空指针json数据

Question

我有一个listview，其特殊 ID 为 @android:id/list

json 数据只有一个包含对象的数组。

public class MainActivity extends ListActivity {

String KEY_DESCRIPT = "DESCRIPTION:";

String KEY_NAME = "NAME:";
String line = null;
JSONArray datalist=null;
JSONObject getobj=null;
BufferedReader br;
StringBuilder sb;
String Web=null;
JSONArray jresult=null;
URL url;
HttpURLConnection cn;
String TAG="MYACTIVITY";
String name = null;
String [] sortedlist;
ProgressBar loading;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    loading= (ProgressBar) findViewById(R.id.progressBar1);
    Web = "http://api.mtgdb.info/search/Dragon";
    new jsonGet().execute(Web);
}

protected class jsonGet extends AsyncTask<String , Void, JSONArray>{

    @Override
    protected JSONArray doInBackground(String... params) {
        try {
            url= new URL(params[0]);
            cn=(HttpURLConnection) url.openConnection();
            br= new BufferedReader(new InputStreamReader(cn.getInputStream()));
            sb= new StringBuilder();
            while((line = br.readLine())!=null){
                sb.append(line+"\n");   
            }
            br.close();



            datalist= new JSONArray(sb.toString());


        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {

            e.printStackTrace();
        }

        return datalist;

    }

    @Override
    protected void onPostExecute(JSONArray result) {
        super.onPostExecute(result);
        jresult=result;
        passList();

        }

    }



public void passList() {
    loading.setVisibility(View.INVISIBLE);
    if (jresult==null){
        Log.e(TAG, "ERROR");

    }else{
        ArrayList<HashMap<String, String>> newlist =new ArrayList<HashMap<String,String>>();

    for (int i =0;i<jresult.length();i++){
        try{
        getobj= jresult.getJSONObject(i);
        name=getobj.getString("name");
        String description =getobj.getString("description");
        HashMap<String, String> secondlist= new HashMap<String, String>();
        secondlist.put(KEY_NAME, name);
        secondlist.put(KEY_DESCRIPT, description);
        newlist.add(secondlist);
        }catch (Exception e){
            Log.i(TAG, "THis error");
        }

    }

    Arrays.sort(sortedlist);

    String [] keys ={KEY_NAME,KEY_DESCRIPT};
    int [] ids ={android.R.id.text1,android.R.id.text2};
    SimpleAdapter adapter = 
            new SimpleAdapter(this, 
                    newlist, android.R.layout.simple_list_item_2, keys, ids);
    setListAdapter(adapter);
    }
}

堆栈跟踪：

1-06 22:49:10.019: D/AndroidRuntime(1476): Shutting down VM
11-06 22:49:10.023: W/dalvikvm(1476): threadid=1: thread exiting with uncaught exception (group=0xa4d50b20)
11-06 22:49:10.023: E/AndroidRuntime(1476): FATAL EXCEPTION: main
11-06 22:49:10.023: E/AndroidRuntime(1476): Process: com.example.mtg, PID: 1476
11-06 22:49:10.023: E/AndroidRuntime(1476): java.lang.NullPointerException
11-06 22:49:10.023: E/AndroidRuntime(1476):     at java.util.ComparableTimSort.sort(ComparableTimSort.java:142)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at java.util.Arrays.sort(Arrays.java:1970)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at com.example.mtg.MainActivity.passList(MainActivity.java:122)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at com.example.mtg.MainActivity$jsonGet.onPostExecute(MainActivity.java:91)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at com.example.mtg.MainActivity$jsonGet.onPostExecute(MainActivity.java:1)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.os.AsyncTask.finish(AsyncTask.java:632)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.os.Handler.dispatchMessage(Handler.java:102)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.os.Looper.loop(Looper.java:136)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at android.app.ActivityThread.main(ActivityThread.java:5001)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at java.lang.reflect.Method.invokeNative(Native Method)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at java.lang.reflect.Method.invoke(Method.java:515)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
11-06 22:49:10.023: E/AndroidRuntime(1476):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您的异常发生在这里：

Arrays.sort(sortedlist);

问题是，您将该变量声明为String [] sortedlist;，但您从未使用数组（即sortedlist = new String[x];）初始化该变量。这意味着sortedlist 仍然是null（这是新对象类型的标准值），这会导致NullPointerException。

检查您为什么从不这样做并更新/修复您的代码。

请注意，禁止将null 元素写入该数组。这意味着，如果您调用Arrays.sort(sortedlist)，数组String[] sortedlist = {"a", null, "b"}; 也会导致NullPointerException。