How to Build an iMessage Extension for a React Native App (Part 2)
In this post, I will show you how we built an iMessage extension by writing a bridge for our React Native-based mobile app.
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In this post, I will show you how we built an iMessage extension by writing a bridge for our React Native-based mobile app. This approach took our team around two weeks to explore and might save you significant time if you have a similar intention. This is part two out of two (you can find Part 1 here).
When we set out to build an iMessage extension for Lisk Mobile using React Native, we immediately hit an exciting challenge. As it turns out, when it comes to third-party applications, Apple likes developers to play by its own rules. If a company wants to benefit from the features of the tech giant's operational systems and rich user base, it needs to be built using Apple's own tools and programming language. iPhone's iMessage is definitely worth this hassle. It has proven to be a big hit since its release in 2016. Within the first six months, iMessage generated thousands of innovative in-messenger extensions including those created by Airbnb and Dropbox. Late in 2018, Mark Zuckerberg admitted this feature is one of Facebook's 'biggest competitors by far.' Since the release of Lisk Mobile during Lisk's Berlin meetup in October 2018, our team has been busy implementing features such as Face ID Authentication, as well as developing blockchain-specific solutions. Identifying the opportunity to extend the iMessage option for our users, we got to work on our own integration.
The first option was to look for existing React Native component and educational material. Unfortunately, we could not find official documentation or up-to-date resources due to the fast pace of change in both React Native and native iOS development.
The second option was to try native iOS development within the Lisk Mobile codebase. The benefit of this approach was example projects and conference talks provided by Apple. However, introducing a considerable amount of Swift or Objective-C into the codebase was not desirable. Such a move would cause too much code duplication due to us having to rewrite most of our existing business logic and UI components.
After careful evaluation, we decided to take an alternative route: writing our own bridge implementation. In the rest of this article, we will explain how we did it. If you want to jump straight into code, we've also created this handy demo project on GitHub.
Creating Bridge Modules
In this section, we are going to create our helpers and modules on the Swift side in order to expose the required methods and events to communicate with the React Native side.
Creating a Mapper for Swift - JS Communication
Since we are going to send data from Swift to React Native, it would be nice to create a mapper utility for formatting that data properly.
Creating a Manager for MessagesViewController
Now we are going to create a module named
MessagesManager that has a connection with our main
MessagesViewController and will help us to interact with from the React Native side.
Initial structure of MessagesManager.swift
Since we are creating that custom class with Swift, we also need to provide the interface file to make sure it's recognized as a native module by React Native.
MessagesManager.rn file that contains interface declaration for React Native
Creating an EventEmitter for MessagesViewController
In addition to the helper methods we have provided in the previous section, now we will create another class by following the EventEmitter guide from the official React Native documentation.
Updates we have made on MessagesViewController file in order to use protocol pattern
Initial structure of MessagesEventEmitter
MessagesEventEmmiter.rn file that contains interface declaration for React Native
First of all, we update our
MessagesViewController to define a protocol that can be easily implemented by
MessagesEventEmitter to reduce the effort we need to make (and encourage separation of concerns) in order to follow an event-based design pattern.
Custom Module Initializer
If you create a native module with React Native by following the basic flow, you'll end up with a pre-instantiated object that is created during the initialization step of the bridge. If it was a regular iOS application, we would have a chance to communicate with the root view controller by using UIApplication's shared property but that's not what we were exactly looking for.
Considering that our Native Module needs to be stateful to communicate with the
MessagesAppViewController instance, we ended up creating a custom module initializer by following an approach derived from the dependency injection guide in the React Native documentation.
Custom ModuleInitializer that allows us to use dependency injection pattern at the initialization step of MessagesManager and MessagesEventEmiiter modules.
Then we will update the
presentReactNative method of
MessagesViewController to use that custom module initializer.
Updating related parts of MessagesViewController to use custom module initializer
Consuming Native Modules on React Native
Now that we have covered pretty much all the things we need from our native modules, we can start playing with them on the React Native side.
Updating Presentation Style
Making use of getPresentationStyle and updatePresentationStyle methods on the React Native side
So far so good, huh? But we forgot something. Let's look at the recording below and try to catch what's missing.
Since we are not listening to the events related to the presentation style changes triggered by the native UI, we end up in a loop with the sheet continually opening, we don't have the correct value of
presentationStyle right after it's been updated. In order to resolve this, we are going to use the
This will allow the sheet to receive updates on state from both the native Swift environment (for when users manually close the sheet) and from within our React Native app.
Using MessagesEventEmitter for listening to changes on presentationSytle
Now the app responds to both triggers from the codebase, and users manually close or open the sheet.
Composing a Message
Now we are so close to our main goal, composing an iMessage from the React Native side!
Let's start with initializing our blueprint to create the data of a message object that we can through our
Using the composeMessage method of MessagesManager to create a test message.
Assests section of Xcode where we add images in order to use the Message templates.
Outcome of the test message
Using the URL Field to Share Data
Now that we are able to compose and send a message, we can create a very simple example to demonstrate the usage of the URL field.
