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Custom Native iOS Code

With Capacitor, you are encouraged to write Swift or Objective-C code to implement the native features your app needs.

There may not be a Capacitor plugin for everything–and that’s okay! It is possible to write WebView-accessible native code right in your app.

WebView-Accessible Native Code

The easiest way to communicate between JavaScript and native code is to build a custom Capacitor plugin that is local to your app.

EchoPlugin.swift

First, create a EchoPlugin.swift file by opening Xcode, right-clicking on the App group (under the App target), selecting New File… from the context menu, choosing Swift File in the window, and creating the file.

New Swift File in Xcode

Copy the following Swift code into EchoPlugin.swift:

import Capacitor

@objc(EchoPlugin)
public class EchoPlugin: CAPPlugin {
    @objc func echo(_ call: CAPPluginCall) {
        let value = call.getString("value") ?? ""
        call.resolve(["value": value])
    }
}

The @objc decorators are required to make sure Capacitor’s runtime (which must use Objective-C for dynamic plugin support) can see it.

Register the Plugin

We must register custom plugins on both iOS and web so that Capacitor can bridge between Swift and JavaScript.

EchoPlugin.m

Next, create a EchoPlugin.m file with Xcode in the same way, but choose Objective-C in the window. Leave the File Type as Empty File. If prompted by Xcode to create a Bridging Header, click Create Bridging Header.

Using Xcode to create native files is recommended because it ensures the references are added to the project appropriately.

These changes to project files should be committed to your project along with the new files themselves.

Copy the following Swift code into EchoPlugin.m:

#import <Capacitor/Capacitor.h>

CAP_PLUGIN(EchoPlugin, "Echo",
    CAP_PLUGIN_METHOD(echo, CAPPluginReturnPromise);
)

These Objective-C macros register your plugin with Capacitor, making EchoPlugin and its echo method available to JavaScript. Whenever you add or remove methods in EchoPlugin.swift, this file must be updated.

JavaScript

In JS, we use registerPlugin() from @capacitor/core to create an object which is linked to our Swift plugin.

import { registerPlugin } from '@capacitor/core';

const Echo = registerPlugin('Echo');

export default Echo;

The first parameter to registerPlugin() is the plugin name, which must match the second parameter to the CAP_PLUGIN macro in EchoPlugin.m.

TypeScript

We can define types on our linked object by defining an interface and using it in the call to registerPlugin().

 import { registerPlugin } from '@capacitor/core';

+export interface EchoPlugin {
+  echo(options: { value: string }): Promise<{ value: string }>;
+}

-const Echo = registerPlugin('Echo');
+const Echo = registerPlugin<EchoPlugin>('Echo');

 export default Echo;

The generic parameter of registerPlugin() is what defines the structure of the linked object. You can use registerPlugin<any>('Echo') to ignore types if you need to. No judgment. ❤️

Use the Plugin

Use the exported Echo object to call your plugin methods. The following snippet will call into Swift on iOS and print the result:

import Echo from '../path/to/echo-plugin';

const { value } = await Echo.echo({ value: 'Hello World!' });
console.log('Response from native:', value);

Next Steps

Read the iOS Plugin Guide ›

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