java - Null pointer exception when trying to pass a customAdapter? -

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• what nullpointerexception, , how fix it? 12 answers

public class jsonviewpager  { private volleysingleton mvolleysingleton; private viewpageradapter mviewpageradapter; private requestqueue mrequestqueue; private string murl; private arraylist<questiondata> mquestiondataarraylist = new      arraylist<questiondata>();  public jsonviewpager(viewpageradapter viewpageradapter,string url){     mviewpageradapter=viewpageradapter;     murl=url; } public void jsonrequestmethod() {     mvolleysingleton = volleysingleton.getinstance();     mrequestqueue = mvolleysingleton.getrequestqueue();     jsonarrayrequest request = new jsonarrayrequest(request.method.get, murl, (string) null, new response.listener<jsonarray>() {         @override         public void onresponse(jsonarray response) {             parse parsejsonresponse=new parse();             mquestiondataarraylist = parsejsonresponse(response);             mviewpageradapter.setbloglist(mquestiondataarraylist);         }      }, new response.errorlistener() {         @override         public void onerrorresponse(volleyerror error) {         }     });     mrequestqueue.add(request); } } 

i have class in passing viewpageradapter from, set viewpageradapter in oncreateview in other class, reason getting null pointer exception when @ mviewpageradapter.setbloglist(mquestiondataarraylist); line. know causing this?

home class

public class home extends fragment { private static final int refresh_delay=500; private static final string arg_param1 = "param1"; private static final string arg_param2 = "param2"; //url reflects ordered list on server filter terms {"include": {"relation": "questions", "scope": {"order" : "points desc"}}}) private static final string url_home="hiddenurl";  private string mparam1; private string mparam2; private imageview mimageview; private volleysingleton mvolleysingleton; private requestqueue mrequestqueue; private recyclerview mrecyclerview;  private arraylist<questiondata> mlistblogs = new arraylist<>(); private arraylist<questiondata> mquestiondataarraylist = new     arraylist<questiondata>(); private pulltorefreshview mpulltorefreshview; private viewpageradapter mviewpageradapter;  public static home newinstance(string param1, string param2) {     home fragment = new home();     bundle args = new bundle();     args.putstring(arg_param1, param1);     args.putstring(arg_param2, param2);     fragment.setarguments(args);     return fragment;  }  public home() {     // required empty public constructor }  @override public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     if (getarguments() != null) {         mparam1 = getarguments().getstring(arg_param1);         mparam2 = getarguments().getstring(arg_param2);     }     //if wish handle event source in activity main thread, you’ll need add following instructions @ beginning of oncreate() android callback:     system.out.println("userid" + login.getuserid());     system.out.println("username" + login.getusername());     jsonviewpager s=new jsonviewpager(mviewpageradapter,url_home);     s.jsonrequestmethod(); }  @override public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {     // inflate layout fragment     view view = inflater.inflate(r.layout.fragment_home, container, false);     mrecyclerview = (recyclerview) view.findviewbyid(r.id.fragment_dashboard_recycler);     mrecyclerview.setlayoutmanager(new linearlayoutmanager(getactivity()));     mviewpageradapter = new viewpageradapter(getactivity());      mrecyclerview.setadapter((mviewpageradapter));     mpulltorefreshview = (pulltorefreshview) view.findviewbyid(r.id.pull_to_refresh);      mpulltorefreshview.setonrefreshlistener(new pulltorefreshview.onrefreshlistener() {         @override         public void onrefresh() {             mpulltorefreshview.postdelayed(new runnable() {                 @override                 public void run() {                     mpulltorefreshview.setrefreshing(false);                     jsonrequestmethod();                 }             }, refresh_delay);         }     });     return view; } } 

you calling

jsonviewpager s=new jsonviewpager(mviewpageradapter,url_home); 

in oncreate method, , then

mviewpageradapter = new viewpageradapter(getactivity()); 

in oncreateview method.

the problem in activity lifecycle, oncreateveiw come after oncreate, meaning jsonviewepager object created passing in null value of mviewpageradapter.

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