致命异常:AsyncTask#1

Question

我想使用AsynTask来解析XML数据.所以在我的活动中:

static List<String> citations = null;

    static void setCitations(List<String> 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:

class data extends AsyncTask<Void, Void, List<String>> {

    private XMLReader saxReader;
    private SimpleContentHandler simpleContentHandler;

    private List<String> citations;

    @Override
    protected void onPreExecute() {
        Log.i("AsyncTask", "onPreExecute");
    }

    @Override
    public void onPostExecute(List<String> citations) {
        GuiguiActivity.setCitations(citations);
    }


    @Override
    protected List<String> 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 :)

Answer 1

你没有初始化citations字段.data像这样在你的类中添加一个构造函数:

public data(){
    citations = new ArrayList<String>();
}