I am not a JS developer and use it pretty much by example, so it might
be that I am missing something really basic below.
I have come across problems using JSNI in the following 2 scenarios:
1.
I use Google Visualization API successfully in JS as follows:
********************
HTML file
<script type="text/javascript" src="http://www.google.com/jsapi";></
script>
JS file
google.load('visualization', '1', {'packages':['piechart']}); //
<== future JSNI problems occur here
var chart = new google.visualization.LineChart
(document.getElementById('GoogleVisChart'));
// other JS commands to draw the chart
**********
and then try to write a wrapper using GWT JSNI as follows:
********************
HTML file
<script type="text/javascript" src="http://www.google.com/jsapi";></
script>
JAVA file
class GChart {
static { _init(); }
private static native void _init() /*-{ // <=== ERROR at this
function
$wnd.google.load('visualization', '1', {'packages':
['piechart']});
}-*/;
JavaScriptObject gvis;
public GChart( String id ) { gvis = _chart( id ); }
private native JavaScriptObject _chart( String id ) /*-{
return new $wnd.google.visualization.LineChart
($wnd.document.getElementById( id ) );
}-*/;
// methods to draw the chart through native functions
**********
The GWT compiler gives the following error for the above code
********************
[ERROR] Unable to load module entry point class
com.google.gwt.app.testGViz.client.TestGViz (see associated exception
for details)
java.lang.RuntimeException: Failed to invoke native method:
@com.google.gwt.app.testGViz.client.GChart::_init() with 0 arguments.
at com.google.gwt.dev.shell.moz.LowLevelMoz.invoke(LowLevelMoz.java:
132)
at com.google.gwt.dev.shell.moz.ModuleSpaceMoz.doInvoke
(ModuleSpaceMoz.java:98)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:
447)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid
(ModuleSpace.java:248)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid
(JavaScriptHost.java:107)
at com.google.gwt.app.testGViz.client.GChart._init(GChart.java)
at com.google.gwt.app.testGViz.client.GChart.<clinit>(GChart.java:7)
at com.google.gwt.app.testGViz.client.TestGViz.onModuleLoad
(TestGViz.java:21)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke
(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke
(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:320)
at com.google.gwt.dev.shell.BrowserWidget.attachModuleSpace
(BrowserWidget.java:329)
at com.google.gwt.dev.shell.moz.BrowserWidgetMoz.access$100
(BrowserWidgetMoz.java:35)
at com.google.gwt.dev.shell.moz.BrowserWidgetMoz
$ExternalObjectImpl.gwtOnLoad(BrowserWidgetMoz.java:59)
at org.eclipse.swt.internal.gtk.OS._g_main_context_iteration(Native
Method)
at org.eclipse.swt.internal.gtk.OS.g_main_context_iteration(OS.java:
1428)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:2840)
at com.google.gwt.dev.GWTShell.pumpEventLoop(GWTShell.java:720)
at com.google.gwt.dev.GWTShell.run(GWTShell.java:593)
at com.google.gwt.dev.GWTShell.main(GWTShell.java:357)
**********
Moving the statement in the native _init function to the constructor
does not help either. To get it to work, I have to move it out to the
HTML file
********************
HTML file
<script type="text/javascript" src="http://www.google.com/jsapi";></
script>
<script type="text/javascript">
google.load('visualization', '1', {'packages':['piechart']});
</script>
**********
This was also suggested in
http://groups.google.com/group/Google-Web-Toolkit/browse_thread/thread/583dc26de8595958/bcbb4d6bb7236f22?lnk=gst&q=jsni&utoken=qRnbnjUAAAB8wAYSTNbu8_hi0ZNe2Xc4tU3gpchqHpzsKQqE7zGIYkIWfTZ5-aftLfGBx4hvV6kGKZOOAsC6ELWUwMHP3Sz1
Although this works, I do not understand why I could no do the
google.load through JSNI.
In the meanwhile, this is not an issue as GWT now provides its own
wrappers for the Google Visualization API. But, I would still like to
understand the error.
2.
I am trying this time to write a wrapper for another Visualization
library, Protovis. An example JS use case is as follows:
********************
HTML file
<script type="text/javascript" src="protovis.js"></script>
JS file
var vis = new pv.Panel().canvas("PVis"); // <== future JSNI
problems occur at this point
var line = vis.add(pv.Line);
// add data and attributes to line
vis.render();
**********
I write a GWT wrapper as follows
********************
JAVA file
class PChart {
JavaScriptObject pvis;
public PChart( String id ) { pvis = _chart( id ); }
private native JavaScriptObject _chart( String id ) /*-{
return new $wnd.pv.Panel().canvas( id ); // <=== ERROR at
this line
} -*/;
// other stuff
**********
The GWT compiler returns the following error at the indicated line
********************
com.google.gwt.core.client.JavaScriptException: (TypeError): $wnd.pv
has no properties
**********
I do not understand what I am doing wrong. Can someone help me to get
this to work?
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