JSNI - invoke Java method from JS function

Question

I am trying to invoke a java method right from my JSNI function but for some reason it never works. What am I doing wrong here? :(

Here is my code

/**
   For UI button click method...
*/
private native void test(String param)
/*-{

var a=(function b(p)
{
 this.@com.(...).TestClass::setTest(Ljava/lang/String;)(p);

})(param);

}-*/

private void setTest(String param){Window.alert(param);}

All useful comments are appreciated

Roddy of the Frozen Peas · Accepted Answer · 2012-08-29 21:46:02Z

2

You need to take a reference to this outside the function block:

/**
 * For UI button click method...
 */
private native void test(String param) /*-{
    var theInstance = this;
    var a = ( function b(p) {
        theInstance.@com.(...).TestClass::setTest(Ljava/lang/String;)(p);
    })(param);
}-*/;

private void setTest(String param){
    Window.alert(param);
}

edited Aug 29, 2012 at 21:46

Roddy of the Frozen Peas

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answered May 2, 2012 at 2:21

Manuel Darveau

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Comments

Zasz · Accepted Answer · 2011-07-12 05:06:42Z

1

Your usage of the this keyword may cause the problem. In your context the this keywords points to the closure

(function b(p)
{
 this.@com.(...).TestClass::setTest(Ljava/lang/String;)(p);

})(param);

Ideally it should point to the function that GWT compiles from

private native void test(String param)

this statement.

Try using this code segment (I'm not sure if I got the syntax right, verify with GWT JSNI wiki) :

private native void test(String param)
/*-{    
var a = this.@com.(...).TestClass::setTest(Ljava/lang/String;)(param);    
}-*/

BTW, Having a function whose sole purpose is to call another function is a code smell.

answered Jul 12, 2011 at 5:06

Zasz

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4 Comments

user592704 Over a year ago

Emm I use "this" because all methods are in the same class. I get no compilation error but the Java method invokation works only in the out of the JS function block :( Maybe I do some wrong invokation then? Help me to understand please

Zasz Over a year ago

The problem is the THIS pointer points to a different anonymous class (or prototype) if you use it inside a function block. In order to call GWT functions from javascript the THIS keyword should point to the class generated by GWT. If its too confusing try removing the THIS keyword/qualifier altogether.

user592704 Over a year ago

no method call works within any function block :( I tried to remove "this" but it gave no effect :( So I've still being thinking of... can java method be called right from JS function block or it is useless thing?

Kylos Over a year ago

It's not necessarily a code smell with GWT JSNI. Instead of invoking the wrapper and assigning it to a, the wrapper could instead be assigned to $wnd.test. Then test() could be invoked from pure JS, allowing external JS to call GWT methods.

BenMorel · Accepted Answer · 2013-11-11 23:53:26Z

0

Yes, as Zasz is pointing out, you are overcomplicating your code (expect if you really want to provide a JavaScript method, but in that case you have to do it in a complete different way...)

So I tested the code and this works:

/*    JNI Example method... */
private native void test(String param) /*-{  
    [email protected]._53_JavaScriptOverlayTypes::setTest(Ljava/lang/String;)(param); 
}-*/;

private void setTest(String param){
    Window.alert(param);
}

edited Nov 11, 2013 at 23:53

BenMorel

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answered Jul 12, 2011 at 7:16

Stefan

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1 Comment

user592704 Over a year ago

It's greate but I need to invoke java method right from JS function block and that is the problem I guess :( Is there a optimal way to do so?

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