android的两个片段asynctask类nullpointexception

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我有两个片段在我的tabhost（viewpager）和我解析的json，我可以显示jsons的项目在listview每个片段，不同的是只有json的url.first时间两个Asynctask类运行同一时间但现在我写了setMenuVisibility方法，现在我可以加载Asynctask类，当我想要。例如，如果我去第二个片段，第二个Asynctask类运行，但是当我回去第一个活动（meybe再去第二个片段）时，我有nullpoinexception。这是我的代码，如果有人知道的解决方案，请帮助我感谢这是我Mainactivity.java类代码android的两个片段asynctask类nullpointexception

public class MainActivity extends FragmentActivity implements 
    TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener { 

private TabHost mTabHost; 
private ViewPager mViewPager; 
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, MainActivity.TabInfo>(); 
private PagerAdapter mPagerAdapter; 
private HorizontalScrollView horizontalScrollView; 
private ImageButton menubutton; 

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    requestWindowFeature(Window.FEATURE_NO_TITLE); 
    setContentView(R.layout.activity_main); 
    menubutton = (ImageButton) findViewById(R.id.menubutton); 
    menubutton.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View arg0) { 
      Toast.makeText(getApplicationContext(), "Helo", 
        Toast.LENGTH_SHORT).show(); 

     } 
    }); 

    this.initialiseTabHost(savedInstanceState); 
    if (savedInstanceState != null) { 
     mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab")); 
    } 

    this.intialiseViewPager(); 
} 

protected void onSaveInstanceState(Bundle outState) { 
    outState.putString("tab", mTabHost.getCurrentTabTag()); 
    super.onSaveInstanceState(outState); 
} 

private void intialiseViewPager() { 

    List<Fragment> fragments = new Vector<Fragment>(); 
    fragments.add(Fragment.instantiate(this, Pirveli.class.getName())); 
    fragments.add(Fragment.instantiate(this, Meore.class.getName())); 


    this.mPagerAdapter = new PagerAdapter(
      super.getSupportFragmentManager(), fragments); 
    // 
    this.mViewPager = (ViewPager) super.findViewById(R.id.viewpager); 
    this.horizontalScrollView = (HorizontalScrollView) super 
      .findViewById(R.id.horizontalScrollView); 
    this.mViewPager.setAdapter(this.mPagerAdapter); 
    this.mViewPager.setOnPageChangeListener(this); 
} 

public void centerTabItem(int position) { 
    mTabHost.setCurrentTab(position); 
    final TabWidget tabWidget = mTabHost.getTabWidget(); 
    final int screenWidth = getWindowManager().getDefaultDisplay() 
      .getWidth(); 
    final int leftX = tabWidget.getChildAt(position).getLeft(); 
    int newX = 0; 

    newX = leftX + (tabWidget.getChildAt(position).getWidth()/2) 
      - (screenWidth/2); 
    if (newX < 0) { 
     newX = 0; 
    } 
    horizontalScrollView.scrollTo(newX, 0); 
} 

private void initialiseTabHost(Bundle args) { 
    mTabHost = (TabHost) findViewById(android.R.id.tabhost); 
    mTabHost.setup(); 
    TabInfo tabInfo = null; 
    MainActivity.AddTab(
      this, 
      this.mTabHost, 
      this.mTabHost.newTabSpec("All Channels").setIndicator(
        "All Channels"), (tabInfo = new TabInfo("All Channels", 
        Pirveli.class, args))); 
    this.mapTabInfo.put(tabInfo.tag, tabInfo); 

    MainActivity.AddTab(
      this, 
      this.mTabHost, 
      this.mTabHost.newTabSpec("Commersant").setIndicator(
        "Commersant"), (tabInfo = new TabInfo("Commersant", 
        Meore.class, args))); 



    mTabHost.setOnTabChangedListener(this); 
} 

private static void AddTab(MainActivity activity, TabHost tabHost, 
     TabHost.TabSpec tabSpec, TabInfo tabInfo) { 

    tabSpec.setContent(activity.new TabFactory(activity)); 
    tabHost.addTab(tabSpec); 
} 

public void onTabChanged(String tag) { 

    int pos = this.mTabHost.getCurrentTab(); 
    this.mViewPager.setCurrentItem(pos); 
} 

@Override 
public void onPageScrolled(int position, float positionOffset, 
     int positionOffsetPixels) { 

} 

@Override 
public void onPageSelected(int position) { 

    centerTabItem(position); 
} 

@Override 
public void onPageScrollStateChanged(int state) { 

} 

private class TabInfo { 
    private String tag; 
    private Class<?> clss; 
    private Bundle args; 
    private Fragment fragment; 

