Question

I tried looking for a similar post but couldn’t find any, hence posting this query for your help. Essentially, I have a custom UI created on the GWT side. Now, I want to send events occuring at the GWT side over to the javascript/jsp page. For this I was wondering if there’s a way for the jsp/javascript to register a method in the GWT code, and whenever, any event happens at the GWT side, the GWT java code can simply invoke this javascript method (which is like a function pointer/object), and the information would be notified at the jsp page. Though I can directly call javascript methods from within the GWT code, however, that means that the GWT code also need to know the javascript method name, and this results in a tight coupling. Instead the javascript could simply pass in a handle to the function to the GWT code, which would simply invoke this handle to pass in necessary events on the jsp/javascript code. Any ideas would be very helpful.

Answer 1

You can use a Dictionary to pass the function name to your application.

In the JSP host page:

<script type="text/javascript">
  function myFunction() {
    // Do stuff...
  }

  var MyDictionary = {
    myCallback = "myFunction"
  };
</script>

And in your application:

public void onEvent(EventType event) {
  Dictionary d = Dictionary.getDictionary("MyDictionary");
  invokeNativeCallback(d.get("myCallback"));
}

private native void invokeNativeCallback(String callbackName) /*-{
  if (typeof $wnd[callbackName] === "function") {
    $wnd[callbackName]();
  }
}-*/;