Android小部件nullpointexception

Question

我正在使用JSON。我解析了JSON，可以顯示我的JSON列表視圖（圖像和文本），還成功創建了小部件，我想在我的小部件中顯示JSON的第一項標題。我也寫了這段代碼（如果我刪除小部件，然后我可以在小部件中顯示第一個標題），但是一段時間后，當我單擊小部件的按鈕時，我得到了nullPointExcetpion我在做什么錯了？

public class BriWidget extends AppWidgetProvider {
public static String CLOCK_WIDGET_UPDATE = "CLOCK_WIDGET_UPDATE";
RemoteViews remoteViews;
int appWidgetId;
public File file;
public Bitmap bitmap;

@Override
public void onDeleted(Context context, int[] appWidgetIds) {
    Toast.makeText(context, "TimeWidgetRemoved id(s):" + appWidgetIds,
            Toast.LENGTH_SHORT).show();
    super.onDeleted(context, appWidgetIds);
}

@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager,
        int[] appWidgetIds) {
    super.onUpdate(context, appWidgetManager, appWidgetIds);
    ComponentName thisWidget = new ComponentName(context, BriWidget.class);
    for (int widgetId : appWidgetManager.getAppWidgetIds(thisWidget)) {

        Intent intent = new Intent(context, SpleshScreen.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(context, 0,
                intent, 0);
        remoteViews = new RemoteViews(context.getPackageName(),
                R.layout.widget_demo1);
        remoteViews
                .setOnClickPendingIntent(R.id.widgetbtn, pendingIntent);
        remoteViews
                .setOnClickPendingIntent(R.id.widgetImage, pendingIntent);
        remoteViews.setOnClickPendingIntent(R.id.widgetdesc, pendingIntent);
        remoteViews.setOnClickPendingIntent(R.id.widgetbtn,
                buildButtonPendingIntent1(context));
        remoteViews.setTextViewText(R.id.widgetdesc, getDesc());
        appWidgetManager.updateAppWidget(widgetId, remoteViews);
    }
}

@Override
public void onAppWidgetOptionsChanged(Context context,
        AppWidgetManager appWidgetManager, int appWidgetId,
        Bundle newOptions) {

    Toast.makeText(context, "onAppWidgetOptionsChanged() called",
            Toast.LENGTH_SHORT).show();
}

public static PendingIntent buildButtonPendingIntent1(Context context) {

    Intent intent = new Intent();
    intent.setAction(WidgetUtils.WIDGET_UPDATE_ACTION);
    return PendingIntent.getBroadcast(context, 0, intent,
            PendingIntent.FLAG_UPDATE_CURRENT);
}

private static CharSequence getDesc() {
    return "this is a widget example";
}

public static void pushWidgetUpdate(Context context, RemoteViews remoteViews) {
    ComponentName myWidget = new ComponentName(context, BriWidget.class);
    AppWidgetManager manager = AppWidgetManager.getInstance(context);
    manager.updateAppWidget(myWidget, remoteViews);
}

}

public class MyWidgetIntentReceiver extends BroadcastReceiver {



@Override
public void onReceive(Context context, Intent intent) {
    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "YOUR TAG");

    wl.acquire();

    RemoteViews remoteViews = new RemoteViews(context.getPackageName(),
            R.layout.widget_demo1);
    remoteViews.setTextViewText(R.id.widgetdesc, getDesc(""));
    remoteViews.setOnClickPendingIntent(R.id.widgetbtn,
            BriWidget.buildButtonPendingIntent1(context));

    BriWidget
            .pushWidgetUpdate(context.getApplicationContext(), remoteViews);
    ComponentName thiswidget = new ComponentName(context, BriWidget.class);
    AppWidgetManager manager = AppWidgetManager.getInstance(context);
    manager.updateAppWidget(thiswidget, remoteViews);

    wl.release();

}
public void setOnetimeTimer(Context context){
    AlarmManager am=(AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
    Intent intent = new Intent(context, MyWidgetIntentReceiver.class);
    PendingIntent pi = PendingIntent.getBroadcast(context, 0, intent, 0);
    am.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), pi);
}


private String getDesc(String abc) {
    abc = (MainActivity.itemList.get(0).get(MainActivity.KEY_title))
            .toString();

    return abc;
}

}

公共類BRIgeAdapter擴展了BaseAdapter {

Context mContext;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater = null;
public ImageLoader imageLoader;

private int screenSize;

public BRIgeAdapter(Context context, ArrayList<HashMap<String, String>> d,
        int screenSize) {
    this.mContext = context;
    this.data = d;
    this.screenSize = screenSize;
    inflater = (LayoutInflater) mContext
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    imageLoader = new ImageLoader(context.getApplicationContext());
}

public int getCount() {
    return data.size();
}

public Object getItem(int position) {
    return position;
}

public long getItemId(int position) {
    return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
    View vi = convertView;
    if (convertView == null)
        vi = inflater.inflate(R.layout.list_row, null);

    TextView journal = (TextView) vi.findViewById(R.id.smalljournal);
    TextView title = (TextView) vi.findViewById(R.id.smalltitle);
    TextView description = (TextView) vi
            .findViewById(R.id.smallDescription);
    ImageView thumb_image = (ImageView) vi.findViewById(R.id.smallthumb);
    TextView statId = (TextView) vi.findViewById(R.id.smallstatID);
    TextView DateTime = (TextView) vi.findViewById(R.id.smallDateTime);
    HashMap<String, String> itemList = new HashMap<String, String>();
    itemList = data.get(position);

    journal.setText(itemList.get(MainActivity.KEY_journal));
    statId.setText(itemList.get(MainActivity.KEY_statID));


