java - Null Pointer Exception in Adapter for recyclerview -
i've been trying implement recyclerview activity keep getting nullpointerexception. first time making recyclerview if i'm doing wrong tell me. i'll show code tell where error at
my main xml layout (called activity_main.xml)
<android.support.v4.widget.drawerlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:card_view="http://schemas.android.com/apk/res-auto" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/drawer" android:fitssystemwindows="true"> <linearlayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <include android:id="@+id/tool_bar" layout="@layout/tool_bar"> </include> <android.support.v7.widget.recyclerview android:id="@+id/main_recycler_view" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingright="8dp" android:paddingleft="8dp" android:paddingtop="8dp"/> </linearlayout> <android.support.design.widget.navigationview android:id="@+id/navigation_view" android:layout_width="wrap_content" android:layout_height="match_parent" android:layout_gravity="start" app:headerlayout="@layout/drawer_header" app:menu="@menu/drawer"/> </android.support.v4.widget.drawerlayout> my row xml recyclerview (called main_recycler_view_row.xml)
<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v7.widget.cardview android:id="@+id/main_card" android:layout_width="match_parent" android:layout_height="wrap_content"> <linearlayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical"> <textview android:id="@+id/period_title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textsize="24sp" android:textcolor="@android:color/black" android:paddingtop="24dp" android:paddingleft="16dp" android:paddingbottom="4dp"/> <textview android:id="@+id/period_subtitle" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textsize="14sp" android:paddingleft="16dp" android:paddingbottom="16dp"/> </linearlayout> </android.support.v7.widget.cardview> </linearlayout> my main activity
package maxbleggi.afstudentplanner; import android.content.intent; import android.content.res.configuration; import android.support.design.widget.navigationview; import android.support.v4.view.gravitycompat; import android.support.v4.widget.drawerlayout; import android.support.v7.app.actionbardrawertoggle; import android.support.v7.app.appcompatactivity; import android.support.v7.app.actionbar; import android.support.v7.widget.linearlayoutmanager; import android.support.v7.widget.recyclerview; import android.support.v7.widget.toolbar; import android.os.bundle; import android.view.menu; import android.view.menuitem; import android.view.view; import android.widget.adapterview; import android.widget.arrayadapter; import android.widget.button; import android.widget.listview; import android.widget.toast; import com.parse.getcallback; import com.parse.parse; import com.parse.parseexception; import com.parse.parseobject; import com.parse.parsequery; import com.parse.parseuser; import java.util.arraylist; import java.util.list; public class mainactivity extends appcompatactivity { // "macros" user's class periods private final int period1 = 0; private final int period2 = 1; private final int period3 = 2; private final int period4 = 3; private final int period5 = 4; private final int period6 = 5; private final int period7 = 6; // toolbar private toolbar toolbar; // nav drawer private drawerlayout navdrawer; // user's data private string[] userclasses = new string[10]; // list fill classroom class private list<classroomclass> classrooms; /* * on creation of activity */ @override protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); // initialise , set toolbar actionbar toolbar = (toolbar) findviewbyid(r.id.tool_bar); setsupportactionbar(toolbar); // initialize drawer layout navdrawer = (drawerlayout) findviewbyid(r.id.drawer); navigationview navview = (navigationview) findviewbyid(r.id.navigation_view); // initialize recycler view elements recyclerview mainrecyclerview = (recyclerview)findviewbyid(r.id.main_recycler_view); // initialize layout manager recycler view recyclerview.layoutmanager mainlayoutmanager = new linearlayoutmanager(this); // adapter recycler view recyclerview.adapter mainadapter= new mainrecycleradapter(classrooms);; // initialize nav bars initnavbars(); // initialize nav drawer initnavdrawer(); // initialize data classes initclassdata(); // add layout manager recycler view mainrecyclerview.setlayoutmanager(mainlayoutmanager); // add adapter recycler view mainrecyclerview.setadapter(mainadapter); } /* * initializes class data each class */ public void initclassdata() { // check if user not cached parseuser currentuser = parseuser.getcurrentuser(); if (currentuser == null) { // prompt user register screen intent intent = new intent(mainactivity.this, registeractivity.class); intent.addflags(intent.flag_activity_new_task); intent.addflags(intent.flag_activity_clear_task); startactivity(intent); } // query database user's classes final parsequery<parseobject> query = parsequery.getquery("studentclasses"); query.whereequalto("student_id", parseuser.getcurrentuser()); query.getfirstinbackground(new getcallback<parseobject>() { @override public void done(parseobject parseobject, parseexception e) { if (parseobject == null) { // retrieved object userclasses[period1]= parseobject.getstring("first_period"); userclasses[period2]= parseobject.getstring("second_period"); userclasses[period3]= parseobject.getstring("third_period"); userclasses[period4]= parseobject.getstring("fourth_period"); userclasses[period5]= parseobject.getstring("fifth_period"); userclasses[period6]= parseobject.getstring("sixth_period"); userclasses[period7]= parseobject.getstring("seventh_period"); } else { // failed lookup. here } } }); // fill fields class periods classrooms = new arraylist<>(); // titles of classes add list string[] classtitles = {"first period", "second period", "third period", "fourth period", "fifth period", "sixth period", "seventh period"}; // iterate on every period add list (int = 0; <= period7; i++) { // if period registered "nothing" don't add list //if (!userclasses[i].equals("nothing")) //{ classrooms.add(new classroomclass(userclasses[i], classtitles[i], + 1)); //} } } public void initnavdrawer() { navdrawer = (drawerlayout) findviewbyid(r.id.drawer); final navigationview navview = (navigationview) findviewbyid(r.id.navigation_view); navview.setnavigationitemselectedlistener(new navigationview.onnavigationitemselectedlistener() { @override public boolean onnavigationitemselected(menuitem menuitem) { menuitem.setchecked(true); navdrawer.closedrawers(); return true; } }); } private void initnavbars() { if (toolbar != null) { getsupportactionbar().setdisplayhomeasupenabled(true); toolbar.setnavigationicon(r.drawable.ic_menu_white); toolbar.setnavigationonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { navdrawer.opendrawer(gravitycompat.start); } }); } } } my class data fields
package maxbleggi.afstudentplanner; /* * define characteristics classroom cards have in common */ public class classroomclass { string classname; string classperiod; int classnumber; public classroomclass(string classname, string classperiod, int classnumber) { this.classname = classname; this.classperiod = classperiod; this.classnumber = classnumber; } public string getclassname() { return classname; } public string getclassperiod() { return classperiod; } public int getclassnumber() { return classnumber; } } finally adapter
package maxbleggi.afstudentplanner; import android.support.v7.widget.cardview; import android.support.v7.widget.recyclerview; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.textview; import java.util.list; public class mainrecycleradapter extends recyclerview.adapter<mainrecycleradapter.viewholder> { private list<classroomclass> classrooms; public static class viewholder extends recyclerview.viewholder { // hold data items public view view; viewholder(view itemview) { super(itemview); view = itemview; } } public mainrecycleradapter(list<classroomclass> classrooms) { this.classrooms = classrooms; } @override public viewholder oncreateviewholder(viewgroup viewgroup, int i) { // create new view view v = layoutinflater.from(viewgroup.getcontext()).inflate(r.layout.main_recycler_view_row, viewgroup, false); // set view's parameters viewholder pvh = new viewholder(v); return pvh; } @override public void onbindviewholder(viewholder viewholder, int position) { // elements view textview title = (textview) viewholder.view.findviewbyid(r.id.period_title); textview subtitle = (textview) viewholder.view.findviewbyid(r.id.period_subtitle); // retrieve data data field , put in view title.settext(classrooms.get(position).getclassname()); subtitle.settext(classrooms.get(position).classperiod); } @override public int getitemcount() { return classrooms.size(); } @override public void onattachedtorecyclerview(recyclerview recyclerview) { super.onattachedtorecyclerview(recyclerview); } } i java.lang.nullpointerexception in mainrecycleradapter @ item count here
@override public int getitemcount() { return classrooms.size(); } any or comments appreciated , sorry code. wanted make sure thorough.
you call
initclassdata(); after call of constructor:
recyclerview.adapter mainadapter= new mainrecycleradapter(classrooms);; this reason of nullpoimter. object classrooms still empty when invoke size() on nullpoint.
just replace order of lines.
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