誤差片段

Question

目前，我正在學習用碎片的工作，到目前爲止，我已經相當成功，但已經提出了以下錯誤：

10-14 15:24:55.309 21831-21831/? E/AndroidRuntime: FATAL EXCEPTION: main 
10-14 15:24:55.309 21831-21831/? E/AndroidRuntime: Process: com.example.wq.myapp, PID: 21831 
10-14 15:24:55.309 21831-21831/? E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
10-14 15:24:55.309 21831-21831/? E/AndroidRuntime:  at com.example.wq.myapp.PhoneMessages.onActivityCreated(PhoneMessages.java:44) 

如果任何人都可以解釋我做錯了什麼這將不勝感激:)

這裏是我的代碼片段：

package com.example.wq.myapp; 


import android.content.ContentResolver; 
import android.content.Intent; 
import android.database.Cursor; 
import android.net.Uri; 
import android.os.Bundle; 
import android.app.Fragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.ListView; 
import android.widget.SimpleCursorAdapter; 
import android.widget.TextView; 

public class PhoneMessages extends Fragment { 

    ListView lvMsgList; 

    // Cursor Adapter 
    SimpleCursorAdapter adapter1; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     // Inflate the layout for this fragment 
     return inflater.inflate(R.layout.fragment_phone_messages, container, false); 
    } 

    @Override 
    public void onActivityCreated(Bundle savedInstanceState) { 

     // Create Inbox box URI 
     Uri inboxURI = Uri.parse("content://mms-sms/conversations"); 
     // Fetch Inbox SMS Message from Built-in Content Provider 
     Cursor a = getActivity().getContentResolver().query(inboxURI, new String[]{"*"}, null, null, "normalized_date desc"); 
     // Attach Cursor with adapter and display in listView 
     adapter1 = new SimpleCursorAdapter(getActivity().getApplicationContext(), R.layout.row, a, 
       new String[]{"body", "date", "address", "thread_id"}, 
       new int[]{R.id.lblMsg, R.id.lblDate, R.id.lblNumber, R.id.lblID}, 0); 
     lvMsgList.setAdapter(adapter1); 
     //set OnItemClickListener for listView, start ConvListActivity 
     lvMsgList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
       TextView TVConvID = (TextView) view.findViewById(R.id.lblID); 
       String ConvID = TVConvID.getText().toString(); 
       Intent i = new Intent(getActivity(), ConvListActivity.class); 
       i.putExtra("CID", ConvID); 
       startActivity(i); 
      } 
     }); 
     getActivity().setTitle("Phone Messages"); 
    } 
} 

Answer 1

你永遠不誇大你的ListView，所以你得到一個空指針。在onCreateView中做它也更好。

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 
    // Inflate the layout for this fragment 
    View rootView = inflater.inflate(R.layout.fragment_phone_messages, container, false); 

    lvMsgList = (ListView) rootView.findViewById(R.id./*listview*/); 

    // Create Inbox box URI 
    Uri inboxURI = Uri.parse("content://mms-sms/conversations"); 
    // Fetch Inbox SMS Message from Built-in Content Provider 
    Cursor a = getActivity().getContentResolver().query(inboxURI, new String[]{"*"}, null, null, "normalized_date desc"); 
    // Attach Cursor with adapter and display in listView 
    adapter1 = new SimpleCursorAdapter(getActivity().getApplicationContext(), R.layout.row, a, 
      new String[]{"body", "date", "address", "thread_id"}, 
      new int[]{R.id.lblMsg, R.id.lblDate, R.id.lblNumber, R.id.lblID}, 0); 
    lvMsgList.setAdapter(adapter1); 
    //set OnItemClickListener for listView, start ConvListActivity 
    lvMsgList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
      TextView TVConvID = (TextView) view.findViewById(R.id.lblID); 
      String ConvID = TVConvID.getText().toString(); 
      Intent i = new Intent(getActivity(), ConvListActivity.class); 
      i.putExtra("CID", ConvID); 
      startActivity(i); 
     } 
    }); 
    getActivity().setTitle("Phone Messages"); 

    return rootView; 
}