NullPointerException Android的片段

我知道这个问题已经被问了很多，我很抱歉问，但我完全失去了，并试图学习这一点。NullPointerException Android的片段

所以我理解空指针的一般概念，但我在SImpleCursorAdpater上遇到了问题。我试图用简单的适配器来填充我的片段列表视图，但我遇到了这个问题

在片段

public void onActivityCreated (Bundle savedInstanceState) { 
    super.onActivityCreated(savedInstanceState); 

    //opeing the DBApater 
    db = new DBAdapter(getActivity()); 
    try { 
     db.open(); 
    } catch (SQLException e) { 
     e.printStackTrace(); 
    } 
    //opening the Recipes_Adapter 
    recipes = new Recipes_Adapter(getActivity()); 
    try { 
     recipes.open(); 
    } catch (SQLException e) { 
     e.printStackTrace(); 
    } 


    Cursor cursor = recipes.getAllRecipes(); 

    String[] columns = new String[] {Recipes_Adapter.NAME}; 
    int[] to = new int[] {R.id.recipe_name}; 

    SimpleCursorAdapter myCursorAdapter = new SimpleCursorAdapter(getActivity(),R.layout.row,cursor, columns,to, 0); 

    ListView recipeList = (ListView)rootview.findViewById(R.id.recipe_list); 
    recipeList.setAdapter(myCursorAdapter); //error is on this line 

}

R.layout.row

创建适配器

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" > 

    <TextView 
     android:id="@+id/recipe_name" 
     android:paddingLeft="5dp" 
     android:textSize="17dp" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="TextView" /> 

</LinearLayout>

配方Layout.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:background="#D1FFFF" 
    android:orientation="vertical"> 

    <ListView 
     android:id="@+id/recipe_list" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
     android:dividerHeight="0.1dp" 
     android:divider="#0000CC" 
     > 
    </ListView> 

</LinearLayout>

logcat的

10-13 20:13:48.914 10625-10625/? E/AndroidRuntime: FATAL EXCEPTION: main 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime: Process: app.rory.menu, PID: 10625 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{app.rory.menu/app.rory.pocket_chef.MyActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.access$800(ActivityThread.java:151) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:102) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5254) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at app.rory.pocket_chef.Fragments.recipes_Fragment.onActivityCreated(recipes_Fragment.java:63) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.Fragment.performActivityCreated(Fragment.java:2061) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:912) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.BackStackRecord.run(BackStackRecord.java:834) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.Activity.performStart(Activity.java:6005) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2288) 
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.access$800(ActivityThread.java:151)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:102)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:135)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5254)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Method.java:372)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)  
10-13 20:13:48.914 10625-10625/? E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

来源

2015-10-13 Rory

代码看起来不错，把你的logcat和删除最后的关键字从ListView –

在哪里设置Fragment的食谱布局布局？ –

更新的问题，以显示日志 – Rory

移动内部onActivityCreated编写的所有代码（）方法来onViewCreated（）方法，它将工作。基本上onActivityCreated不能保证你的xml已经被夸大了，所有的视图都存在于视图层次结构中，但是onViewCreated（）会有。

来源

2015-10-13 19:30:05 dex

NullPointerException Android的片段

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