Android applications obtain permission cannot run normally -

wrote contacts , contact phone number , displayed in small program, after permission in android 6 cannot display data, restart program read properly. think should there access out of question, because after restart authority need not ask when can read properly, , need pop-up dialog asking while allowing access permissions still can't show, after restart.

 public class mainactivity extends appcompatactivity {       listview contactsview;       arrayadapter<string> adapter;       list<string> contactslist = new arraylist<string>();       @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);         toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);         setsupportactionbar(toolbar);         contactsview = (listview) findviewbyid(r.id.contacts_view);         adapter = new arrayadapter<string>(this, android.r.layout.                 simple_list_item_1, contactslist);         contactsview.setadapter(adapter);         insertdummycontactwrapper();     }       final private int request_code_ask_permissions = 123;       private void insertdummycontactwrapper() {         int haswritecontactspermission = checkselfpermission(manifest.permission.read_contacts);         if (haswritecontactspermission != packagemanager.permission_granted) {             requestpermissions(new string[] {manifest.permission.read_contacts},                     request_code_ask_permissions);             return;         }         readcontacts();     }       @override     public void onrequestpermissionsresult(int requestcode, string[] permissions, int[] grantresults) {         switch (requestcode) {             case request_code_ask_permissions:                 if (grantresults[0] == packagemanager.permission_granted) {                     // permission granted                     readcontacts();                 } else {                     // permission denied                     toast.maketext(mainactivity.this, "read_contacts denied", toast.length_short)                             .show();                 }                 break;             default:                 super.onrequestpermissionsresult(requestcode, permissions, grantresults);         }     }       public void readcontacts() {         cursor cursor = null;         try {             cursor = getcontentresolver().query(contactscontract.commondatakinds.phone.content_uri,                     null, null, null, null);             while (cursor.movetonext()) {                 string displayname = cursor.getstring(cursor.getcolumnindex(contactscontract.                         commondatakinds.phone.display_name));                 string number = cursor.getstring(cursor.getcolumnindex(contactscontract.                         commondatakinds.phone.number));                 contactslist.add(displayname + "\n" + number);             }         } catch (exception e) {             e.printstacktrace();         } finally {             if (cursor != null) {                 cursor.close();             }         }     }