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();

在数据类中我已经：

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出现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)

我看不出问题出在哪里。

谢谢：）

Answer 1

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<String>();
}

Answer 2

在AsyncTask中，您需要初始化引用字段，如下所示：

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

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<String> citations = new ArrayList<String>();



@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;
     }   
}

另外两件事：

java中的标准约定说类名应始终以大写字母开头。请考虑将您的AsyncTask类名称更改为类似于DataTask的内容，它既符合约定，又更具体于类的功能。
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。

致命异常：AsyncTask＃1

2 个答案: