的NullPointerException在ExpandableListView

我在btn.setOnClickListener得到一个空指针异常的NullPointerException在ExpandableListView

public class ApisimpleActivity extends ExpandableListActivity { 

    ExpandableListAdapter mAdapter; 
Button btn; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     // Set up our adapter 
     setContentView(R.layout.main); 
     btn=(Button)findViewById(R.id.button); 
     btn.setOnClickListener(new OnClickListener(){ 

      @Override 
      public void onClick(View arg0) { 
       // TODO Auto-generated method stub 
      int i=getExpandableListView().getChildCount(); 
      int k=0; 
      //Toast.makeText(ApisimpleActivity.this, "hello"+i, Toast.LENGTH_LONG).show(); 
      for(int j=0;j<i;j++) 
      { 
       View v=(View)getExpandableListView().getChildAt(i); 
       if(v==null) 
       //if(v.findViewById(R.id.chk)==null) 
        k++; 
      } 
      Toast.makeText(ApisimpleActivity.this, k+"",Toast.LENGTH_LONG).show(); 
      }  }); 
     mAdapter = new MyExpandableListAdapter(); 
     setListAdapter(mAdapter); 
     registerForContextMenu(getExpandableListView()); 
    } 

    @Override 
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) { 
     menu.setHeaderTitle("Sample menu"); 
     menu.add(0, 0, 0, "Hello World"); 
    } 

    @Override 
    public boolean onContextItemSelected(MenuItem item) { 
     ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo(); 

     String title = ((TextView) info.targetView).getText().toString(); 

     int type = ExpandableListView.getPackedPositionType(info.packedPosition); 
     if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) { 
      int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
      int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition); 
      Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos, 
        Toast.LENGTH_SHORT).show(); 
      return true; 
     } else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) { 
      int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
      Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show(); 
      return true; 
     } 

     return false; 
    } 

    /** 
    * A simple adapter which maintains an ArrayList of photo resource Ids. 
    * Each photo is displayed as an image. This adapter supports clearing the 
    * list of photos and adding a new photo. 
    * 
    */ 
    public class MyExpandableListAdapter extends BaseExpandableListAdapter { 
     // Sample data set. children[i] contains the children (String[]) for groups[i]. 
     private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" }; 
     private String[][] children = { 
       { "Arnold", "Barry", "Chuck", "David" }, 
       { "Ace", "Bandit", "Cha-Cha", "Deuce" }, 
       { "Fluffy", "Snuggles" }, 
       { "Goldy", "Bubbles" } 
     }; 

     public Object getChild(int groupPosition, int childPosition) { 
      return children[groupPosition][childPosition]; 
     } 

     public long getChildId(int groupPosition, int childPosition) { 
      return childPosition; 
     } 

     public int getChildrenCount(int groupPosition) { 
      return children[groupPosition].length; 
     } 

     public TextView getGenericView() { 
      // Layout parameters for the ExpandableListView 
      AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
        ViewGroup.LayoutParams.FILL_PARENT, 64); 

      TextView textView = new TextView(ApisimpleActivity.this); 
      textView.setLayoutParams(lp); 
      // Center the text vertically 
      textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT); 
      // Set the text starting position 
      textView.setPadding(36, 0, 0, 0); 
      return textView; 
     } 

     public View getChildView(int groupPosition, int childPosition, boolean isLastChild, 
       View convertView, ViewGroup parent) { 
      TextView textView = getGenericView(); 
      textView.setText(getChild(groupPosition, childPosition).toString()); 
      return textView; 
     } 

     public Object getGroup(int groupPosition) { 
      return groups[groupPosition]; 
     } 

     public int getGroupCount() { 
      return groups.length; 
     } 

     public long getGroupId(int groupPosition) { 
      return groupPosition; 
     } 

     public View getGroupView(int groupPosition, boolean isExpanded, View convertView, 
       ViewGroup parent) { 
      View v; 
      v=convertView; 
      if(v==null) 
      {LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
      v = vi.inflate(R.layout.group, null); 
      } 
     return v;} 

     public boolean isChildSelectable(int groupPosition, int childPosition) { 
      return true; 
     } 

     public boolean hasStableIds() { 
      return true; 
     } 

    } 
}

当我调用函数 getExpandableListView（）。getChildAt（i）所有的意见都null.can任何一个请帮助为什么所有的视图都显示为空我需要获取视图并检查每个天气复选框是否被选中或不是。请帮助一下

来源

2011-10-04 Ritesh Mehandiratta