如何使用 GWT 平台的 UiHandlers？

Question

我一直在尝试写contacts。使用 gwt-platform 的示例我已经使用手动显示成功获得了联系人视图以获取联系人列表，我正在尝试使用 UiHandlers 添加按钮，但它没有在我的 ContactsPresenter 的 onAddButtonClicked() 中调用该方法。

fallowing是我观点的代码sn-p

public class ContactsView extends ViewWithUiHandlers<ContactsViewUiHandlers> implements  ContactsPresenter.MyView {

private final Widget widget;

@UiField
Button addButton;

@UiHandler("addButton")
public void onAddButtonClick(ClickEvent e){
    System.out.println("add button clicked");
    getUiHandlers().onAddButtonClicked();
}  

}

闲置的是UiHandlers接口

public interface ContactsViewUiHandlers extends UiHandlers{
        void onAddButtonClicked();
}

在我的演示者中，我正在使用 onAddButtonClicked() 中的事件总线触发一个事件。

但是我的演示者没有控制，当我单击添加按钮时出现以下异常。

[ERROR] [contactsgwtp] - Uncaught exception escaped

10:17:10.527 [ERROR] [contactsgwtp] 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.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.GeneratedMethodAccessor28.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:662)
Caused by: java.lang.NullPointerException: null
    at com.saik.in.client.core.ContactsView.onAddButtonClick(ContactsView.java:51)
    at com.saik.in.client.core.ContactsView_BinderImpl$1.onClick(ContactsView_BinderImpl.java:50)
    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.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.GeneratedMethodAccessor28.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:662)

关于我所缺少的任何建议，提前感谢

Answer 1

显然getUiHandlers() 是null...但你知道:-)

我预计造成这种情况的原因可能是您在注入关联的演示者（这将是 GWTP 中的正常过程）时忘记设置 UI 处理程序 - 类似于：

public class ContactsPresenter extends Presenter<ContactsPresenter.MyView, ContactsPresenter.MyProxy> 
                               implements ContactsViewUiHandlers 
{
    public interface MyView extends View, HasUiHandlers { /* nothing */ }

    private PlaceManager placeManager;

    @Inject
    ContactsPresenter( final EventBus eventBus , final MyView view , 
                       final MyProxy proxy , final PlaceManager placeManager )
    {
        super( eventBus , view , proxy );
        this.placeManager = placeManager;
        getView().setUiHandlers( this );
    }
    ...

    @Override
    public void onAddButtonClicked()
    {
        placeManager.revealPlace( new PlaceRequest( "somewhereovertheocean" ) );
    }
    ...
}

（操作部分是getView().setUiHandlers( this );和implements ContactsViewUiHandlers）。

顺便说一句，在调用任何方法之前始终检查 getUiHandlers() 是否为空是一种好习惯...

希望对您有所帮助。

干杯，

Answer 2

查看您提供的例外情况，我认为您错过了以下几点：

1. ContactsPresenter 应该像这样实现ContactsViewUiHandlers：ContactsPresenter implemets ContactsViewUiHandlers
2. 将ContactsPresenter 的引用设置为contactsView.UIHandlers，如下所示：getView().setUiHandlers(this);

在做完这两件事之后，你不应该得到提到的异常。希望对您有所帮助。