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Flint is a framework for building apps for Apple platforms out of Features and Actions using the power of Swift.

Your app’s Features are enabled based on runtime constraints; system permissions, OS version or in-app purchases. It takes your Actions and provides enhanced logging, automatic analytics events, NSUserActivity integration for Handoff, Search and Siri prediction, URL handling, Siri Shortcuts support, user activity timelines for debugging and much more.

It uses coding conventions much like web application development frameworks like Rails. However it uses the static compilation and associated type features of Swift to provide enhanced safety and code completion.

The result is apps that are more robust and more polished, with less boilerplate and better decoupling without requiring a massive architectural shift or specific UI/model approach.

We made Flint because we want people to build great apps for Apple platforms that make the most of native platform capabilities with less hassle.

🏠 flint.tools is the official web site, with guide & API docs and blog

💬 Get help on the FlintCore Slack

✉️ Subscribe to the Flint newsletter

🐦 Follow @flintframework on Twitter

📖 View the documentation or help us improve it with a pull request

🔬 View the FlintDemo-iOS sample project

🎧 Listen to the iDeveloper podcast interview where project lead Marc Palmer explains the motivation and ideas behind Flint

The basics

Features are what your app can do. Features in Flint conform to the Feature protocol:

import FlintCore

class DocumentManagementFeature: Feature {
    static let description = "Create, Open and Save documents"

    static let openDocument = action(DocumentOpenAction.self)

    static func prepare(actions: FeatureActionsBuilder) {
        actions.declare(openDocument)
    }
 }

They typically have one or more actions, and some have sub-features.

Actions are what your users can do with your features, like Open a document, Close a document, Share a document. Actions are types conforming to Action that are then declared on features as in the above example, taking an input and a presenter that are types you define:

import FlintCore

final class DocumentOpenAction: Action {
    typealias InputType = DocumentRef
    typealias PresenterType = DocumentPresenter

    static var description = "Open a document"

    static func perform(context: ActionContext<DocumentRef>,
                        presenter: DocumentPresenter,
                        completion: Completion) -> Completion.Status {
        presenter.openDocument(context.input)
        return completion.completedSync(.success)
    }
}

Once you define actions, Flint can observe when your app performs them. This unlocks many behaviours like automatic NSUserActivity and Siri integration, analytics tracking and improved debug logging.

However, because Flint can also knows how to invoke your actions for a given input, it can handle all the different app entry points for you too, including app or deep-linking URLs and continued activities including Handoff, Spotlight, Siri Suggestions. Read more in the Features & Actions guide.

What about features that require in-app purchases or certain system permissions? Conditional Features support constraints. These can include platforms, OS versions, system permissions, in-app purchases and more. Thanks to Swift your code can’t perform actions of conditional features unless you also handle the case where the feature is not currently available.

import FlintCore

let premiumSubscription = AutoRenewingSubscriptionProduct(name: "💎 Premium Subscription",
                                                          description: "Unlock the Selfietron!",
                                                          productID: "SUB0001")

public class SelfieFeature: ConditionalFeature {
    public static var description: String = "Selfie Posting"

    public static func constraints(requirements: FeatureConstraintsBuilder) {
      // Allow the user to turn this on/off themselves
      requirements.userToggled(defaultValue: true)

      // Require isEnabled to return `true` at runtime
      requirements.runtimeEnabled()

      // Require a purchase for this feature to be enabled
      requirements.purchase(premiumSubscription)

      // Require these permissions before the feature's actions can be used
      requirements.permissions(.camera,
                               .photos,
                               .location(usage: .whenInUse))
    }

    ...
}

Features that require multiple permissions or one of many purchase options are easily accommodated, and Flint will help you build a first class permissions onboarding UI to maximise the number of users that can use your feature.

When you need to perform an action from a conditional feature, you are forced to first check if the feature is available and handle the case where it is not:

if let request = DocumentSharingFeature.share.request() {
    request.perform(withInput: document, presenter: presenter)
} else {
    showPremiumUpgradeOrPermissionAuthorisations()
}

This makes your code cleaner and safer. Everybody on the team can see which code is internally feature-flagged or requires a purchase, and which permissions your app requires.

See the programming guide for Conditional Features for more details.

Handling URLs

To handle incoming URLs all you need to do is define an action – a type that conforms to the Action protocol, and add it to a Feature that has one or more URL routes for the action.

