Shift

Light-weight EventKit wrapper.

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Shift is a light-weight concurrency wrapper for EventKit:

• Concurrency ready with async/await. (tag: 0.7.0)
• Tranditional, Result completion handler if preferred (tag: 0.6.0)
• Thread-safe.
• SwiftUI supported.

Shift is currently being used by Clendar app.

Requirement

• iOS 15.0 for async/await, tag 0.7.0
• iOS 14.0 and below for Result-based, tag <0.6.0
• Swift version 5.5
• Xcode 13.1

Install

This component is built using Swift Package Manager, it is pretty straight forward to use:

1. In Xcode (11+), open your project and navigate to File > Swift Packages > Add Package Dependency…
2. Paste the repository URL (https://github.com/vinhnx/Shift) and click Next.
3. For Rules, select Version, in here, you can choose either:

• Async/await => tag 0.7.0
• Result-based completion handler => tag 0.6.0

5. Click Finish to resolve package into your Xcode project.

Tag Version:

Concurrency support is now ready, in tag 0.7.0

In order to use old Result-based completion hanlders, please use tag 0.6.0.

Getting Started

First thing first:

• Add Calendar usage description to your app’s Info.plist to request for user’s Calendars access.

<key>NSCalendarsUsageDescription</key>
    <string>&quot;$(PRODUCT_NAME) needs your permission to create events&quot;</string>

• (Optional) configure own calendar name to request access to, preferrable in AppDelegate‘s didFinishLaunchingWithOptions (Swift) or App‘s init() (SwiftUI):

Swift AppDelegate:

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        Shift.configureWithAppName("MyApp")
        return true
    }
}

in SwiftUI App, first import Shift, then configure your app’s name to differntiate the name of your app’s calendar in system’s EventKit.

import SwiftUI
import Shift

@main
struct MyApp: App {
    init() {
        Shift.configureWithAppName("MyApp")
    }

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

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A quick NOTE about concurrency

Since async functions can only be called on concurrency context, if you call async function inside synchornouse context, Xcode will throws an error:

So, there are two ways to awaiting for concurrency result, base on context:

• Inside async function

  func doSomethingAsync() async {
    // ... other works
    let events = try? await Shift.shared.fetchEvents(for: Date())
    // ... other works
  }

• Inside Task closure:

  func regularFunction() {
    // ... other works
  
    Task {
        let events = try? await Shift.shared.fetchEvents(for: Date())
        // then...
    }
  
    // ... other works
  }

Either is fine, base on caller’s context.

You can read more about Task here https://developer.apple.com/documentation/swift/task.

In SwiftUI views, you can call async functions inside View’ .task modifier:

import EventKit
import SwiftUI
import Shift

struct ContentView: View {
    @StateObject var eventKitWrapper = Shift.shared
    @State private var selectedEvent: EKEvent?

    var body: some View {
        LazyVStack(alignment: .leading, spacing: 10) {
            ForEach(eventKitWrapper.events, id: \.self) { event in
                Text(event: event)
            }
        }
        .padding()
        .task { // wrap async call inside .task modifier
            try? await eventKitWrapper.fetchEventsForToday() 
        }
    }
}

You can read more about SwiftUI’s .task modifier here https://developer.apple.com/documentation/swiftui/view/task(priority:_:).

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Usage Example

Fetch list of events for a particular date:

async/await (NEW)

inside regular async function:

func fetchEvents() async {
    do {
        let events = try await Shift.shared.fetchEvents(for: Date()) // await for events fetching
    } catch {
        print(error) // handle error
    }
}

or standalone:

Task {
    let events = try? await Shift.shared.fetchEvents(for: Date()) // await for events fetching
}

Result-based completion handlers (old pattern, but still doable if you preferred this to async/await)

Shift.shared.fetchEvents(for: Date()) { result in
    switch result {
    case let .success(events): print(events) // got events
    case let .failure(error): print(error) // handle error
    }
}

Shift.shared.fetchEventsRangeUntilEndOfDay(from: Date()) { result in
    switch result {
    case let .success(events): print(events) // got events
    case let .failure(error): print(error) // handle error
    }
}

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Create Event:

async/await

inside regular async function:

func myAsyncFunction() async {
    try? await Shift.shared.createEvent("Be happy!", startDate: startTime, endDate: endTime)
}

or standalone:

Task {
    try? await Shift.shared.createEvent("Be happy!", startDate: startTime, endDate: endTime)
}

Result

Shift.shared.createEvent("Be happy!", startDate: startTime, endDate: endTime) { result in
    switch result {
    case let .success(event): print(event) // created event
    case let .failure(error): print(error) // handle error
    }
}

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Delete event:

async/await

inside regular async function:

func myAsyncFunction() async {
    try? await Shift.shared.deleteEvent(identifier: eventID)
}

or standalone:

Task {
    try? await Shift.shared.deleteEvent(identifier: eventID)
}

Result

Shift.shared.deleteEvent(identifier: eventID) { result in
    switch result {
    case let .success: print("done!") // deleted event
    case let .failure(error): print(error) // handle error
    }
}

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SwiftUI Example

Shift is conformed ObservableObject with an @Published events property, so it’s straight-forward to use in SwiftUI binding mechanism.

Result-based example:

import EventKit
import SwiftUI
import Shift

struct ContentView: View {
    @StateObject var eventKitWrapper = Shift.shared
    @State private var selectedEvent: EKEvent?

    var body: some View {
        LazyVStack(alignment: .leading, spacing: 10) {
            ForEach(eventKitWrapper.events, id: \.self) { event in
                Text(event: event)
            }
        }
        .padding()
        .onAppear {
            eventKitWrapper.fetchEventsForToday()
        }
    }
}

async/await example:

import EventKit
import SwiftUI
import Shift

struct ContentView: View {
    @StateObject var eventKitWrapper = Shift.shared
    @State private var selectedEvent: EKEvent?

    var body: some View {
        LazyVStack(alignment: .leading, spacing: 10) {
            ForEach(eventKitWrapper.events, id: \.self) { event in
                Text(event: event)
            }
        }
        .padding()
        .task {
            try? await eventKitWrapper.fetchEventsForToday() 
        }
    }
}

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Apps currently using Shift

• Clendar - Clendar - universal calendar app. Written in SwiftUI. Available on App Store. MIT License.

(add yours here)

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Help, feedback or suggestions?

Feel free to open an issue or contact me on Twitter for discussions, news & announcements & other projects. 🚀

I hope you like it! :)