java - GWT，元素， worker : null instance

Question

使用 GWT 和 elemental，我在 null 实例方面遇到了一些问题。这是代码:

import elemental.events.Event;
import elemental.events.EventListener;
import elemental.html.Window;
import elemental.html.Worker;

public void go()
{
    Window window=elemental.client.Browser.getWindow();
    Worker worker=window.newWorker("task.js");
    EventListener eventListener=new EventListener()
    {
        @Override
        public void handleEvent(Event event)
        {
        }
    }
    System.out.println("worker : "+worker+" eventListener : "+eventListener+" window : "+window);
    worker.setOnmessage(eventListener);
}

显示为:

worker : [object Worker] eventListener : mainpackage.client.MainClass$1@565f81ea window : [object Window]

所以worker不为空，但我在setOnmessage中遇到错误:

com.google.gwt.core.client.JavaScriptException: (String) : Invoking an instance method on a null instance
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.google.gwt.dev.shell.ModuleSpace.createJavaScriptException(ModuleSpace.java:80)
at com.google.gwt.dev.shell.ModuleSpace.createJavaScriptException(ModuleSpace.java:64)
at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:60)
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:576)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:304)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107)
at elemental.js.html.JsWorker$.setOnmessage$(JsWorker.java)
at com.google.gwt.core.client.JavaScriptObject$.elemental_html_Worker_setOnmessage(JavaScriptObject.java)
at mainpackage.client.MainClass.go(MainClass.java:41)
at mainpackage.client.Testthread.onModuleLoad(Testthread.java:30)
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:411)
at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:200)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:526)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
at java.lang.Thread.run(Unknown Source)

为什么会有空实例？我该如何解决这个问题？提前致谢。

Answer 1

com.google.gwt.core.client.JavaScriptException: (String) : Invoking an instance method on a null instance

这一行有一个答案。

当您尝试调用时

worker.setOnmessage(eventListener);

Worker worker=window.newWorker("task.js");

worker 对象为 NULL。

因此，请检查您的 newWorker 方法是否实际上返回 Worker 对象。