java - 如何添加复合小部件: This widget's parent does not implement HasWidgets

Question

我不断抛出错误:“这个小部件的父级没有实现 HasWidgets。梳理了网络(包括 stackoverflow)，但无法找出问题所在。我知道将下载对象添加到 VerticalPanel '文本'的方式有问题，但是，我不知道为什么它会抛出它，也不知道如何修复它。此外，当我运行应用程序时，它第一次成功，只在我第二次尝试访问下载页面时抛出错误。任何帮助都会是非常感谢!

public class SIXPAC implements EntryPoint, HasWidgets
{
    private VerticalPanel mainPanel = new VerticalPanel() ;
    private HorizontalPanel menu = new HorizontalPanel() ;
    private VerticalPanel text = new VerticalPanel() ;
    private SIXPACServiceAsync services = GWT.create( SIXPACService.class ) ;

    public void onModuleLoad() 
    {
        header() ;
        changePage( "about.txt" ) ;
        footer() ;

        RootPanel.get( "sixPac" ).add( mainPanel ) ;
        mainPanel.setWidth("100%");
    }

    public void header()
    {
        menu.add( menu stuff... ) ;
        mainPanel.add( menu ) ;
        mainPanel.add( text ) ;
    }

    public void footer()
    {
        mainPanel.add( footer stuff... ) ;
    }

    public void changePage( String token )
    {
            if( token.equals( "download.txt" ) )        // else its download page and need to set up the forms
        {
            text.clear() ;
            try
            {
                add( new Download() ) ;
            }
            catch( Exception e )
            {
                System.out.println( e ) ;
            }
            text.setStyleName( "contentbox" ) ;
        }
    }

    public void add(Widget w) // tried basic implementation of the HasWidgets methods...
    {
        text.add( w ) ;
    }

    public void clear() 
    {

    }

    public Iterator<Widget> iterator() {
        // TODO Auto-generated method stub
        return null;
    }

    public boolean remove(Widget w) {
        // TODO Auto-generated method stub
        return false;
    }
}

对于下载类，为了测试，我基本上删除了所有内容:

package com.sixpac.website.client;

导入java.util.Iterator;

public class Download extends Composite
{
    private static VerticalPanel verticalPanel = new VerticalPanel();

    public Download() 
    {
        verticalPanel.setStyleName("contentbox");
        initWidget( verticalPanel );
        verticalPanel.setWidth("100%");

        verticalPanel.add( new HTML( "<h1>Download</h1>" ) ) ;

        HorizontalPanel horizontalPanel = new HorizontalPanel();
        horizontalPanel.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_CENTER);
        horizontalPanel.setWidth("100%");
        verticalPanel.add( horizontalPanel ) ;

        System.out.println( "creating new login" ) ;
        Login login = new Login() ;
        System.out.println( "creating new register" ) ;
        Register register = new Register() ;

        horizontalPanel.add( login ) ;
        login.setSize("75%", "310px");
        horizontalPanel.setCellVerticalAlignment(login, HasVerticalAlignment.ALIGN_BOTTOM);
        horizontalPanel.add( register ) ;
        register.setSize("90%", "257px");
        horizontalPanel.setCellVerticalAlignment(register, HasVerticalAlignment.ALIGN_BOTTOM);
        setStyleName("gwt");
    }

    public static void downloadOk()
    {
        verticalPanel.add( new HTML( "<br/><br/>" ) ) ;
        verticalPanel.add( new HTML( "<div class=\"contentbox downloadok\">\n\t\n<p>Thank you for downloading SIXPAC Version 0.5 (Beta).</p>\n<p>Please direct all technical questions and bug-reports to Snehit Prabhu (<a href=\"mailto:snehitp@cs.columbia.edu\">snehitp@cs.columbia.edu</a>)</p>\n\t\n<br />\n\t\n<a href=\"#\" class=\"downloadbutton\">Download SIXPAC</a>\n\n<br /><br />\n</div>\n\n\n</div><!--contentbox-->" ) ) ;
    }
}

堆栈跟踪:

    02:24:14.763 [ERROR] [sixpac] Uncaught exception escaped

com.google.gwt.event.shared.UmbrellaException: One or more exceptions caught, see full set in UmbrellaException#getCauses
    at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:129)
    at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129)
    at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116)
    at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177)
    at com.google.gwt.user.client.ui.CustomButton.onBrowserEvent(CustomButton.java:698)
    at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351)
    at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:289)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107)
    at com.google.gwt.dom.client.DOMImplStandard.dispatchEvent(DOMImplStandard.java)
    at com.google.gwt.dom.client.Element$.dispatchEvent$(Element.java:142)
    at com.google.gwt.user.client.ui.CustomButton.onClick(CustomButton.java:825)
    at com.google.gwt.user.client.ui.PushButton.onClick(PushButton.java:190)
    at com.google.gwt.user.client.ui.CustomButton.onBrowserEvent(CustomButton.java:656)
    at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351)
    at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.AssertionError: This UIObject's element is not set; you may be missing a call to either Composite.initWidget() or UIObject.setElement()
    at com.google.gwt.user.client.ui.UIObject.getElement(UIObject.java:527)
    at com.google.gwt.user.client.ui.ComplexPanel.add(ComplexPanel.java:94)
    at com.google.gwt.user.client.ui.VerticalPanel.add(VerticalPanel.java:48)
    at com.sixpac.website.client.SIXPAC.changePage(SIXPAC.java:140)
    at com.sixpac.website.client.SIXPAC$3.onClick(SIXPAC.java:69)
    at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:54)
    at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:1)
    at com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:1)
    at com.google.web.bindery.event.shared.EventBus.dispatchEvent(EventBus.java:40)
    at com.google.web.bindery.event.shared.SimpleEventBus.doFire(SimpleEventBus.java:193)
    at com.google.web.bindery.event.shared.SimpleEventBus.fireEvent(SimpleEventBus.java:88)
    at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:127)
    at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129)
    at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116)
    at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177)
    at com.google.gwt.user.client.ui.CustomButton.onBrowserEvent(CustomButton.java:698)
    at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351)
    at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:289)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107)
    at com.google.gwt.dom.client.DOMImplStandard.dispatchEvent(DOMImplStandard.java)
    at com.google.gwt.dom.client.Element$.dispatchEvent$(Element.java:142)
    at com.google.gwt.user.client.ui.CustomButton.onClick(CustomButton.java:825)
    at com.google.gwt.user.client.ui.PushButton.onClick(PushButton.java:190)
    at com.google.gwt.user.client.ui.CustomButton.onBrowserEvent(CustomButton.java:656)
    at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351)
    at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Thread.java:680)

Answer 1

问题是verticalPanel在下载类中是静态的。我认为这会导致您的代码在多次调用时使用错误的引用来 initWidget 。尝试删除静电它应该可以工作。另外，您可以像实现 add 一样，通过将其传递给文本实例来实现其余的 haswidget 接口(interface)方法。