    TabInfo(String tag, Class<?> clazz, Bundle args) { 
     this.tag = tag; 
     this.clss = clazz; 
     this.args = args; 
    } 

} 

class TabFactory implements TabContentFactory { 

    private final Context mContext; 

    public TabFactory(Context context) { 
     mContext = context; 
    } 

    public View createTabContent(String tag) { 
     View v = new View(mContext); 
     v.setMinimumWidth(0); 
     v.setMinimumHeight(0); 
     return v; 
    } 

}

}

这是我的第一个片段码

public class Pirveli extends Fragment { 
private 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 DealBoxAdapter adapter; 
ProgressDialog pDialog, pDialog1; 

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

private int screenSize; 
private LoadDataAllChanelsToServer loader; 
public static String dateTime; 

public TextView journal, tittle, description, smalllink, DateTime, 
     smallstatID; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 

    View rootView = inflater.inflate(R.layout.send_items, container, false); 
    list = (ListView) rootView.findViewById(R.id.pirvelilistview); 

    // pd = new TransparentProgressDialog(getActivity(), R.drawable.loader); 
    screenSize = getResources().getConfiguration().screenLayout 
      & Configuration.SCREENLAYOUT_SIZE_MASK; 
    loader = new LoadDataAllChanelsToServer(); 
    loader.execute(); 

    return rootView; 
} 

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

    @Override 
    protected void onPreExecute() { 

     pDialog = new ProgressDialog(getActivity()); 
     pDialog.setMessage("Authenticating user..."); 
     pDialog.show(); 
     // 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); 

       HashMap<String, String> 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)); 

       itemList.add(map); 
       dateTime = itemList.get(itemList.size() - 1).get(
         KEY_pubDate); 

      } 

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

     return itemList.toString(); 

    } 

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

      } 
     } catch (Exception e) { 

     } 

     try { 
      adapter = new DealBoxAdapter(getActivity(), itemList, 
        screenSize); 
      adapter.notifyDataSetChanged(); 
      list.setAdapter(adapter); 

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

    } 

} 

@Override 
public void onDestroy() { 
    super.onDestroy(); 
    try { 
     if (loader != null) { 
      loader.cancel(true); 
      loader = null; 
     } 
    } catch (Exception e) { 

    } 

}

} 和第二个片段的代码

public class Meore extends Fragment { 
private 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 TransparentProgressDialog pd; 
public JSONParser jsonparser; 
static DealBoxAdapter adapter; 
ProgressDialog pDialog, pDialog1; 

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


private int screenSize; 

LoadDataAllChanelsToServer1 load; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 

    View rootView = inflater.inflate(R.layout.recived_items, container, 
      false); 
    list = (ListView) rootView.findViewById(R.id.listView2); 
    pd = new TransparentProgressDialog(getActivity(), R.drawable.loader); 
    screenSize = getResources().getConfiguration().screenLayout 
      & Configuration.SCREENLAYOUT_SIZE_MASK; 
    load = new LoadDataAllChanelsToServer1(); 
    return rootView; 
} 

private class LoadDataAllChanelsToServer1 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); 

       HashMap<String, String> 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)); 

       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 DealBoxAdapter(getActivity(), itemList, 
        screenSize); 
      list.setAdapter(adapter); 

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

    } 

} 

@Override 
public void setMenuVisibility(final boolean visible) { 
    super.setMenuVisibility(visible); 
    if (visible) { 
     load.execute(); 
    } 
} 

@Override 
public void onDestroy() { 
    super.onDestroy(); 
    try { 
     if (load != null) { 
      load.cancel(true); 
      load = null; 
     } 
    } catch (Exception e) { 

    } 

}

} 我logcat的错误是：java.lang.illegalStateException：不能执行任务：

if (visible) { 
    new LoadDataAllChanelsToServer1().execute(); 
    //load.execute(); 
}

代替：任务已经（在第二个片段的setMenuVisibility法）

来源

2014-02-19 user3293990

后堆栈跟踪 – Raghunandan

（IllegalStateException异常不能执行任务的任务已经运行），这是第二个片段的setMenuVisibility方法的错误 – user3293990

试试这个代码执行：

if (visible) { 
    load.execute(); 
}

来源

2014-02-19 10:37:46

我tryed，但我也有相同的错误 – user3293990

可以请发布完整的logcat错误.. –

是的确定这是我的logcat图片错误（http://postimg.org/image/cwunwdpp9/full/）请看看我的图片 – user3293990

android的两个片段asynctask类nullpointexception

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