从GWT JSNI调用Java方法

Question

First, yes I have searched already and found this answer already:

GWT JSNI - problem passing Strings

I'm trying to call a java method from a JSNI method, but not getting anywhere. I've tried the advice given above, but it still won't work.

Here's the code:

public native void initCustomListeners(MapmakerMapViewPresenter.MyView view) /*-{
//public native void initCustomListeners() /*-{

    $wnd.getLocationDescriptions = function(lng, lat) {
        $entry(view.@org.jason.mapmaker.client.view.MapmakerMapViewImpl::getLocationDescriptions(DD)(lng, lat));
    }

    $wnd.google.maps.event.addListener(map, 'click', function(event) {
        var lat = event.latLng.lat().toFixed(3);
        var lng = event.latLng.lng().toFixed(3);
        alert("(" + lat + ", " + lng + ")");
        $wnd.getLocationDescriptions(lng, lat);

        alert("Test!");
    });
}-*/;    @Override
public void getLocationDescriptions(double lng, double lat) {
    getUiHandlers().doGetLocationDescriptions(lng, lat);
}

Can anyone help me out?

Jason

Answer 1

I don't know if that's the issue (you don't even say how that code behaves vs. how you expect it to behave) but there are a few bugs in your code:

• $entry wraps a function, so you have to call the function it returns, rather than (uselessly) wrap the result of the function after calling it! Ie $entry(function(lat,lng) { foo.@bar.Baz::quux(DD)(a, b); } rather than $entry(foo.@bar.Baz::quux(DD)(a, b))

• you addListener on a map but that variable is never defined.

Answer 2

One mistake I can see is that you should do:

$wnd.getLocationDescriptions = $entry(@org.jason.mapmaker.client.view.MapmakerMapViewImpl::getLocationDescriptions(DD)(lng, lat));

(not with the function 'wrapper' you use), and then call the function from javascript via:

$wnd.getLocationDescriptions(lng, lat);

Also, the 'that' variable is not necessary (or 'this'), before the @. I'm also not sure about the $wnd.google.maps.event.addListener( thing, are you sure there's such an object assigned on $wnd?

Last, take one more look at this:

https://developers.google.com/web-toolkit/doc/latest/DevGuideCodingBasicsJSNI

Answer 3

I'm still missing something, and I've stared at the given code for quite awhile.

Here's the current version of the code:

public native void initCustomListeners(JavaScriptObject map) /*-{

    var that = this;

    $wnd.getLocationDescriptions = function(lng, lat) {
        $entry(that.@org.jason.mapmaker.client.presenter.MapmakerMapViewPresenter::doGetLocationDescriptions(DD))(lng,lat);
    }

    $wnd.google.maps.event.addListener(map, 'click', function(event) {
        var lat = event.latLng.lat();
        var lng = event.latLng.lng();
        alert("(" + lat + ", " + lng + ")");
        @com.google.gwt.core.client.GWT::log(Ljava/lang/String;)("calling $wnd.getLocationDescriptions()");
        $wnd.getLocationDescriptions(lng, lat);
        @com.google.gwt.core.client.GWT::log(Ljava/lang/String;)("called $wnd.getLocationDescriptions()");
    });
}-*/;

The call is resulting in a ClassCastException. Sorry if I've missed something that should be obvious.