On 15 sep, 04:24, JaM <[email protected]> wrote:
> I previously posted about Shindig, when probably more appropriately I
> should have posted this question (sorry for the dup).
>
> I have successfully implemented a callback in Java (using an
> interface) which is called from Javascript appropriately, but after
> doing so it seems something is not quite right (perhaps the scope, not
> really sure how to determine). The issue is that I now get an error
> that says something like jV(this.a.a...) and it throws an error saying
> this.a is undefined. The issue only happens when I am trying to
> access instance variables inside my java code. If I do not access
> instance variables everything works fine, which leads me to believe it
> may be a scoping issue. Is there a general rule of thumb for how to
> do this correctly in GWT? Any pointers would be greatly appreciated.
This generally works:
public interface MyCallback {
void callback(int a, int b, String c);
}
public native void doSomething(MyCallback callback) /*-{
$wnd.doSomething(function(a, b, c) {
[email protected]::callback(IILjava/lang/String;)
(a, b, c);
});
}-*/;
Actually, you'd generally call some static method that uses the
UncaughtExceptionHandler if there's one:
public native void doSomething(MyCallback callback) /*-{
$wnd.doSomething(function(a, b, c) {
@my.package.MyClass::callback(Lmy/package/MyCallback;IILjava/
lang/String;)(a, b, c, callback);
});
}-*/;
private static void callback(MyCallback callback, int a, int b, String
c) {
UncaughtExceptionHandler handler = GWT.getUncaughtExceptionHandler
();
if (handler != null) {
callbackImpl(callback, a, b, c);
} else {
callbackAndCatch(handler, callback, a, b, c);
}
}
private static void callbackImpl(MyCallback callback, int a, int b,
String c) {
callback.callback(a, b, c);
}
private static void callbackAndCatch(UncaughtExceptionHandler handler,
MyCallback callback, int a, int b, String c) {
try {
callbackImpl(callback, a, b, c);
} catch (Throwable t) {
handler.onUncaughtException(t);
}
}
..and finally, if your callback is "this":
public native void doSomething() /*-{
var that = this;
$wnd.doSomething(function(a, b, c) {
@my.package.MyClass::callback(Lmy/package/MyCallback;IILjava/lang/
String;)(that, a, b, c);
});
}-*/;
You'll find those patterns several times in GWT itself, as well as in
other GWT libraries wrapping JavaScript libs (GALGWT, GWT-in-the-AIR,
etc.)
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