空指针异常ListView中

当无线网络是 - 所有的作品，但是当它关闭 - 我得到空指针异常空指针异常ListView中

package ua.khuta.myskidka; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.database.Cursor; 
import android.graphics.Color; 
import android.net.ConnectivityManager; 
import android.net.NetworkInfo; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 

import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ListView; 

public class FragmentNews extends Fragment { 
private View v; 
ListView lvNews; 
Database db; 
mySCadapter scAdapter; 
public String DEBUG_TAG = "myLogs"; 
String[] from = new String[] { Database.NEWS_TITLE, Database.NEWS_IMAGE_URL, 
     Database.NEWS_SHORT_DESCRIPTION }; 
int [] to = new int[] { R.id.item_news_tv_title, R.id.item_news_iv_image, 
     R.id.item_news_tv_short_description }; 



@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 
    v = inflater.inflate(R.layout.fragment_news, null); 
    lvNews = (ListView) v.findViewById(R.id.lv_new); 
    lvNews.setCacheColorHint(Color.TRANSPARENT); 

    return v; 
} 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    db = Database.getInstance(getActivity()); 

    ConnectivityManager connManager = (ConnectivityManager) getActivity() 
      .getSystemService(getActivity().CONNECTIVITY_SERVICE); 
    NetworkInfo mWifi = connManager 
      .getNetworkInfo(ConnectivityManager.TYPE_WIFI); 

    if (mWifi.isConnected()) { 
     Log.d(DEBUG_TAG, "wi-fi is on"); 
     db.cleanDB(); 
     GetJSON getJSON = new GetJSON(); 
     getJSON.execute(); 
    } else { 

     Log.d(DEBUG_TAG, "wi-fi is off"); 

     Cursor c = db.getNewsFromDb(); 
     Log.d(DEBUG_TAG, String.valueOf(c.getCount())); 
     mySCadapter scAdapter = new mySCadapter(getActivity(), R.layout.item_news, c, 
       from, to); 

     lvNews.setAdapter(scAdapter); 
    } 

} 



class GetJSON extends AsyncTask<Void, Void, Void> { 

    @Override 
    protected Void doInBackground(Void... params) { 
     // Creating JSON Parser instance 

     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 

     Cursor c = db.getNewsFromDb(); 
     scAdapter = new mySCadapter(getActivity(), R.layout.item_news, c, 
       from, to); 

     lvNews.setAdapter(scAdapter); 

     super.onPostExecute(result); 
    } 

} 

}

错误日志

10-10 09:12:53.275: E/AndroidRuntime(28582): FATAL EXCEPTION: main 
10-10 09:12:53.275: E/AndroidRuntime(28582): java.lang.RuntimeException: Unable to start activity ComponentInfo{ua.khuta.myskidka/ua.khuta.myskidka.MainActivity}: java.lang.NullPointerException 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.os.Looper.loop(Looper.java:137) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread.main(ActivityThread.java:5103) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at java.lang.reflect.Method.invokeNative(Native Method) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at java.lang.reflect.Method.invoke(Method.java:525) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at dalvik.system.NativeStart.main(Native Method) 
10-10 09:12:53.275: E/AndroidRuntime(28582): Caused by: java.lang.NullPointerException 
10-10 09:12:53.275: E/AndroidRuntime(28582): at ua.khuta.myskidka.FragmentNews.onCreate(FragmentNews.java:82) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.Fragment.performCreate(Fragment.java:1455) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:893) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:556) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.Activity.performStart(Activity.java:5143) 
10-10 09:12:53.275: E/AndroidRuntime(28582): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184) 
10-10 09:12:53.275: E/AndroidRuntime(28582): ... 11 more

来源

2013-10-10 Kostya Khuta

waht是82行'FragmentNews.java'？ – Raghunandan

lvNews.setAdapter（scAdapter）; –

在这部分：else { Log.d（DEBUG_TAG，“wi-fi is off”）; 光标c = db.getNewsFromDb（）;Log.d（DEBUG_TAG，String.valueOf（c.getCount（）））; mySCadapter scAdapter = new mySCadapter（getActivity（），R.layout.item_news，c， from，to）; lvNews。setAdapter（scAdapter）; } –

的问题是，你创建的ListView在onCreateView()中，并将其adapter设置为onCreate() ..

您应该知道onCreate()始终在之前被调用，那时候你的listview没有被创建..那就是你为什么得到NullPointerException。

将您在onCreateView()

来源

2013-10-10 06:36:50 r4jiv007

它的工作原理，感谢所有 –

你的问题的onCreate()代码创建了ListView上onCreateView()方法，并且已经在onCreate()设置适配器。所以onCreate()必须在onCreateView()之前调用，这就是为什么ListViews未初始化，并且您已经找到空指针异常。

来源

2013-10-10 06:40:45

的问题是，你在另一个布局文件创建的ListView，而你是调用同一活动的任何其他布局文件。所以它的不匹配布局调用activity.So地方的ListView在相同的布局，你的活动使用或者如果你想在另一个布局的ListView然后更改ArrayAdapter对象背景如： 改变它

ArrayAdapter适配器=新ArrayAdapter（this， R.layout。，R.id.，）;

与此：

ArrayAdapter适配器=新ArrayAdapter（， R.layout，R.id.，）;

来源

2014-02-03 11:22:47 Davinder

只要把onViewCreated回调您的列表视图代码

试试这个代码：

Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle saveInstanceState) { 
    return inflater.inflate(R.layout.fragment_news, container, false);  
} 

@Override 
public void onViewCreated (View view, Bundle savedInstanceState) { 
    listview = (ListView) view.findViewById(R.id.listview1); 
    try 
    { 
     // put your codes here 
    } catch (Exception e) 
    { 
     e.printStackTrace(); 
    } 
}

来源

2014-04-03 14:53:42

使用onActivityCreated（捆绑savedInstanceState）overrided方法，并尝试把你的代码在。它有助于解决这个崩溃问题。因为在它存在之前创建视图会产生这个异常并导致应用程序崩溃。无论何时从这个视图移动，使用onPause（）和onResume（）都会减少崩溃。

来源

2014-05-29 12:09:19 ManishSB

空指针异常ListView中

回答

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