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Building an iOS Plugin

iOS Tutorial App

For the purpose of the tutorial, we will assume you already have an existing iOS application in which you have a feed or list of items. As the Flipper team, we obviously concern ourselves mostly with sea mammals, so this is what our app displays. The actual display logic is not what's interesting here, but how we can make this data available in our Flipper desktop app.

You can find the source code of the project on GitHub.

Creating a Plugin

On iOS, a Flipper plugin is a class that implements the FlipperPlugin interface.

The interface is rather small and only comprises four methods:

  • (NSString *)identifier: Specify a unique string so the JavaScript side knows where to talk to. This must match the name attribute in the package.json we will look into later in this tutorial.
  • (void)didConnect:(id<FlipperConnection>)connection: This method is called when the desktop client connects and is ready to receive or send data.
  • (void)didDisconnect: We're sure you can figure this one out.
  • (BOOL)runInBackground: Unless this is true, only the currently selected plugin in the Flipper UI can communicate with the device. Its an optional method which you can override. Default value used is false.

Let's implement these methods for our sealife app:

import Foundation
import FlipperKit

class SeaMammalsPlugin: NSObject, FlipperPlugin {
var connection: FlipperConnection? = nil
let mammals: [MarineMammal]

init(_ marineMammals: [MarineMammal]) {
mammals = marineMammals

func identifier() -> String! {
return "sea-mammals"

func didConnect(_ connection: FlipperConnection!) {
self.connection = connection
for (index, mammal) in mammals.enumerated() {
connection.send("newRow", withParams: ["id": index, "title":, "url": mammal.image.absoluteString])

func didDisconnect() {
connection = nil;

The two interesting bits here are didConnect and connection.send. connection.send sends a message to the desktop app and is identified with the name "newRow".

For our sample app, we're dealing with a static data source. However, in real life, you will likely dynamically receive new data as the user interacts with the app. So while we just send all the data we have at once in didConnect, you would normally set up a listener here to instead call connection.send("newRow", params) as new data arrives. params are nothing but a dictionary which contains the data which you want to send over the wire to the desktop app.

Registering your Plugin

Now all you need to do is let Flipper know about your new plugin. You do this by calling add on your FlipperClient, which is normally created at application startup.

let client = FlipperClient.shared()
// Add all sorts of other amazing plugins here ...

What next

When starting your application now, Flipper will tell the desktop application about the plugin it supports, including "sea-mammals" and will look for a corresponding JavaScript plugin by that name. Before building it's JavaScript counterpart, first lets build a Flipper Plugin in Android.