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How to Communicate with a Portal Web Application

The PortalsPlugin provides useful features to aid in communication between your Web and Native applications. It is included in the Ionic Portals library by default and takes advantage of the Capacitor Plugin system.

Setup

Android

Follow the Getting Started Guide to install the Ionic Portals library into your native mobile projects. The PortalsPlugin is automatically added to every instance of a Portal.

Web

Install the Ionic Portals package from NPM into your web application.

npm install @ionic/portals

Initial Context

The Initial Context mechanism allows you to pass data to your web application from native so that it is available for when the web application initially loads.

Setting Initial Context

Initial context data can be set in two different ways. You may want to set it when building a new Portal using PortalManager.

PortalManager.newPortal("maps")
    .setStartDir("web")
    .setInitialContext(mapOf("ic_example" to "hello world"))
    .create()

You can also set Initial Context data on a Portal object prior to the Portal loading.

val mapsPortal = PortalManager.getPortal("maps")
mapsPortal?.setInitialContext(mapOf("ic_example" to "hello world"))

Using Initial Context

To access the initial context set from the native application in your web application, import getInitialContext from @ionic/portals use the getInitialContext() function.

import { getInitialContext } from "@ionic/portals";

const initialContext = getInitialContext<{ ic_example: string }>();
// prints "hello world" in this example
console.log(initialContext?.value?.ic_example);

Initial context is useful when using a Single Page Application (SPA) across multiple Portals in your application. The route to a specific section of the SPA can be passed in as initial context data. Your web application can then use it to load that section directly without need for a redirect. Check out our how-to guide.

Communicating via Pub/Sub

The Publish and Subscribe mechanism (pub/sub) relies on two parts that work together: PortalsPubSub and PortalsPlugin. PortalsPubSub is the class that manages a message bush to subscribe and publish messages to, while PortalsPlugin is the Capacitor plugin that exposes the functionality of PortalsPubSub to a Portal web application. By default, PortalsPlugin uses PortalsPubSub.shared for communication, but a custom instance of PortalsPubSub can be created and passed to the PortalsPlugin initializer to enable isolating events from other Portals.

In this example, foo and bar portals cannot see events published by the other and cannot listen for events published by the native application unless the events were published through the PortalsPubSub instance it was configured with:

val fooPubSub = PortalsPubSub()
val barPubSub = PortalsPubSub()

val fooPortal = PortalBuilder("foo")
  .addPluginInstance(PortalsPlugin(fooPubSub))
  .create()

val barPortal = PortalBuilder("bar")
  .addPluginInstance(PortalsPlugin(barPubSub))
  .create()

If fooPortal and barPortal were configured without adding the custom PortalsPlugin instance, then they would both receive events through PortalsPubSub.shared.

Defining Subscribers

Subscribers listen for messages sent to a certain topic. They can be defined in your web application to listen for messages published from native, and vice versa.

To listen for a message published from the native side of a Portal, define a subscriber in your web application.

import { subscribe } from '@ionic/portals';

const portalSubscription = await subscribe({ topic }, (result) => {
  console.log(JSON.stringify(result));
});

To listen for messages published from the web side of a Portal, define a subscriber in your native application.

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // ...

    val portal = PortalManager.getPortal("example")
    val portalFragment = PortalFragment(portal)

    // listen on the topic "dismiss" and act on the result data.
    // This is an example to dismiss a containing native DialogFragment.
    dismissSubscription = PortalsPubSub.shared.subscribe("dismiss") { result ->
        if (result.data == "cancel" || result.data == "success") {
            this.dismiss()
        }
    }

    // ...

    // add the PortalFragment to the example container fragment
    val fragmentManager = childFragmentManager
    fragmentManager.beginTransaction().replace(R.id.example_web_app, portalFragment!!).commit()
}

When finished with the Portal, call the unsubscribe function to clean up your subscription to avoid potential memory leaks.

override fun onDestroy() {
    // dismissSubscription is an integer value returned when
    // calling PortalsPubSub.shared.subscribe
    PortalsPubSub.shared.unsubscribe("dismiss", dismissSubscription)
    super.onDestroy()
}

Subscribe Using Annotations

Android also provides a way to link subscribers defined as functions with @PortalMethod annotations. An instance of the class containing the annotated functions can then be provided to the PortalFragment using the linkMessageReceivers function. See the example below for implementation details.

note

When using this method of adding subscribers, the Portals library will handle subscribing and unsubscribing automatically for you. Calling PortalsPubSub.subscribe and PortalsPubSub.unsubscribe is not required. If your portal has been configured with a custom PortalsPubSub instance, it must also be passed to the overload of linkMessageReceivers that accepts a PortalsPubSub argument.

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // ...

    val portal = PortalManager.getPortal("example")
    val portalFragment = PortalFragment(portal)

    // register this class as having defined message subscribers
    portalFragment!!.linkMessageReceivers(this)

    // ...

    // add the PortalFragment to the example container fragment
    val fragmentManager = childFragmentManager
    fragmentManager.beginTransaction().replace(R.id.example_web_app, portalFragment!!).commit()
}

/**
 * Define a `dismiss` method to receive messages on the "dismiss"
 * topic and act on the message. This is an example to dismiss
 * a containing native DialogFragment.
 */
@PortalMethod
fun dismiss(result: String?) {
    if (result != null && (result == "cancel" || result == "success")) {
        this.dismiss()
    }
}

Publishing Messages

Publish messages to send data through a Portal to registered Subscribers.

From Web to iOS/Android

To send a message from your web application to iOS or Android, use the Portals.publish() function.

import { publish } from '@ionic/portals';

publish({ topic: "dismiss", data: "success" });

From Android to Web

To send messages from your native application to the web application, use the PortalsPubSub.publish() methods.

PortalsPubSub.shared.publish("weather", "sunny")

Examples

The PortalsPlugin is used in the E-Commerce App demo.