WebMessagePort

Kotlin |Java

abstract class WebMessagePort

kotlin.Any
↳	android.webkit.WebMessagePort

The Java representation of the HTML5 message ports.

A Message port represents one endpoint of a Message Channel. In Android webview, there is no separate Message Channel object. When a message channel is created, both ports are tangled to each other and started, and then returned in a MessagePort array, see WebView.createWebMessageChannel for creating a message channel.

When a message port is first created or received via transfer, it does not have a WebMessageCallback to receive web messages. The messages are queued until a WebMessageCallback is set.

A message port should be closed when it is not used by the embedder application anymore. A closed port cannot be transferred or cannot be reopened to send messages. Close can be called multiple times.

When a port is transferred to JS, it cannot be used to send or receive messages at the Java side anymore. Different from HTML5 Spec, a port cannot be transferred if one of these has ever happened: i. a message callback was set, ii. a message was posted on it. A transferred port cannot be closed by the application, since the ownership is also transferred.

It is possible to transfer both ports of a channel to JS, for example for communication between subframes.

Summary

Nested classes
abstract	`WebMessageCallback` The listener for handling MessagePort events.

Public methods
abstract Unit	`close()` Close the message port and free any resources associated with it.
abstract Unit	`postMessage(message: WebMessage!)` Post a WebMessage to the entangled port.
abstract Unit	`setWebMessageCallback(callback: WebMessagePort.WebMessageCallback!)` Sets a callback to receive message events on the main thread.
abstract Unit	`setWebMessageCallback(callback: WebMessagePort.WebMessageCallback!, handler: Handler!)` Sets a callback to receive message events on the handler that is provided by the application.

Public methods

close

Added in API level 23

abstract fun close(): Unit

Close the message port and free any resources associated with it.

postMessage

Added in API level 23

abstract fun postMessage(message: WebMessage!): Unit

Post a WebMessage to the entangled port.

Parameters
`message`	WebMessage!: the message from Java to JS.

Exceptions
`java.lang.IllegalStateException`	If message port is already transferred or closed.

setWebMessageCallback

Added in API level 23

abstract fun setWebMessageCallback(callback: WebMessagePort.WebMessageCallback!): Unit

Sets a callback to receive message events on the main thread.

Parameters
`callback`	WebMessagePort.WebMessageCallback!: the message callback.

setWebMessageCallback

Added in API level 23

abstract fun setWebMessageCallback(
    callback: WebMessagePort.WebMessageCallback!, 
    handler: Handler!
): Unit

Sets a callback to receive message events on the handler that is provided by the application.

Parameters
`callback`	WebMessagePort.WebMessageCallback!: the message callback.
`handler`	Handler!: the handler to receive the message messages.