Question

I’m tryin to debug an existing app with some sort of login page already designed. However, when I go to ‘Run as Java application’ in Eclipse I receive an error:

01:18:30.207 [ERROR] [pzflex_test] Unable to load module entry point class com.wai.pzflex.client.PZFlex_Test (see associated exception for details)
java.lang.AssertionError: null
    at com.google.gwt.user.client.ui.TextBox.wrap(TextBox.java:63)
    at com.wai.pzflex.client.PZFlex_Test.onModuleLoad(PZFlex_Test.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:396)
    at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:200)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:525)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Unknown Source)

Here is the code that I’m trying to debug using Eclipse.

public void onModuleLoad() 
    {
        try
        {
        HTMLPanel panel = new HTMLPanel("<table align='center'><tr>" + 
            "<td colspan='2' style='font-weight:bold;'>Please enter your username and password:</td>" +
            "</tr><tr><td>Username: </td><td><input type='text' id='loginuser'></td></tr>" +
            "<tr><td>Password: </td><td><input type='password' id='loginpass'></td></tr>" +
            "<tr><td colspan='2' align='right'><button id='loginbutton'>Login</button></td>" +
            "</tr></table>");

        //final - entity that cannot be changed later
        final TextBox username = TextBox.wrap(panel.getElementById("loginuser"));
        final TextBox pass = TextBox.wrap(panel.getElementById("loginpass"));

        RootPanel.get("content").add(panel);

The application seems to runs up until the ‘final Textbox..’ line of code but when I press resume, I get the errors.

The odd thing is that I can do a GWT Compile and the login page seems to load fine. I don’t understand why this happens just when I go to debug it.

Again I am new to Java and the whole GWT/GAE so any advice would be greatly appreciated.

Answer 1

Look at what the failing assertion is:

public static TextBox wrap(Element element) {
  // Assert that the element is attached.
  assert Document.get().getBody().isOrHasChild(element);

(source: https://code.google.com/p/google-web-toolkit/source/browse/tags/2.5.0/user/src/com/google/gwt/user/client/ui/TextBox.java#61 )

This means you’d need to RootPanel.get("content").add(panel); before you TextBox.wrap().

Except that it won’t work either. It’ll fail later because the wrapped element is within a widget (the HTMLPanel).

What you need to do is remove the <input> from the HTML string and add IDs to the <td>, build your TextBox and PasswordBox like regular widgets, and then use add(Widget,String) to put them in the <td>s in the HTMLPanel.

Depending on what you need to do, maybe you don’t need the <input>s as widgets though, in which case, just use getElementById on the HTMLPanel and possible cast() the result to an InputElement.