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Turbolinks for iOS

⚠️ Note: this repo is no longer being maintained. We recommend migrating to Turbo iOS which supports both Turbo 7 and Turbolinks 5 apps. Follow the migration guide to update from this framework to Turbo. ⚠️

Build high-fidelity hybrid apps with native navigation and a single shared web view. Turbolinks for iOS provides the tooling to wrap your Turbolinks 5-enabled web app in a native iOS shell. It manages a single WKWebView instance across multiple view controllers, giving you native navigation UI with all the client-side performance benefits of Turbolinks.

Features

• Deliver fast, efficient hybrid apps. Avoid reloading JavaScript and CSS. Save memory by sharing one WKWebView.
• Reuse mobile web views across platforms. Create your views once, on the server, in HTML. Deploy them to iOS, Android, and mobile browsers simultaneously. Ship new features without waiting on App Store approval.
• Enhance web views with native UI. Navigate web views using native patterns. Augment web UI with native controls.
• Produce large apps with small teams. Achieve baseline HTML coverage for free. Upgrade to native views as needed.

Requirements

Turbolinks for iOS is written in Swift 5.0 and requires Xcode 10.2. It should also work with Swift 4.2 as well. It currently supports iOS 10 or higher, but we'll be dropping iOS 10 support in the next version.

Web views are backed by WKWebView for full-speed JavaScript performance.

Note: You should understand how Turbolinks works with web applications in the browser before attempting to use Turbolinks for iOS. See the Turbolinks 5 documentation for details.

Installation

Install Turbolinks manually by building Turbolinks.framework and linking it to your project.

Installing with Carthage

Add the following to your Cartfile:

github "turbolinks/turbolinks-ios" "master"

Installing with CocoaPods

Add the following to your Podfile:

use_frameworks!
pod 'Turbolinks', :git => 'https://github.com/turbolinks/turbolinks-ios.git'

Then run pod install.

Running the Demo

This repository includes a demo application to show off features of the framework. The demo bundles a simple HTTP server that serves a Turbolinks 5 web app on localhost at port 9292.

To run the demo, clone this repository to your computer and change into its directory. Then, start the demo server by running TurbolinksDemo/demo-server from the command line.

Once you’ve started the demo server, explore the demo application in the Simulator by opening turbolinks-ios.xcworkspace and running the TurbolinksDemo target.

Getting Started

We recommend playing with the demo app to get familiar with the framework. When you’re ready to start your own application, see our Quick Start Guide for step-by-step instructions to lay the foundation.

Understanding Turbolinks Concepts

The Session class is the central coordinator in a Turbolinks for iOS application. It creates and manages a single WKWebView instance, and lets its delegate—your application—choose how to handle link taps, present view controllers, and deal with network errors.

A Visitable is a UIViewController that can be visited by the Session. Each Visitable view controller provides a VisitableView instance, which acts as a container for the Session’s shared WKWebView. The VisitableView has a pull-to-refresh control and an activity indicator. It also displays a screenshot of its contents when the web view moves to another VisitableView.

When you tap a Turbolinks-enabled link in the web view, the Session asks your application how to handle the link’s URL. Most of the time, your application will visit the URL by creating and presenting a Visitable. But it might also choose to present a native view controller for the URL, or to ignore the URL entirely.

Creating a Session

To create a Session, first create a WKWebViewConfiguration and configure it as needed (see Customizing the Web View Configuration for details). Then pass this configuration to the Session initializer and set the delegate property on the returned instance.

The Session’s delegate must implement the following two methods.

func session(session: Session, didProposeVisitToURL URL: NSURL, withAction action: Action)

Turbolinks for iOS calls the session:didProposeVisitToURL:withAction: method before every application visit, such as when you tap a Turbolinks-enabled link or call Turbolinks.visit(...) in your web application. Implement this method to choose how to handle the specified URL and action.

See Responding to Visit Proposals for more details.

func session(session: Session, didFailRequestForVisitable visitable: Visitable, withError error: NSError)

Turbolinks calls session:didFailRequestForVisitable:withError: when a visit’s network request fails. Use this method to respond to the error by displaying an appropriate message, or by requesting authentication credentials in the case of an authorization failure.

See Handling Failed Requests for more details.

