致命exception：AsyncTask＃1
我想使用AsynTask来解析XML数据。 所以在我的活动中：
static List citations = null; static void setCitations(List data) { citations = data; } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); new data().execute(); 在数据类中我有：
class data extends AsyncTask<Void, Void, List> { private XMLReader saxReader; private SimpleContentHandler simpleContentHandler; private List citations; @Override protected void onPreExecute() { Log.i("AsyncTask", "onPreExecute"); } @Override public void onPostExecute(List citations) { GuiguiActivity.setCitations(citations); } @Override protected List doInBackground(Void... params) { citations.add("TEST 1");citations.add("TEST 2"); return citations; } }
而不是citations.add我是我的XML解析器，但即使在这种情况下也会发生citations.add错误。
10-24 15:28:46.647: E/AndroidRuntime(1160): FATAL EXCEPTION: AsyncTask #1 10-24 15:28:46.647: E/AndroidRuntime(1160): java.lang.RuntimeException: An error occured while executing doInBackground() 10-24 15:28:46.647: E/AndroidRuntime(1160): at android.os.AsyncTask$3.done(AsyncTask.java:278) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask.setException(FutureTask.java:124) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask.run(FutureTask.java:137) 10-24 15:28:46.647: E/AndroidRuntime(1160): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.lang.Thread.run(Thread.java:856) 10-24 15:28:46.647: E/AndroidRuntime(1160): Caused by: java.lang.NullPointerException 10-24 15:28:46.647: E/AndroidRuntime(1160): at guigui.first.project.data.doInBackground(data.java:82) 10-24 15:28:46.647: E/AndroidRuntime(1160): at guigui.first.project.data.doInBackground(data.java:1) 10-24 15:28:46.647: E/AndroidRuntime(1160): at android.os.AsyncTask$2.call(AsyncTask.java:264) 10-24 15:28:46.647: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
我不知道问题出在哪里。
谢谢 ：）
您没有初始化citations字段。 像这样在data类中添加一个构造函数：
public data(){ citations = new ArrayList(); }
在您的AsyncTask中，您需要初始化引用字段，如下所示：
class data extends AsyncTask> { private XMLReader saxReader; private SimpleContentHandler simpleContentHandler; //I chose and array list here as a concrete implmentation. But you could use any other //class that also implements the List interface if you want to. private List citations = new ArrayList (); @Override protected void onPreExecute() { Log.i("AsyncTask", "onPreExecute"); } @Override public void onPostExecute(List citations) { GuiguiActivity.setCitations(citations); } @Override protected List doInBackground(Void... params) { citations.add("TEST 1");citations.add("TEST 2"); return citations; } }
另外两件事：
- java中的标准约定说类名应该始终以大写字母开头。 考虑将您的AsyncTask类名称更改为类似于DataTask的内容，它既符合约定，又更具体于类的function。
- 你有很多变量都有相似的名字。 您应该尝试清除每个实际意味着什么，并为所有变量赋予更多有意义的名称。 这有助于防止进一步混淆。