在异步任务中解析JSON时强制关闭

时间：2012-07-08 14:28:32

标签： android json listview

应用程序在几秒钟后关闭。我可以在logcat中看到JSON值，但结果在listview中没有更新。

我的主要活动类代码如下：

public class MainActivity extends ListActivity {
    private ProgressDialog dialog;
    private static String url="url here";


    private static final String BASE_TAG="base";
    private static final String RATES_TAG="rates";

    JSONParser jParser=new JSONParser();

    ArrayList<HashMap<String,String>> currentRates;

    JSONArray rates=null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        currentRates=new ArrayList<HashMap<String,String>>();

        new getRates().execute();

        ListView lv=getListView();


    }

    public class getRates extends AsyncTask<String,String,String>{

    @Override
    protected void onPreExecute(){
        super.onPreExecute();
        dialog=new ProgressDialog(MainActivity.this);
        dialog.setMessage("Please wait");
        dialog.setIndeterminate(false);
        dialog.setCancelable(false);
        dialog.show();
    }

        @Override
        protected String doInBackground(String... args) {

List<NameValuePair> params=new ArrayList<NameValuePair>();

JSONObject json=jParser.makeHttpRequest(url,"GET",params);

Log.d("Current Rates:",json.toString());

try {
    rates=json.getJSONArray(RATES_TAG);

    for(int i=0;i<rates.length();i++){
        JSONObject c=rates.getJSONObject(i);


        String rates=c.getString(RATES_TAG);

        HashMap<String,String>map=new HashMap<String,String>();

        map.put(RATES_TAG, rates);

        currentRates.add(map);
    }
} catch (JSONException e){
    e.printStackTrace();
}

            return null;
        }

        protected void onPostExecute(String url){
            dialog.dismiss();

            runOnUiThread(new Runnable(){
                public void run(){
                    ListAdapter adapter=new SimpleAdapter(MainActivity.this, currentRates ,R.layout.rates_item,new String[]{RATES_TAG},new int[]{R.id.rates});

                    setListAdapter(adapter);
                }
            });
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }


}

这是我的logcat报告：

> 07-08 19:46:13.103: E/AndroidRuntime(331): FATAL EXCEPTION: AsyncTask
> #1 07-08 19:46:13.103: E/AndroidRuntime(331): java.lang.RuntimeException: An error occured while executing
> doInBackground() 07-08 19:46:13.103: E/AndroidRuntime(331):   at
> android.os.AsyncTask$3.done(AsyncTask.java:200) 07-08 19:46:13.103:
> E/AndroidRuntime(331):    at
> java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> java.util.concurrent.FutureTask.setException(FutureTask.java:125)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> java.util.concurrent.FutureTask.run(FutureTask.java:138) 07-08
> 19:46:13.103: E/AndroidRuntime(331):  at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> java.lang.Thread.run(Thread.java:1019) 07-08 19:46:13.103:
> E/AndroidRuntime(331): Caused by: java.lang.NullPointerException 07-08
> 19:46:13.103: E/AndroidRuntime(331):  at
> com.razzil.currency.MainActivity$getRates.doInBackground(MainActivity.java:69)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> com.razzil.currency.MainActivity$getRates.doInBackground(MainActivity.java:1)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> android.os.AsyncTask$2.call(AsyncTask.java:185) 07-08 19:46:13.103:
> E/AndroidRuntime(331):    at
> java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    ... 4 more 07-08
> 19:46:15.372: E/WindowManager(331): Activity
> com.razzil.currency.MainActivity has leaked window
> com.android.internal.policy.impl.PhoneWindow$DecorView@40520830 that
> was originally added here 07-08 19:46:15.372: E/WindowManager(331):
> android.view.WindowLeaked: Activity com.razzil.currency.MainActivity
> has leaked window
> com.android.internal.policy.impl.PhoneWindow$DecorView@40520830 that
> was originally added here 07-08 19:46:15.372: E/WindowManager(331):
>   at android.view.ViewRoot.<init>(ViewRoot.java:258) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.view.Window$LocalWindowManager.addView(Window.java:424) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> android.app.Dialog.show(Dialog.java:241) 07-08 19:46:15.372:
> E/WindowManager(331):     at
> com.razzil.currency.MainActivity$getRates.onPreExecute(MainActivity.java:59)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.os.AsyncTask.execute(AsyncTask.java:391) 07-08 19:46:15.372:
> E/WindowManager(331):     at
> com.razzil.currency.MainActivity.onCreate(MainActivity.java:43) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.app.ActivityThread.access$1500(ActivityThread.java:117) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> android.os.Handler.dispatchMessage(Handler.java:99) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> android.os.Looper.loop(Looper.java:123) 07-08 19:46:15.372:
> E/WindowManager(331):     at
> android.app.ActivityThread.main(ActivityThread.java:3683) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> java.lang.reflect.Method.invokeNative(Native Method) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> java.lang.reflect.Method.invoke(Method.java:507) 07-08 19:46:15.372:
> E/WindowManager(331):     at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
> 07-08 19:46:15.372: E/WindowManager(331):     at
> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 07-08
> 19:46:15.372: E/WindowManager(331):   at
> dalvik.system.NativeStart.main(Native Method)

1 个答案:

答案 0 :(得分：2)

您正在MainActivity 第69行中点击 NULLPOINTEREXCEPTION 。它在doInBackground方法中。调试它，看看什么值为null并导致问题。 

> java.lang.Thread.run(Thread.java:1019) 07-08 19:46:13.103:
> E/AndroidRuntime(331): Caused by: java.lang.**NullPointerException** 07-08
> 19:46:13.103: E/AndroidRuntime(331):  at
> com.razzil.currency.MainActivity$getRates.doInBackground(MainActivity.java:69)
> 07-08 19:46:13.103: E/AndroidRuntime(331):    at
> com.razzil.currency.MainActivity$getRates.doInBackground(MainActivity.java:1)
> 07-08 19:46:13.103: E/AndroidRuntime(331):
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