Working with Visitables

Visitable view controllers must conform to the Visitable protocol by implementing the following three properties:

protocol Visitable {
    weak var visitableDelegate: VisitableDelegate? { get set }
    var visitableView: VisitableView! { get }
    var visitableURL: NSURL! { get }
}

Turbolinks for iOS provides a VisitableViewController class that implements the Visitable protocol for you. This view controller displays the VisitableView as its single subview.

Most applications will want to subclass VisitableViewController to customize its layout or add additional views. For example, the bundled demo application has a DemoViewController subclass that can display a custom error view in place of the VisitableView.

If your application’s design prevents you from subclassing VisitableViewController, you can implement the Visitable protocol yourself. See the VisitableViewController implementation for details.

Note that custom Visitable view controllers must forward their viewWillAppear and viewDidAppear methods to the Visitable delegate’s visitableViewWillAppear and visitableViewDidAppear methods. The Session uses these hooks to know when it should move the WKWebView from one VisitableView to another.

Building Your Turbolinks Application

Initiating a Visit

To visit a URL with Turbolinks, first instantiate a Visitable view controller. Then present the view controller and pass it to the Session’s visit method.

For example, to create, display, and visit Turbolinks’ built-in VisitableViewController in a UINavigationController-based application, you might write:

let visitable = VisitableViewController()
visitable.URL = NSURL(string: "http://localhost:9292/")!

navigationController.pushViewController(visitable, animated: true)
session.visit(visitable)

Responding to Visit Proposals

When you tap a Turbolinks-enabled link, the link’s URL and action make their way from the web view to the Session as a proposed visit. Your Session’s delegate must implement the session:didProposeVisitToURL:withAction: method to choose how to act on each proposal.

Normally you’ll respond to a visit proposal by simply initiating a visit and loading the URL with Turbolinks. See Initiating a Visit for more details.

You can also choose to intercept the proposed visit and display a native view controller instead. This lets you transparently upgrade pages to native views on a per-URL basis. See the demo application for an example.

Implementing Visit Actions

Each proposed visit has an Action, which tells you how you should present the Visitable.

The default Action is .Advance. In most cases you’ll respond to an advance visit by pushing a Visitable view controller for the URL onto the navigation stack.

When you follow a link annotated with data-turbolinks-action="replace", the proposed Action will be .Replace. Usually you’ll want to handle a replace visit by popping the topmost view controller from the navigation stack and pushing a new Visitable for the proposed URL without animation.

Handling Form Submission

By default, Turbolinks for iOS prevents standard HTML form submissions. This is because a form submission often results in redirection to a different URL, which means the Visitable view controller’s URL would change in place.

Instead, we recommend submitting forms with JavaScript using XMLHttpRequest, and using the response to tell Turbolinks where to navigate afterwards. See Redirecting After a Form Submission in the Turbolinks documentation for more details.

Handling Failed Requests

Turbolinks for iOS calls the session:didFailRequestForVisitable:withError: method when a visit request fails. This might be because of a network error, or because the server returned an HTTP 4xx or 5xx status code.

The NSError object provides details about the error. Access its code property to see why the request failed.

An error code of .HTTPFailure indicates that the server returned an HTTP error. You can access the HTTP status code in the error object's userInfo dictionary under the key "statusCode".

An error code of .NetworkFailure indicates a problem with the network connection: the connection may be offline, the server may be unavailable, or the request may have timed out without receiving a response.

func session(session: Session, didFailRequestForVisitable visitable: Visitable, withError error: NSError) {
    guard let errorCode = ErrorCode(rawValue: error.code) else { return }

    switch errorCode {
    case .HTTPFailure:
        let statusCode = error.userInfo["statusCode"] as! Int
        // Display or handle the HTTP error code
    case .NetworkFailure:
        // Display the network failure or retry the visit
    }
}

HTTP error codes are a good way for the server to communicate specific requirements to your Turbolinks application. For example, you might use a 401 Unauthorized response as a signal to prompt the user for authentication.

See the demo app’s ApplicationController for a detailed example of how to present error messages and perform authorization.

Setting Visitable Titles

By default, Turbolinks for iOS sets your Visitable view controller’s title property to the page’s <title>.

