Question

***我试图显示一个填充了图像和文本的列表，当我从UI构建器渲染res文件时，我得到空指针异常。以下是代码：
@Override

protected void beforeMain（Form f）{

super.beforeMain(f);
   final List list = findList(f);
   Component selected = createContainer(fetchResourceFile(), "Renderer");
   Component unselected = createContainer(fetchResourceFile(), "Renderer");
   System.out.println(selected.getName());
   list.setRenderer(new GenericListCellRenderer(selected, unselected) {
      public Component getListCellRendererComponent(List list, Object value, int index, boolean isSelected) {
         if ((index + 1) >= list.size()) {
            fetchMore(list);
         }
         return super.getListCellRendererComponent(list, value, index, isSelected);
      }

        private void fetchMore(final List list) {
            // TODO Auto-generated method stub


            // TODO Auto-generated method stub
            NetworkManager networkManager = NetworkManager.getInstance();
            networkManager.start();
            networkManager.addErrorListener(new ActionListener() {
             public void actionPerformed(ActionEvent evt) {
             NetworkEvent n = (NetworkEvent) evt;
                n.getError().printStackTrace();                        
             }});   

            ConnectionRequest request = new ConnectionRequest() {

                String array[] ;
                String images[];
                //StringBuffer sb = new StringBuffer();  
                Hashtable h;
                Vector tweets;
               // @Override
                protected void postResponse() {

                    //cmp.setModel(new com.codename1.ui.list.DefaultListModel(array));


                }
                protected void readResponse(InputStream input) throws IOException {


                    Result result = Result.fromContent(input, Result.XML);


                     array = result.getAsStringArray("/music[1]//thumb_url");

                     int count = list.size();

                     for (int i = 0; i < array.length; i++) {
                           // Hashtable tweet = (Hashtable)tweets.elementAt(i);
                            list.addItem(array[i]);
                            addAvatar(list, array[i], count + i);
                         }
                    System.out.println(""+array.length);


                }  
                private void addAvatar(List list, String array, int i) {
                    // TODO Auto-generated method stub


                    //String url = (String)array.get("profile_image_url");
                    //String user = (String)array.get("from_user");
                   // if (array == null || array.startsWith("http:") == false) {
                       // ImageDownloadService doesn't support HTTPS at moment
                     //  return;
                    //}
                    ImageDownloadService ids = new ImageDownloadService(array, list, i, "avatar");
                    ids.setDuplicateSupported(true);
                    NetworkManager.getInstance().addToQueue(ids);
                    ImageDownloadService.createImageToStorage(array, list, i, "avatar", "-avatar",
                         new Dimension(48, 48));



                }

                protected void handleException(Exception err) {
                     //An error occured - show a message:
           Dialog.show("Alert", "Are you connected to the internet? Check your connection", "Ok", null);
               }
            };
            request.setUrl("http://api.androidhive.info/music/music.xml");    //servlet calling
            request.setPost(false);
            //infiniteProgress prog=
            InfiniteProgress prog=new InfiniteProgress();
            Dialog dlg=prog.showInifiniteBlocking();
            request.setDisposeOnCompletion(dlg);
            networkManager.addToQueueAndWait(request);
                        }


   });    }

以下是异常通过在sun.reflect.NativeMethodAccessorImpl.invoke0（本机方法）下的sun.reflect.NativeMethodAccessorImpl.invoke（未知来源）的java.lang.reflect.InvocationTargetException，位于java.lang.reflect的sun.reflect.DelegatingMethodAccessorImpl.invoke（未知来源）。在com.codename1.impl.javase.Executor $ 1.run（Executor.java:95）的com.codename1.ui.Display.processSerialCalls（Display.java:1075）的com.codename1.ui上的Method.invoke（未知来源） com.codename1.ui.RunnableWrapper.run（RunnableWrapper.java:120）中的.Display.mainEDTLoop（Display.java:897）at com.codename1.impl.CodenameOneThread.run（CodenameOneThread.java:176）引起： java.lang.NullPointerException at userclasses.StateMachine.beforeMain（StateMachine.java:117) at generated.StateMachineBase.beforeShow（StateMachineBase.java:218）at com.codename1.ui.util.UIBuilder.showForm（UIBuilder） .java：2436）at com.codename1.ui.util.UIBuilder.showForm（UIBuilder.java:2 483）在generate.StateMachineBase（StateMachineBase.java:31）的generated.StateMachineBase.startApp（StateMachineBase.java:57）at user.StateMachineBase。（StateMachineBase.java:100）at userclasses.StateMachine。（StateMachine.java:38 ）在com.prime.cnna.MyApplication.start（MyApplication.java:62）
空指针跟随行的异常 list.setRenderer（new GenericListCellRenderer（selected，unselected）{ }）; * 的

Answer 1

在不突出显示实际行117的情况下指定异常并不是很有帮助。

您正在从渲染器执行网络请求，这可能不是一个好方法，每分钟会被调用数千次。您应该使用该模型来实现延迟数据提取，例如https://code.google.com/p/codenameone/source/browse/trunk/CodenameOne/src/com/codename1/cloud/CloudListModel.java

渲染genericlistrenderer时出现空指针异常

1 个答案: