解决：SwipeListViews'findViewById'的空指针'

Question

我的应用程序使用主要活动和片段。我已经在包含自定义列表视图的片段下设置了swipelistview。在执行时，应用程序崩溃与日志猫报告以下错误：

02-17 15:20:17.897: E/AndroidRuntime(5759): Caused by: java.lang.NullPointerException 02-17 15:20:17.897: E/AndroidRuntime(5759): at com.fragments.Frag1.onCreateView(Frag1.java:71)

而下面的语句在位于行＃Frag1.java 71：

swipelistview=(SwipeListView)getView().findViewById(R.id.example_swipe_lv_list);

我已经声明了example_swipe_lv_list项目在调用getView（）时膨胀的XML内部。

我正在测试的例子http://www.tutecentral.com/android-swipe-listview/但是，带有碎片。

什么可能导致此问题？

编辑：

这里是全片段代码：

import java.util.ArrayList; 
import java.util.List; 

import android.app.Fragment; 
import android.content.Context; 
import android.content.res.Resources; 
import android.graphics.Typeface; 
import android.media.MediaPlayer; 
import android.os.Bundle; 
import android.util.DisplayMetrics; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.BaseAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.TextView; 

import com.example.ItemAdapter; 
import com.example.ItemRow; 
import com.example.R; 
import com.fortysevendeg.swipelistview.BaseSwipeListViewListener; 
import com.fortysevendeg.swipelistview.SwipeListView; 

public class MyList extends Fragment { 


    @Override 
    public void onPause() { 
     // TODO Auto-generated method stub 
     super.onPause(); 

     index = list.getFirstVisiblePosition(); 
    } 

    @Override 
    public void onResume() { 
     // TODO Auto-generated method stub 
     super.onResume(); 

     list.setSelectionFromTop(index, 0); 
    } 

    ListView list; 
    int index = 0; 
    MediaPlayer mp; 

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

     mp=MediaPlayer.create(getActivity(), R.raw.1); 


     return inflater.inflate(R.layout.listview, container, false); 
    } 


    @Override 
    public void onStart() { 

     super.onStart(); 
     list=(ListView)getView().findViewById(R.id.listView1); 
     list.setAdapter(new MyAdapter(getActivity())); 

     list.setOnItemClickListener(new OnItemClickListener(){ 

      @Override 
      public void onItemClick(AdapterView<?> arg0, View arg1, int position, 
        long arg3) 

      { 

       switch(position) 
        { 
        case 0: 
         mp.release(); 
         mp=MediaPlayer.create(getActivity(), R.raw.1); 
         mp.start(); 

        break; 

        case 1: 
         mp.release(); 
         mp=MediaPlayer.create(getActivity(), R.raw.2); 
         mp.start(); 
         break; 

        case 2: 
         mp.release(); 
         mp=MediaPlayer.create(getActivity(), R.raw.3); 
         mp.start();  
         break; 

        case 3: 
         mp.release(); 
         mp=MediaPlayer.create(getActivity(), R.raw.4); 
         mp.start(); 
         break; 

        case 4: 
         mp.release(); 
         mp=MediaPlayer.create(getActivity(), R.raw.5); 
         mp.start(); 
         break; 

        } 
      } 
      }); 
    } 
} 

    class MyAdapter extends BaseAdapter 
    { 
     ArrayList<SingleRow> list; 
     Context context; 

     public MyAdapter(Context c) { 

      context=c; 
      list=new ArrayList<SingleRow>(); 
      //Initialize them... 
      Resources res=c.getResources(); 
      String[] dialogues = res.getStringArray(R.array.dialogues); 
      int[] images={ 

        R.drawable.ics, 
        R.drawable.ics, 
        R.drawable.ics, 
        R.drawable.ics, 
        R.drawable.ics, 
        R.drawable.ics, 
        R.drawable.ics, 

        }; 

      for(int i=0;i<38;i++) 
      { 
       list.add(new SingleRow(dialogues[i],images[i])); 
      } 

     } 

public int convertDpToPixel(float dp) { 
     DisplayMetrics metrics =context.getResources().getDisplayMetrics(); 
     float px = dp * (metrics.densityDpi/160f); 
     return (int) px; 
    } 
     @Override 
     public int getCount() { 
      // TODO Auto-generated method stub 
      return list.size(); 
     } 

     @Override 
     public Object getItem(int position) { 
      // TODO Auto-generated method stub 

      return list.get(position); 
     } 

     @Override 
     public long getItemId(int position) { 

      return position; 
     } 

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

     View row=convertView; 
     MyViewHolder holder=null; 
     itemData=new ArrayList<ItemRow>(); 
     adapter=new ItemAdapter(context,R.layout.custom_row,itemData); 
     SwipeListView swipelistview; 

      swipelistview.setSwipeListViewListener(new BaseSwipeListViewListener() { 
       @Override 
       public void onOpened(int position, boolean toRight) { 
       } 

       @Override 
       public void onClosed(int position, boolean fromRight) { 
       } 

       @Override 
       public void onListChanged() { 
       } 

       @Override 
       public void onMove(int position, float x) { 
       } 

       @Override 
       public void onStartOpen(int position, int action, boolean right) { 
        Log.d("swipe", String.format("onStartOpen %d - action %d", position, action)); 
       } 

       @Override 
       public void onStartClose(int position, boolean right) { 
        Log.d("swipe", String.format("onStartClose %d", position)); 
       } 

       @Override 
       public void onClickFrontView(int position) { 
        Log.d("swipe", String.format("onClickFrontView %d", position)); 

        swipelistview.openAnimate(position); //when you touch front view it will open 

       } 

       public void onClickBackView(int position) { 
        Log.d("swipe", String.format("onClickBackView %d", position)); 

        swipelistview.closeAnimate(position);//when you touch back view it will close 
       } 

       public void onDismiss(int[] reverseSortedPositions) { 

       } 

      }); 

      //These are the swipe listview settings. you can change these 
      //setting as your requirement 
      swipelistview.setSwipeMode(SwipeListView.SWIPE_MODE_LEFT); // there are five swiping modes 
      swipelistview.setSwipeActionLeft(SwipeListView.SWIPE_ACTION_REVEAL); //there are four swipe actions 
      swipelistview.setSwipeActionRight(SwipeListView.SWIPE_ACTION_REVEAL); 
      swipelistview.setOffsetLeft(convertDpToPixel(260f)); // left side offset 
      swipelistview.setOffsetRight(convertDpToPixel(0f)); // right side offset 
      swipelistview.setAnimationTime(50); // Animation time 
      swipelistview.setSwipeOpenOnLongPress(true); // enable or disable SwipeOpenOnLongPress 

      swipelistview.setAdapter(adapter); 

      for(int i=0;i<10;i++) 
      { 
       itemData.add(new ItemRow("item"+i,getResources().getDrawable(R.drawable.ic_launcher))); 

      } 

      adapter.notifyDataSetChanged(); 


     if(row==null) 
     { 
      LayoutInflater inflater=(LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      row=inflater.inflate(R.layout.list_rows, parent, false); 
      swipelistview = (SwipeListView)row.findViewById(R.id.example_swipe_lv_list); 
      row.setBackgroundResource(R.drawable.coloria); 
      holder=new MyViewHolder(row); 
      SingleRow temp=list.get(position); 

      holder.imageView.setImageResource(temp.image); 

      row.setTag(holder); 
     } 

     else 
     { 
      holder=(MyViewHolder)row.getTag(); 
     } 
     SingleRow temp=list.get(position); 

     holder.textView.setText(temp.description); 

     Typeface font = Typeface.createFromAsset(holder.textView.getContext().getAssets(), "fonts/OpenSans.ttf"); 

     holder.textView.setTypeface(font); 

     return row; 
    } 

class MyViewHolder 
{ 
    ImageView imageView; 
    TextView textView; 

    MyViewHolder(View v) 
    { 
     textView=(TextView)v.findViewById(R.id.textView1); 
     imageView=(ImageView)v.findViewById(R.id.imageView1); 
    } 
} 

class SingleRow 
{ 
    String description; 
    int image; 
    SingleRow(String description, int image) 
    { 
     this.description=description; 
     this.image=image; 
    } 
} 

    } 

Answer 1

不能使用getView()onCreateView()叫前或完成（所以你不能用它里面onCreateView()以及）。

可以使用充气视图调用findViewById()：

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.some_fragment, container, false); 
    swipelistview=(SwipeListView)view.findViewById(R.id.example_swipe_lv_list); 
    return view; 
}