Re: JSNI - reference Java method from native JS method

On Sunday, October 19, 2014 1:46:42 AM UTC+2, Magnus wrote:

Hi,

I want to define a hover handler in Java and reference it from JavaScript in order to register it in a JS library:

But the reference causes an error:

public class MyClass

{

public native void myHandler (JavaScriptObject e) // don't know if JavaScriptObject is the right type

You could also use com.google.gwt.dom.client.NativeEvent (and wouldn't need JSNI).

 

 /*-{

    var c = e.target.className;

    console.log (c);

 }-*/;

 private native void startHover (String stl_w)

 /*-{

  var f = this.@mylib.myWidget::myhandler; // produces syntax error

Should be this.@mylib.myWidget::myHandler(Lcom/google/gwt/core/client/JavaScriptObject;), or this.@mylib.myWidget::myHandler(*), or just this.@myWidget::myHandler(*) in GWT 2.7 (resolves class names relative to package and imports).

 

  $wnd.myLib.hover (f); // register handler in the external library

That won't work the way you expect it to, because the 'this' inside myHandler won't be an instance of MyClass/myWidget.

Exceptions occurring inside myHandler also won't be dispatched to GWT.UncaughtExceptionHandler, and scheduled commands (scheduleEntry, and scheduleFinally within myHandler) won't work; for that you need to wrap the function with $entry: f = $entry(f).

This would work best:

var self = this;

 $wnd.myLib.hover($entry(function(e) { self.@myWidget::myHandler(*)(e); }));

To sum up: your errors here are related to JSNI method reference syntax, and scope and 'this' in JavaScript.

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