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Advanced Topics

Multiple Sessions

Each Session is 1:1 with a WKWebView. This means you can never have two pages active at the same time. You can create as many separate session as you need, though it's recommended to make as few as a possible. Every session you make will require a cold-boot visit which is likely to the be the slowest page load in your app. Each web view also uses additional resources.

One place you'll definitely want multiple sessions is for modals since non full-screen modals don't work out of the box with a single session. The demo shows a way to do this by lazily creating a reusable modal session whenever a modal is used. This is efficient, works well with any modal type, and makes the app feel better since we don't need to alter the main session at all to present/dismiss a modal.

A UITabBarController based app should work with a single session, but you may want to use multiple session there as well. A good rule of thumb is that you'll likely want a separate session for each navigation context you have (most likely a session per UINavigationController).

Native <-> JavaScript Integration

You can send messages from your native app to the web view by using session.webView.evaluateJavaScript() method. You can receive messages by adding a WKScriptMessageHandler to the web view and implementing the required protocols. That allows for two-way async communication.

Here's a simple sketch of how this works. You can create your session with a WKWebViewConfiguration and in that configuration, you can setup your WKScriptMessageHandler which will be used to receive messages from the web app through JavaScript. When you receive a message, you can parse it and handle it however you need, optionally sending data back to the web app with the webView.evaluateJavaScript() method.

import Turbo
import WebKit

// WKScriptMessageHandler requires NSObject conformance
class SessionController: NSObject {
    lazy var session: Turbo.Session = {
        let configuration = WKWebViewConfiguration()
        
        // Setup your session with a WKWebViewConfiguration and script message handler
        configuration.userContentController.add(self, name: "nativeApp")
        
        let session = Turbo.Session(webViewConfiguration: configuration)
        session.delegate = self
        
        return session
    }()
}

extension SessionController: WKScriptMessageHandler {
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        // WebView JS sends a message with
        // webkit.messageHandlers.nativeApp.postMessage(message)
        
        // Native app receives message and processes it as needed, maybe pass to another object
        // message.body...
        
        // Native app can call more JS functions as needed
        session.webView.evaluateJavaScript("someReplyMessage()")
    }
}

This is fine for simple tasks, but we've found we need something more comprehensive for our apps, which is why we created a new framework called Strada. This is a library in 3 parts (web, iOS, and Android) for integrating Turbo Native apps with their hosted web apps. This is separate and optional, but can dramatically improve the experience of your app. See the Strada repo for details (coming soon).