我被困在GWT SimpleEventbus的這個簡單實現上數小時。Nullpointer [傘]從Singleton發射GWT SimpleEventBus事件時發生異常
這個設置有什麼問題嗎?這可能是什麼原因?
我使用的Eventbus在我的入口點類initalized的web.binderyEventbus
import com.google.web.bindery.event.shared.SimpleEventBus;
。
public void onModuleLoad() {
ApplicationEvents = new SimpleEventBus();
然後它被注入到Singleton LoadData和MainView(UIBinder類沒有MVP)中。
LoadData.initLoadData(ApplicationEvents);
view = new MainView(ApplicationEvents);
initLoadData基本上是構造函數的別名,只是它沒有返回任何東西。
public class LoadData {
private final SimpleEventBus eventBus;
private LoadData(final SimpleEventBus bus) {
eventBus = bus;
...
}
public static void initLoadData(final SimpleEventBus bus){
if (instance == null){
instance = new LoadData(bus);
}
}
事件總線被這樣注入到MainView中。
public class MainView extends Composite {
private final SimpleEventBus eventbus;
public MainView(final SimpleEventBus bus) {
eventbus = bus;
...
然後處理程序被註冊。
eventbus.addHandler(EntriesReceiveEvent.TYPE, new EntriesReceiveEventHandler() {
@Override
public void onEntriesReceive(EntriesReceiveEvent event) {
...
}
});
而在該方法的末尾,我調用LoadData中的方法。
LoadData.getLoadData().fetchYears(); //alias for loadIndex
的loadIndex方法LoadData.java
private void loadIndex() {
System.out.println(eventBus.toString());
if(indexEntries == null){
AsyncCallback..
public void onSuccess(Map<Short, IndexEntry> result) {
eventBus.fireEvent(new EntriesReceiveEvent());
//^^ LoadData.java:190
EntriesReceiveEvent.java
import com.google.gwt.event.shared.GwtEvent;
public class EntriesReceiveEvent extends GwtEvent<EntriesReceiveEventHandler> {
public static Type<EntriesReceiveEventHandler> TYPE =
new Type<EntriesReceiveEventHandler>();
@Override
public Type<EntriesReceiveEventHandler> getAssociatedType() {
return TYPE;
}
@Override
protected void dispatch(EntriesReceiveEventHandler handler) {
handler.onEntriesReceive(this);
}
}
而且它的處理器EntriesReceiveEventHandler.java
import com.google.gwt.event.shared.EventHandler;
public interface EntriesReceiveEventHandler extends EventHandler {
void onEntriesReceive(EntriesReceiveEvent event);
}
最後是例外。
11:36:57.417 [ERROR] [] Uncaught exception escaped
com.google.web.bindery.event.shared.UmbrellaException: Exception caught: null
at com.google.web.bindery.event.shared.SimpleEventBus.doFire(SimpleEventBus.java:203)
at com.google.web.bindery.event.shared.SimpleEventBus.fireEvent(SimpleEventBus.java:88)
at com.SoftwareEngineering.client.LoadData$2.onSuccess(LoadData.java:190)
at com.SoftwareEngineering.client.LoadData$2.onSuccess(LoadData.java:1)
at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:232)
at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:258)
at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:412)
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.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:338)
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219)
at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279)
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:242)
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.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:293)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
at java.lang.Thread.run(Unknown Source)
我認爲Eventbus可能不一樣,我不知道,如果他們都在談論同樣的Eventbus。然而,證明我的擔憂是錯誤的。
旁邊的問題:你認爲Singleton在這方面bad?這是一個相當小的項目,處理所有RPC請求的LoadData需要全局可用。
謝謝你的幫助!
太棒了!就是這樣!我知道在事件處理程序中調用的函數並不穩定,但我不認爲這是一個問題。我想讓Eventbus先運行...非常感謝! 我不知道UmbreallaException的含義。對於任何人不知道這一點:http://stackoverflow.com/questions/8362613/why-does-umbrellaexception-have-that-name – Patrick