Android中调用listview 控件的 listview.setAdapter(adapter)程序闪退、崩溃

private ListView listview ;

listview = (ListView)this.findViewById(R.id.listview); 

List<HashMap<String,String>> list=new ArrayList<HashMap<String,String>>();

HashMap<String,String> map1=new HashMap<String,String>();

HashMap<String,String> map2 = new HashMap<String,String>();

map1.put("user_name","user1");         

map1.put("user_ip","192.168.9.1");

map2.put("user_name","user2");

map2.put("user_ip", "192.165");

list.add(map1);

list.add(map2);

SimpleAdapter adapter =new SimpleAdapter(MainActivity.this, list, R.layout.item, new String[]{"user_name","user_ip"}, new int[]{R.id.qishu,R.id.yuegong});

listview.setAdapter(adapter);