What we are going to do is to put a timestamp and the identifier of the sender to the URL field and present it on the screen. We will also make use of the
getActiveConversation method exposed by
MessagesManager, as well as the
didSelectMessage events from the
Updating App.iMessage.js to make use of URL field
Now if we send a message as Kate to John (or vice-versa) we can observe the change in the timestamps and the sender IDs.
Sending a message as Kate to John. Kate's sender ID is CD8FB32C-4683-669C6E42DDF8
Opening and replying to Kate's message as John. John's sender ID is 721FA6A5-CC6F-42FD-4B846E634E62
If you want to share more data and handle complex logic, our recommendation is to use a third-party library for simplifying the URL construction and parsing logic. For a better example, you can check out the iMessage part of our open source Lisk Mobile application.
Mysterious Simulator Crash
When the application is run from Xcode, there's a crash that happens right after we go back from the message detail screen to the list screen. We haven't found the crux of this problem but we were able to reproduce it with the example project from Apple's official documentation.
Our workaround for the crash is to stop Xcode right after we get everything running. It will make more sense if you take a look at the 'Remote Debugger and Reload Menu for Development' section below.
Less Mysterious iOS 10 Crash
Unfortunately, we couldn't make our iMessage extension run successfully within a simulator that has iOS 10. The interface of the iMessage extensions has been updated when there's a migration from iOS 10 to 11. It might be related to that update but there was not enough information for us to track the problem so we ended up choosing iOS 11 as our deployment target of the iMessage extension.
Not Sure if Bug or Feature: Simulator Refreshes Participant IDs
While running the iMessage extension in the simulator, the participant identifiers coming from the
activeConversation object of Kate and John which are changed each time you compose a message. Whether it stems from a bug or a feature remains to be seen, but we had to run the application on testing devices in order to make sure our participant identifier logic worked properly.
Remote Debugger and Reload Menu for Development
Considering the mysterious simulator crash we mentioned in the section above, this whole experience is kind of painful for developers coming from the realm of hot reloading with time travel. In order to improve the developer experience, we have implemented a little utility by using the DevSettings module provided by React Native.
And import it to our App.iMessage.js component as following:
Usage of DevMenu component within the root iMessage component
Unfortunately, the DevSettings module does not export a method to get the value of the
remoteDebugging flags so we need to double click the buttons within our component to make sure we sync their state correctly.
Deep Link Opener
In our Lisk Mobile application, we also needed a utility for opening the main application and redirecting the user to a specific deep link. We have resolved this issue by enhancing the
After setting up the main application to handle deep links by following the guide from official React Native documentation, the next step is to update the
MessagesManager to provide a utility for opening deep links.
We have added the openURL method to MessagesManager
Also updated the interface file of the MessagesManager to contain the openURL method
Usage of the openURL method on the React Native side
The openURL method in action!
Display a Loading View During the Initial Load
The natural behavior of iMessage extensions is to show the application logo uploaded in the assets section during the initial load as shown below.
Default behavior of the launch screen
In our case, we are also waiting for the React Native bundle to be loaded until we see something to interact on the screen. Luckily,
RCTRootView has a property named
loadingView that allows us to provide a temporary view to be shown while the bundle is loading.
In order to enhance this experience, let's create a view with the activity indicator and assign it to the
loadingView property of
Using the storyboard to set the layout of the LoadingView
Updating the presentREactNative method of the MessagesViewController to make sure our RCTRootView instance uses LoadingView
End result of this section: LoadingView is presented until the React Native bundle is loaded
Controlling the Loading View From the React Native Side
Now that we have our blueprint for displaying that loading view, we can also put in a little effort to make it controllable from the React Native side.
This would be very handy if there's a case you need to delay the initial render (e.g. fetching data from the server) and don't want to deal with creating another loading view that covers full screen for such a task.
presentReactNativeView method of
MessagesViewController needs to be refactored a little bit as follows:
The presentReactNative method initializes and presents a LoadingView on top of the RCTRootView, instead of using the RCTRootView.loadingView property
In order to control the presence of that loadinView, we have added two methods to the MessagesManager
Updated interface file of the MessagesManager to contain methods for controlling the loadingView
Now it's time to make use of those freshly added methods on the React Native side. What we are going to do is to fake an asynchronous task in
componentDidMount and delay the initial rendering of the content until that task is completed. We will also add an additional button to the sample set to toggle the loading screen again.
Making use of loadingView related methods on the React Native side
Working on user-facing applications in an insular software environment such as that of Apple requires innovative solutions. While Apple definitely provides comprehensive documentation aimed at helping developers coding with native iOS, connecting the existing pieces to the native ecosystem is another thing altogether. After deciding to implement an iMessage extension for the React Native-based Lisk Mobile, we experienced this obstacle first hand. Nonetheless, we found writing a bridge between React Native and the native iOS-based app an exciting and educational experience. We hope this tutorial will save you time in implementing a similar feature to your React Native application as well!
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