Exception for listview adapter when listview is missing(Fragment) -

1) activity has many fragment, fragments can switch another(whole rootview change) navigation drawer.

2) have listview in fragment update using simple adapter.

3) if switch fragment while listview still loading. -an error occur.

may know how make exception this??

i extend simple adapter listview

listadapter adapter = new extendedsimpleadapter(                                 getactivity(), news_list,                                 r.layout.news_item, new string[]{"news", "datetime", "desc","day"},                                 new int[]{r.id.news, r.id.new_time, r.id.desc,r.id.day});                         setlistadapter(adapter); 

this custom adapter :

public class extendedsimpleadapter extends simpleadapter{       context context2;      public extendedsimpleadapter(context context, list<? extends map<string, string>> data, int     resource, string[] from, int[] to){         super(context, data, resource, from, to);         context2=context;     }      public view getview(int position, view convertview, viewgroup parent){         // here let simpleadapter built view normally.         view v = super.getview(position, convertview, parent);          // reference picasso         imageview img = (imageview) v.gettag();         textview txt = (textview) v.findviewbyid(r.id.state);         if(img == null){             img = (imageview) v.findviewbyid(r.id.new_pic);              v.settag(img);         }         // url data passed `map`         string url =  ((map<string, string>)getitem(position)).get("pic");         string type =  ((map<string, string>)getitem(position)).get("type");         string state =  ((map<string, string>)getitem(position)).get("state");         if (type.equals("reward"))         {             txt.setvisibility(view.visible);         }         else         {             txt.setvisibility(view.gone);         }         if(url.equals("")){             picasso.with(context2).load(r.drawable.default).into(img);          }         else{             picasso.with(context2)                     .load(url)                     .placeholder(r.drawable.default)                     .resize(100, 100)                     .centercrop()                     .into(img);         }          // return view          return v;     } } 

the error message nullpointerexception

e/androidruntime﹕ fatal exception: main     process: com.werebits.chopinkmerchant, pid: 14486     java.lang.nullpointerexception             @ android.widget.simpleadapter.<init>(simpleadapter.java:85)             @ com.werebits.chopinkmerchant.extendedsimpleadapter.<init>(extendedsimpleadapter.java:19)             @ com.werebits.chopinkmerchant.home$placeholderfragment$4.onsuccess(home.java:488)             @ com.loopj.android.http.jsonhttpresponsehandler$1$1.run(jsonhttpresponsehandler.java:128)             @ android.os.handler.handlecallback(handler.java:733)             @ android.os.handler.dispatchmessage(handler.java:95)             @ android.os.looper.loop(looper.java:136)             @ android.app.activitythread.main(activitythread.java:5230)             @ java.lang.reflect.method.invokenative(native method)             @ java.lang.reflect.method.invoke(method.java:515)             @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:780)             @ com.android.internal.os.zygoteinit.main(zygoteinit.java:596)             @ dalvik.system.nativestart.main(native method) 

is means when switch fragment when listview still loading, adapter can't find listview??

how add exception this???