gwt/jsni- Pass a String from external JS to Java

Question

How can I call from external JS with JSNI?

For example:

//Some external JS code 
         ...
        this.onFeatureClick = function(event) {
        ...
        var name = "Batman";
        passToJava(name); //Invoke java method and pass String name
        };

I tried this here:

 public void onModuleLoad() {
     ...
     nativeVariableName(); //Call native method
 }

 public static void passToJava(String name) {
    System.out.println(name);
 }

public native String nativeVariableName() /*-{
            $wnd.passToJava = function(name) {
            @com.google.myproject.webinterface.client.MyWebInterface::passToJava(Ljava/lang/String;)(name);
            }; }-*/;

I don't even know if the call from JavaScript works. Thanks.

take a look at the gwt docs, the first section explains how to send a variable from JavaScript to Java: code.google.com/webtoolkit/doc/latest/… — milan
– milan, Commented Jan 8, 2012 at 21:00
public static native void alert(String msg) /*-{ $wnd.alert(msg); }-*/; — milan
– milan, Commented Jan 8, 2012 at 21:00

jusio · Accepted Answer · 2012-01-08 23:55:56Z

2

This code works just fine. I don't know where do you expect to see result of invocation of System.out.println, but looks like you are looking into wrong place. Replace System.out.println with Window.alert and see for yourself. If it doesn't work, it means that error is in some other place:

Check if the function is correctly exposed (open console in browser, and type window.passToJava, if it displays null, function wasn't exposed)
Check if onFeatureClick is called correctly.

answered Jan 8, 2012 at 23:55

jusio

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2 Comments

Robert Petermeier Over a year ago

Another way of printing debug messages is to use the method com.google.gwt.core.client.GWT.log(String). That way, it will be visible in the console utility for the hosted mode. That way only developers will ever see such messages but users will never be bothered even if you forget to remove the calls later.

myX. Over a year ago

Thanks, it helped. If I add a function passToJava(){...} in the external JS code, then the call works onclick. However, nothing happens in my gwt code.

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