)
}
  • Wrapping UserDefaults into a subscriber

Session 4: Combine meets UIKit

  • Complete UIControl.Publisher

  • Convert UITableView's scrollViewDidScroll method into a Publisher

Session 5: Error handling in Combine

  • What is Error in Combine
    • Error is part of Publisher & Subscriber both
    • Any subscription can terminate in two ways, either via .finished or .failure(Error)
    • .failure(Error) is used to send errors
    • Just like value, we can also transform and observe errors
public protocol Publisher {

    /// The kind of errors this publisher might publish.
    /// Use `Never` if this `Publisher` does not publish errors.
    associatedtype Failure : Error
    ...
}

public protocol Subscriber {

    /// The kind of errors this subscriber might receive.
    /// Use `Never` if this `Subscriber` cannot receive errors.
    associatedtype Failure : Error
    ...
}

extension Subscribers {
    /// - finished: The publisher finished normally.
    /// - failure: The publisher stopped publishing due to the indicated error.
    public enum Completion<Failure> where Failure : Error {
	
        case finished
        case failure(Failure)
    }
}

  • How to model custom Error

  • How does Error flow

  • How to react to errors

  • A note about Never

/// Use `Never` as the return type when declaring a closure, function, or
/// method that unconditionally throws an error, traps, or otherwise does
/// not terminate.
///
///     func crashAndBurn() -> Never {
///         fatalError("Something very, very bad happened")
///     }

public enum Never {}

Session 6: Networking using Combine

  • Networking without Combine
  • Networkin with Combine
  • What is DataTaskPublisher
  • How to make an API request
  • How to handle response from server
  • How to parse success response
  • How to validate response to handle error
  • How to parse and handle error

Session 7: Handling multiple async tasks using Combine

  • Handling multiple async tasks without Combine (GCD & OperationQueue)
  • Combine operators that enable handling multiple async tasks
    • Merge
    • Zip
    • CombineLatest
    • Debounce

Session 8: Handling threads using Combine

  • Threading without Combine
  • Threading with Combine
  • SubscribeOn operator
  • ReceiveOn operator