WebMessagePortCompat

@AnyThread
public abstract class WebMessagePortCompat

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 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 types

The listener for handling MessagePort events.

Public methods
abstract void
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_CLOSE, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
close()

Close the message port and free any resources associated with it.
abstract void
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_POST_MESSAGE, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
postMessage(@NonNull WebMessageCompat message)

Post a WebMessage to the entangled port.
abstract void
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
setWebMessageCallback(
    @NonNull WebMessagePortCompat.WebMessageCallbackCompat callback
)

Sets a callback to receive message events on the main thread.
abstract void
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
setWebMessageCallback(
    @Nullable Handler handler,
    @NonNull WebMessagePortCompat.WebMessageCallbackCompat callback
)

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

Public methods

close

Added in 1.1.0
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_CLOSE, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
public abstract void close()

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

This method should only be called if isFeatureSupported returns true for WEB_MESSAGE_PORT_CLOSE.

postMessage

Added in 1.1.0
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_POST_MESSAGE, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
public abstract void postMessage(@NonNull WebMessageCompat message)

Post a WebMessage to the entangled port.

This method should only be called if isFeatureSupported returns true for WEB_MESSAGE_PORT_POST_MESSAGE.

When posting a WebMessageCompat with type TYPE_ARRAY_BUFFER, this method should check if isFeatureSupported returns true for WEB_MESSAGE_ARRAY_BUFFER. Example: 

if (message.getType() == WebMessageCompat.TYPE_ARRAY_BUFFER) {
    if (WebViewFeature.isFeatureSupported(WebViewFeature.WEB_MESSAGE_ARRAY_BUFFER) {
        // ArrayBuffer message is supported, send message here.
        port.postMessage(message);
    }
}
Parameters
@NonNull WebMessageCompat message

the message from Java to JS.
Throws
java.lang.IllegalStateException

If message port is already transferred or closed.

setWebMessageCallback

Added in 1.1.0
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
public abstract void setWebMessageCallback(
    @NonNull WebMessagePortCompat.WebMessageCallbackCompat callback
)

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

This method should only be called if isFeatureSupported returns true for WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK.

Parameters
@NonNull WebMessagePortCompat.WebMessageCallbackCompat callback

the message callback.

setWebMessageCallback

Added in 1.1.0
@RequiresFeature(name = WebViewFeature.WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK, enforcement = "androidx.webkit.WebViewFeature#isFeatureSupported")
public abstract void setWebMessageCallback(
    @Nullable Handler handler,
    @NonNull WebMessagePortCompat.WebMessageCallbackCompat callback
)

Sets a callback to receive message events on the handler that is provided by the application. If the handler is null the message events are received on the main thread.

This method should only be called if isFeatureSupported returns true for WEB_MESSAGE_PORT_SET_MESSAGE_CALLBACK.

Parameters
@Nullable Handler handler

the handler to receive the message events.
@NonNull WebMessagePortCompat.WebMessageCallbackCompat callback

the message callback.