If you want to customize the title or pull it from another element on the page, you can implement the visitableDidRender method on your Visitable:

func visitableDidRender() {
    title = formatTitle(visitableView.webView?.title)
}

func formatTitle(title: String) -> String {
    // ...
}

Starting and Stopping the Global Network Activity Indicator

Implement the optional sessionDidStartRequest: and sessionDidFinishRequest: methods in your application’s Session delegate to show the global network activity indicator in the status bar while Turbolinks issues network requests.

func sessionDidStartRequest(_ session: Session) {
    UIApplication.shared.isNetworkActivityIndicatorVisible = true
}

func sessionDidFinishRequest(_ session: Session) {
    UIApplication.shared.isNetworkActivityIndicatorVisible = false
}

Note that the network activity indicator is a shared resource, so your application will need to perform its own reference counting if other background operations update the indicator state.

Changing How Turbolinks Opens External URLs

By default, Turbolinks for iOS opens external URLs in Safari. You can change this behavior by implementing the Session delegate’s optional session:openExternalURL: method.

For example, to open external URLs in an in-app SFSafariViewController, you might write:

import SafariServices

// ...

func session(session: Session, openExternalURL URL: NSURL) {
    let safariViewController = SFSafariViewController(URL: URL)
    presentViewController(safariViewController, animated: true, completion: nil)
}

Becoming the Web View’s Navigation Delegate

Your application may require precise control over the web view’s navigation policy. If so, you can assign yourself as the WKWebView’s navigationDelegate and implement the webView:decidePolicyForNavigationAction:decisionHandler: method.

To assign the web view’s navigationDelegate property, implement the Session delegate’s optional sessionDidLoadWebView: method. Turbolinks calls this method after every “cold boot,” such as on the initial page load and after pulling to refresh the page.

func sessionDidLoadWebView(_ session: Session) {
    session.webView.navigationDelegate = self
}

func webView(webView: WKWebView, decidePolicyForNavigationAction navigationAction: WKNavigationAction, decisionHandler: (WKNavigationActionPolicy) -> ()) {
    decisionHandler(WKNavigationActionPolicy.Cancel)
    // ...
}

Once you assign your own navigation delegate, Turbolinks will no longer invoke the Session delegate’s session:openExternalURL: method.

Note that your application must call the navigation delegate’s decisionHandler with WKNavigationActionPolicy.Cancel for main-frame navigation to prevent external URLs from loading in the Turbolinks-managed web view.

Customizing the Web View Configuration

Turbolinks allows your application to provide a WKWebViewConfiguration when you instantiate a Session. Use this configuration to set a custom user agent, share cookies with other web views, or install custom JavaScript message handlers.

let configuration = WKWebViewConfiguration()
let session = Session(webViewConfiguration: configuration)

Note that changing this configuration after creating the Session has no effect.

Setting a Custom User Agent

Set the applicationNameForUserAgent property to include a custom string in the User-Agent header. You can check for this string on the server and use it to send specialized markup or assets to your application.

configuration.applicationNameForUserAgent = "MyApplication"

Sharing Cookies with Other Web Views

If you’re using a separate web view for authentication purposes, or if your application has more than one Turbolinks Session, you can use a single WKProcessPool to share cookies across all web views.

Create and retain a reference to a process pool in your application. Then configure your Turbolinks Session and any other web views you create to use this process pool.

let processPool = WKProcessPool()
// ...
configuration.processPool = processPool

Passing Messages from JavaScript to Your Application

You can register a WKScriptMessageHandler on the configuration’s user content controller to send messages from JavaScript to your iOS application.

class ScriptMessageHandler: WKScriptMessageHandler {
    func userContentController(userContentController: WKUserContentController, didReceiveScriptMessage message: WKScriptMessage) {
        // ...
    }
}

let scriptMessageHandler = ScriptMessageHandler()
configuration.userContentController.addScriptMessageHandler(scriptMessageHandler, name: "myApplication")

document.addEventListener("click", function() {
    webkit.messageHandlers.myApplication.postMessage("Hello!")
})

Contributing to Turbolinks

Turbolinks for iOS is open-source software, freely distributable under the terms of an MIT-style license. The source code is hosted on GitHub. Development is sponsored by Basecamp.

We welcome contributions in the form of bug reports, pull requests, or thoughtful discussions in the GitHub issue tracker.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

© 2017 Basecamp, LLC