Consider the common case of handling a user sign-up confirmation link sent by e-mail. The URL will contain a token and the app should open when it is tapped, verify the token and then show the You signed in! screen.

import FlintCore

class UserAccountManagementFeature: Feature, URLMapped {
    static let description = "User sign-up, sign in and sign out"

    static let confirmAccount = action(ConfirmAccountAction.self)

    static func prepare(actions: FeatureActionsBuilder) {
        actions.declare(confirmAccount)
    }

    // 💥 Use `routes` to define the URLs and actions
    static func urlMappings(routes: URLMappingsBuilder) {
        routes.send("account/confirm", to: confirmAccount)
    }
}

Once you add the custom URL scheme to your Info.plist and/or an associated domain to your entitlements, your app would then invoke the confirm account action when it is asked to open URLs like:

  • your-app://account/confirm
  • https://yourappdomain.com/account/confirm

There’s support for multiple mappings per action, multiple URL schemes and multiple associated domains, so legacy URLs are no problem. There’s a little glue code to add to your app delegate and to set up your UI when the action comes in.

The action type ConfirmAccountAction is not shown here, for brevity. See the Features and Actions guide for full details.

Of course you can easily perform this same action from code in your app if required:

UserAccountManagementFeature.confirmAccount.perform(withInput: confirmationToken, presenter: presenter)

If you need to, you can create URLs that link to these mapped actions using Flint.linkCreator.

See the programming guide for Routes for more details.

Automatic Handoff and Siri Suggestions support

Apple’s NSUserActivity is used extensively for telling the system what the user is currently doing, to integrate Handoff between devices Siri app suggestions, some Spotlight Search integration as well as deep linking. All too often people don’t implement this, because of the challenges of executing arbitrary actions in your app when the user chooses an activity.

Flint can do this automatically for you, with zero effort if your Action also supports URL routes.

import FlintCore

final class DocumentOpenAction: Action {
    typealias InputType = DocumentRef
    typealias PresenterType = DocumentPresenter

    static var description = "Open a document"

    // 💥 Just tell Flint what activity types to use
    static var activityEligibility: Set<ActivityEligibility> = [.perform, .handoff]

    static func perform(context: ActionContext<DocumentRef>,
                        presenter: DocumentPresenter, 
                        completion: Complettion) -> Completion.Status {
        // … do the work
    }
}

This is all you have to do, aside from add NSUserActivityTypes to your Info.plist and list the activity IDs automatically generated by Flint.

You can of course customise the attributes of the NSUserActivity if you want to, by defining a prepare(activity:for:) function. See the Activities guide.

See the programming guide for Activities for more details.

Track analytics events when users do things

Most apps end up having to do some kind of analytics reporting to get an idea of what your users are actually doing. An analytics event is typically an event ID and a dictionary of keys and values. Flint makes emitting these easy and consistent, using any analytics service you want. Even your own home-spun backend.

So when your marketing people say they want their analytics reporting system to show them when people open documents, you simply set the analyticsID property on the action, and Flint’s AnalyticsReporting component will automatically pick it up whenever that action is performed, passing it to your analytics provider.

import FlintCore

final class DocumentOpenAction: Action {
    typealias InputType = DocumentRef
    typealias PresenterType = DocumentPresenter

    static let description = "Open a document"

    // 💥 Enable analytics with just one property!
    static let analyticsID = "user-open-document"

    static func perform(context: ActionContext<DocumentRef>, 
                        presenter: DocumentPresenter, 
                        completion: Completion) -> Completion.Status {
        // … do the work
    }
}

Of course you can customise the dictionary of data passed to the Analytics provider by defining an analyticsAttributes() function.

See the programming guide for Analytics for more details.

Getting started

Flint supports Carthage and Cocoapods. See the Getting Started guide

Find out more

All this is just the tip of the iceberg. Flint has much more to offer and through the use of protocols almost everywhere, has many extension and customisation points so that you aren’t locked in to anything like a specific analytics provider.

If you want to see a sample project that uses Flint, there is the FlintDemo-iOS project here on Github. You can browse that to get an idea of how a real app might use Flint.

View all the documentation

Philosophy

We are all-in on Swift but we don’t want to be smartypants who can’t read our own code weeks later. We take a few advanced Swift geatures that make great things possible: Protocol Oriented Programming, some generics and a very small amount of associated types.

We deliberately avoid the more oblique patterns because we want this framework to be very accessible and easy for everybody to reason about, irrespective of the paradigm they have chosen for their codebase.

Community and Contributing

We have a community Slack you can join to get help and discuss ideas. Join at flintcore.slack.com.

We would love your contributions. Please raise Issues here in Github and discuss your problems and suggestions. We look forward to your ideas and pull requests.

Flint is copyright Montana Floss Co. with an MIT open source licence.