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Native Bridge Android

This Kotlin library is the native part of a RPC communication bridge between your app and the webview javascript. To function, it relies on a javascript counterpart to be setup.

The library has been tested on Android 4.4.4 and later, but will probably also work on older Android versions.

Note: For simplicity, we're using the term "webview javascript" to mean "the javascript hosted in a site shown in the webview".

Download

The library will soon be made available in a public Maven repo. Until then use the latest .aar in Releases.

The library has a dependency on Jackson 2.8.9, which needs to be added for the .aar to compile:

compile "com.fasterxml.jackson.core:jackson-core:2.8.9"
compile "com.fasterxml.jackson.core:jackson-databind:2.8.9"
compile "com.fasterxml.jackson.module:jackson-module-kotlin:2.8.9"

Usage

Instead of using android.webkit.WebView, use no.nrk.NativeBridgeWebView. If you're already extending WebView, you must instead extend NativeBridgeWebView.

For deserializing and serializing data, create classes implementing the TopicData.In and TopicData.Out interfaces. TopicData.In corresponds to the JSON received from the webview javascript, while TopicData.Out corresponds to the data we want to pass to the webview javascript.

You will then need to add a handler. The handler makes it possible for the native app and the webview javascript to communicate. To do this, use the nativeBridgeWebView.connection.addHandler(topic: String, callback: (T, WebViewConnection) -> Unit) function. The first parameter, topic, is a string that you and the developer responsible for implementing the javascript has agreed on. The webview javascript and the native app use the same topic to communicate. The second parameter is a closure, where T is your class implementing TopicData.In, and WebViewConnection is the webview.connection that can be used to send TopicData.Out to the webview javascript.

Example:

webview.connection.addHandler("someTopic", { _ : SomeTopic.In, connection ->
    connection.send("someTopic", SomeTopic.Out("data"))
  }
)

Error handling

If an error occurs, the app will pass data about this to the webview javascript, so the webview javascript can act accordingly.

If we have a topic available, the errors will be passed on the same topic. If not, the errors will be passed on the topic errors.

Possible errors

As of version 1.0.0, the following errors can be returned:

Error situation Error code Error message
Payload passed from webview cannot be deserialized to a topic. 1 Illegal payload format
Missing topic object in payload: a topic object was not found in the payload passed from the webview 2 Missing field: 'topic'
Missing data object in payload: a data object was not found in the payload passed from the webview 3 Missing field: 'data'
No topic handler defined for topic 4 Missing topic handler
Data doesn't match data expected by the topic handler 5 Invalid data for topic. Expected data topic '$topic'

Example error response:

When we're able to determine a topic:

{
  "topic": "someTopic",
  "errors": [
    {
      "code": 1,
      "message": "Missing topic handler"
    }
  ]
}

When we're not able to determine the topic, we will pass the errors on the errors topic:

{
  "topic": "errors",
  "errors": [
    {
      "code": 2,
      "message": "Missing field: 'topic'"
    }
  ]
}

License

MIT. See LICENSE.txt for details.