    String titleString = itemList.get(MainActivity.KEY_title);

    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");

    String DateTimeTxt = itemList.get(MainActivity.KEY_pubDate).replace(
            "T", " ");

    try {
        Date _d = df.parse(DateTimeTxt);
        SimpleDateFormat new_df = new SimpleDateFormat("dd.MM.yyyy");
        String _s = new_df.format(_d);
        DateTime.setText(_s);
    } catch (ParseException e) {

        e.printStackTrace();
    }

    if (screenSize == Configuration.SCREENLAYOUT_SIZE_NORMAL)
        description.setVisibility(View.INVISIBLE);

    else
        description.setVisibility(View.VISIBLE);
    title.setText(titleString);

    description.setText(itemList.get(MainActivity.KEY_description));


    String url = itemList.get(MainActivity.KEY_image);

    imageLoader.DisplayImage(url, thumb_image);

    return vi;
}

}

public class MainActivity extends Activity {
public String URL = "***********************";

public static String KEY_title = "title";
public static String KEY_description = "description";
public static String KEY_image = "image";
public static String KEY_journal = "journal";
public static String KEY_JournalID = "JournalID";
public static String KEY_pubDate = "pubDate";
public static String KEY_statID = "statID";
public JSONArray jsonarray;
public ListView list;
public JSONParser jsonparser;
static BRIgeAdapter adapter;

public static ArrayList<HashMap<String, String>> itemList;
public ImageLoader imageLoader;
static final int DIALOG_ERROR_CONNECTION = 1;

private ArrayList<Content> contents = new ArrayList<Content>();

public TransparentProgressDialog pd;
public HashMap<String, String> map;
public Tools tools;

private int screenSize;

public LoadDataAllChanelsToServer loadData;

private ConnectionDetector cd;

@SuppressLint("CutPasteId")
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.main);
    screenSize = getResources().getConfiguration().screenLayout
            & Configuration.SCREENLAYOUT_SIZE_MASK;

    itemList = new ArrayList<HashMap<String, String>>();
    list = (ListView) findViewById(R.id.listView1);
    cd = new ConnectionDetector(getApplicationContext());
    adapter = new BRIgeAdapter(MainActivity.this, itemList, screenSize);

    Thread.setDefaultUncaughtExceptionHandler(new UnCaughtException(this,
            this));
    loadData = new LoadDataAllChanelsToServer();

    pd = new TransparentProgressDialog(this, R.drawable.loader);

    loadData.execute();

}

private class LoadDataAllChanelsToServer extends
        AsyncTask<String, Integer, String> {

    @Override
    protected void onPreExecute() {

        pd.show();
    }

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

        jsonparser = new JSONParser();

        JSONObject jsonobject = jsonparser.getJSONfromURL(URL);
        try {

            jsonarray = jsonobject.getJSONArray("data");

            for (int i = 0; i < jsonarray.length(); i++) {
                jsonobject = jsonarray.getJSONObject(i);

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

                map.put("journal", jsonobject.getString(KEY_journal));
                map.put("image", jsonobject.getString(KEY_image));
                map.put("title", jsonobject.getString(KEY_title));
                map.put("description",
                        jsonobject.getString(KEY_description));
                map.put("JournalID", jsonobject.getString(KEY_JournalID));
                map.put("pubDate", jsonobject.getString(KEY_pubDate));
                map.put("statID", jsonobject.getString(KEY_statID));

                Content cont = new Content(jsonobject.getString("journal"),
                        jsonobject.getString("image"),
                        jsonobject.getString("title"),
                        jsonobject.getString("pubDate"),
                        jsonobject.getString("description"),
                        jsonobject.getString("JournalID"),
                        jsonobject.getString("statID"));
                contents.add(cont);

                itemList.add(map);

            }

        } catch (JSONException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }

        return itemList.toString();

    }

    @Override
    protected void onPostExecute(String result) {
        try {
            if (pd != null) {
                pd.dismiss();

            }
        } catch (Exception e) {

        }

        try {
            adapter = new BRIgeAdapter(MainActivity.this, itemList,
                    screenSize);
            list.setAdapter(adapter);

        } catch (NullPointerException e) {
            e.printStackTrace();
        }

    }

}

}

一段時間后，我在MyWidgetIntentReceiver類getDesc方法中具有nullpointexception abc =（MainActivity.itemList.get（0）.get（MainActivity.KEY_title））.toString（）; 一片空白

Answer 1

在一行中使用這么多的點是不安全的，請嘗試替換

 abc = (MainActivity.itemList.get(0).get(MainActivity.KEY_title))
             .toString();

與：

if (MainActivity.itemList != null && MainActivity.itemList.size() > 0) {

            HashMap<String, String> listItem = MainActivity.itemList.get(0);

            if (listItem != null) {
                adb = listItem.get(MainActivity.KEY_title);
            }
        }

並進行調試以找出哪個對象為NULL。

順便說一句，在Activity中使用靜態ArrayList對象是個壞主意，Activity的靜態數據將由系統GC清除，請使用startActivityForResult（）從Activity中獲取數據。