registerMessageHandler method
Registers the registrar's message handler (handlePlatformMessage) with the engine, so that plugin messages are correctly dispatched to the relevant registered plugin.
Only one handler can be registered at a time. Calling this method a second time silently unregisters any previously-registered handler and replaces it with the handler from this object.
This method uses a function called setPluginHandler
in
the dart:ui_web library. That function is only available when
compiling for the web.
Implementation
void registerMessageHandler() {
ui_web.setPluginHandler(handleFrameworkMessage);
}