NullPointerException: वर्चुअल विधि 'int java.util.ArrayList.size()' को एक शून्य ऑब्जेक्ट संदर्भ

Question

पर आक्रमण करने का प्रयास करें, मैं Fragments और कस्टम ListView एडेप्टर के लिए नौसिखिया हूं। क्या कोई मुझे हाथ दे सकता है?

मुझे मिल गया है मेरी Fragment जहां मैं अपने ListView

public class RecordingListFragment extends Fragment implements OnItemClickListener { 

    ListView mListView; 
    TextView emptyView; 
    Button options, delete,edit; 
    ArrayList<String> recordings = null; 
    RecordingsListAdapter mAdapter; 

    public RecordingListFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.recording_list_fragment, container,false); 

     options = (Button) rootView.findViewById(R.id.options); 
     edit = (Button) rootView.findViewById(R.id.edit); 
     delete = (Button) rootView.findViewById(R.id.delete); 
     mListView = (ListView) rootView.findViewById(R.id.list); 
     emptyView = (TextView) rootView.findViewById(R.id.empty); 


     mAdapter = new RecordingsListAdapter(this, recordings); 
     mListView.setAdapter(mAdapter); 
     mListView.setEmptyView(emptyView); 
     mListView.setOnItemClickListener(this); 

     return rootView; 
    } 
} 

और मेरे एक्सएमएल अपने कस्टम सूची आइटम है यह

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    xmlns:android1="http://schemas.android.com/apk/res/android" 
    android:id="@+id/recording_list_fragment" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:background="#ffffff" 
    android:orientation="vertical"> 

    <RelativeLayout 
     android:layout_height="50dp" 
     android:layout_width="match_parent" 
     android:orientation="horizontal" 
     android:background="@drawable/title" > 

     <TextView 
      android1:id="@+id/title" 
      android1:layout_width="wrap_content" 
      android1:layout_height="50dp" 
      android1:layout_alignParentTop="true" 
      android1:layout_centerHorizontal="true" 
      android1:layout_marginStart="80dp" 
      android1:gravity="center" 
      android1:text="@string/app_name" 
      android1:textAlignment="center" 
      android1:textColor="#000000" 
      android1:textStyle="bold" /> 

    </RelativeLayout> 

    <FrameLayout 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent"> 

     <ListView 
      android:id="@+id/list" 
      android:animateLayoutChanges="true" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent"/> 
     <!-- android:divider="@null"--> 

     <TextView 
      android:id="@+id/empty" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:gravity="center" 
      android:text="@string/empty_list_text" 
      android:paddingLeft="30dp" 
      android:paddingRight="30dp" 
      android:paddingTop="180dp" /> 

    </FrameLayout> 
</LinearLayout> 

और मुझे मिल गया है के लिए

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

    <CheckedTextView 
     android:id="@+id/textView" 
     android:layout_width="fill_parent" 
     android:layout_height="?android:attr/listPreferredItemHeight" 
     android:textAppearance="?android:attr/textAppearanceLarge" 
     android:gravity="center_vertical" 
     android:checkMark="?android:attr/listChoiceIndicatorSingle" 
     android:paddingLeft="6dip" 
     android:paddingRight="6dip" 
     android:textColor="#000000" 
     /> 

</LinearLayout> 

और अंत में, मेरे Adapter

public class RecordingsListAdapter extends BaseAdapter { 
    Context ctx; 
    LayoutInflater lInflater; 
    ArrayList<String> recordings; 

    RecordingsListAdapter(Context context, ArrayList<String> products) { 
     ctx = context; 
     recordings = products; 
     lInflater = (LayoutInflater) ctx 
     .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
    } 

    public RecordingsListAdapter(RecordingListFragment recordingListFragment, 
    ArrayList<String> recordings) { 
     // TODO Auto-generated constructor stub 
    } 


    @Override 
    public int getCount() { 
     return recordings.size(); 
    } 


    @Override 
    public Object getItem(int position) { 
     return recordings.get(position); 
    } 


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


    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 

     View view = convertView; 
     if (view == null) { 
      view = lInflater.inflate(R.layout.custom_list_item, parent, false); 
     } 

     return view; 
    } 
} 

और जब मैं इस चलाने के लिए, मैं इस नल पॉइंटर

11-26 11:00:45.352: E/AndroidRuntime(10191): java.lang.RuntimeException: Unable to start activity ComponentInfo{d/recordings.RecordingsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread.access$800(ActivityThread.java:144) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.os.Handler.dispatchMessage(Handler.java:102) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.os.Looper.loop(Looper.java:135) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread.main(ActivityThread.java:5221) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at java.lang.reflect.Method.invoke(Native Method) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at java.lang.reflect.Method.invoke(Method.java:372) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
11-26 11:00:45.352: E/AndroidRuntime(10191): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference 
11-26 11:00:45.352: E/AndroidRuntime(10191): at recordings.RecordingsListAdapter.getCount(RecordingsListAdapter.java:36) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.widget.ListView.setAdapter(ListView.java:487) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at recordings.RecordingListFragment.onCreateView(RecordingListFragment.java:47) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.Fragment.performCreateView(Fragment.java:2053) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.BackStackRecord.run(BackStackRecord.java:833) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.Activity.performStart(Activity.java:5948) 
11-26 11:00:45.352: E/AndroidRuntime(10191): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261) 
11-26 11:00:45.352: E/AndroidRuntime(10191): ... 10 more 

अग्रिम धन्यवाद मिल !!!

Answer 1

आपने रिकॉर्डिंग प्रारंभ करना चाहिए बनाते हैं। आप एडाप्टर शून्य

ArrayList<String> recordings = null; //You are passing this null 

Answer 2

बदलें

mAdapter = new RecordingsListAdapter(this, recordings); 

mAdapter = new RecordingsListAdapter(getActivity(), recordings); 

और यह भी करने के लिए सुनिश्चित करें कि recordings!=nullmAdapter = new RecordingsListAdapter(this, recordings); पर

Answer 3

यह समस्या ArrayList चर के कारण तत्काल नहीं हो रही है। निम्नलिखित "रिकॉर्डिंग" चर घोषित करने की आवश्यकता है, जो समस्या को हल करना चाहिए;

ArrayList<String> recordings = new ArrayList<String>(); 

यह डिफ़ॉल्ट निर्माता कॉल करता है और रिकॉर्डिंग चर करने के लिए रिक्त स्ट्रिंग प्रदान करती है इतना है कि यह अब और अशक्त नहीं है।