using Window.alert() in a playn project

Question

Just for testing I tried to use the Window.alert() function from the com.google.gwt.user.client.Window package in my playn project. But when I try to run the programm I got an Error Message like this:

"Caused by: java.lang.UnsupportedOperationException: ERROR: GWT.create() is only usable in client code! It cannot be called, for example, from server code. If you are running a unit test, check that your test case extends GWTTestCase and that GWT.create() is not called from within an initializer or constructor. "

I really do not understand it. In my playn project is only client side code in use. So what's the problem?

can you provide the code snippet? Window.alert never made any problems for me, so I'm courious... — Stefan, May 25 '12 at 12:11
Update: It works fine as a Web Application, but not as a Java Application. — Rock Solid, May 25 '12 at 22:43

score 0 · Answer 1 · edited May 23 '17 at 11:56

GWT.create() is currently supported in pure java in gwt trunk. I am using it in a playn project myself {albeit with a slight glitch: Force GWT compiler to stop pruning invalid CompilationUnits }.

If you download and build trunk, you will be able to circumvent GWT.create() issues by registering ClassInstantiators for whatever class is causing your errors. In this case, the Window class has a static instance of WindowImpl that is throwing this error when jvm hits the Window class. If you register a ClassInstantiator for WindowImpl, this will not happen. Unfortunately, the Window.alert method goes straight to native js, so it may still bomb out on you.

If you don't know how / want to build gwt from trunk, ping me an email and I can send you the jars. If you still have problems with .alert() being a native method, let me know, and I will create a custom trunk build that defers .alert() into the WindowImpl singleton, so you can have it do something meaningful, like popup an alert message ;-}

If you feel adventurous, download gwt trunk, go into Window, copy the static alert method into an instance-level method on WindowImpl, make the original method delegate to WindowImpl, and then in your java code, call ServerGwtBridge.register(WindowImpl.class, new ClassInstantiator(){...}), and return whatever implementation you want for .alert() in java and android.

Of course, it would probably be easier to just register a delegate service that is different for each build, and have gwt call Window.alert() while java or android popup a widget. You would then have to run your calls to alert through the delegate, but it saves you the trouble of hacking against trunk. — Ajax, May 31 '12 at 16:04

using Window.alert() in a playn project

1 Answers1