The application crashes with an error stating that the Recyclerview is being called on a null object. However I can't seem to pinpoint what is causing this issue. Any help would be very much appreciated. If anymore code is needed, do let me know and I'll edit it in.
Logcat error:
2019-10-30 23:59:15.235 10878-10878/com.example.zaphk.studenthelperapplication3 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.zaphk.studenthelperapplication3, PID: 10878
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.zaphk.studenthelperapplication3/com.example.zaphk.studenthelperapplication3.view.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2861)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2943)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1630)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6626)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:811)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.example.zaphk.studenthelperapplication3.view.MainActivity.onCreate(MainActivity.java:65)
at android.app.Activity.performCreate(Activity.java:7032)
at android.app.Activity.performCreate(Activity.java:7023)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1236)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2814)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2943)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1630)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6626)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:811)
MainActivity.java
package com.example.zaphk.studenthelperapplication3.view;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
import com.example.zaphk.studenthelperapplication3.database.DatabaseHelper;
import com.example.zaphk.studenthelperapplication3.database.model.Note;
import com.example.zaphk.studenthelperapplication3.utils.MyDividerItemDecoration;
import com.example.zaphk.studenthelperapplication3.utils.RecyclerTouchListener;
import com.example.zaphk.studenthelperapplication3.R;
public class MainActivity extends AppCompatActivity {
private NotesAdapter mAdapter;
private List<Note> notesList = new ArrayList<>();
private CoordinatorLayout coordinatorLayout;
private RecyclerView recyclerView;
private TextView noNotesView;
private DatabaseHelper db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_notes);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
coordinatorLayout = findViewById(R.id.coordinator_layout);
recyclerView = findViewById(R.id.recycler_view);
noNotesView = findViewById(R.id.empty_notes_view);
db = new DatabaseHelper(this);
notesList.addAll(db.getAllNotes());
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
showNoteDialog(false, null, -1);
}
});
mAdapter = new NotesAdapter(this, notesList);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(mLayoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.addItemDecoration(new MyDividerItemDecoration(this, LinearLayoutManager.VERTICAL, 16));
recyclerView.setAdapter(mAdapter);
toggleEmptyNotes();
/**
* On long press on RecyclerView item, open alert dialog
* with options to choose
* Edit and Delete
* */
recyclerView.addOnItemTouchListener(new RecyclerTouchListener(this,
recyclerView, new RecyclerTouchListener.ClickListener() {
@Override
public void onClick(View view, final int position) {
}
@Override
public void onLongClick(View view, int position) {
showActionsDialog(position);
}
}));
}
/**
* Inserting new note in db
* and refreshing the list
*/
private void createNote(String note) {
// inserting note in db and getting
// newly inserted note id
long id = db.insertNote(note);
// get the newly inserted note from db
Note n = db.getNote(id);
if (n != null) {
// adding new note to array list at 0 position
notesList.add(0, n);
// refreshing the list
mAdapter.notifyDataSetChanged();
toggleEmptyNotes();
}
}
/**
* Updating note in db and updating
* item in the list by its position
*/
private void updateNote(String note, int position) {
Note n = notesList.get(position);
// updating note text
n.setNote(note);
// updating note in db
db.updateNote(n);
// refreshing the list
notesList.set(position, n);
mAdapter.notifyItemChanged(position);
toggleEmptyNotes();
}
/**
* Deleting note from SQLite and removing the
* item from the list by its position
*/
private void deleteNote(int position) {
// deleting the note from db
db.deleteNote(notesList.get(position));
// removing the note from the list
notesList.remove(position);
mAdapter.notifyItemRemoved(position);
toggleEmptyNotes();
}
/**
* Opens dialog with Edit - Delete options
* Edit - 0
* Delete - 0
*/
private void showActionsDialog(final int position) {
CharSequence colors[] = new CharSequence[]{"Edit", "Delete"};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Choose option");
builder.setItems(colors, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
if (which == 0) {
showNoteDialog(true, notesList.get(position), position);
} else {
deleteNote(position);
}
}
});
builder.show();
}
/**
* Shows alert dialog with EditText options to enter / edit
* a note.
* when shouldUpdate=true, it automatically displays old note and changes the
* button text to UPDATE
*/
private void showNoteDialog(final boolean shouldUpdate, final Note note, final int position) {
LayoutInflater layoutInflaterAndroid = LayoutInflater.from(getApplicationContext());
View view = layoutInflaterAndroid.inflate(R.layout.note_dialog, null);
AlertDialog.Builder alertDialogBuilderUserInput = new AlertDialog.Builder(MainActivity.this);
alertDialogBuilderUserInput.setView(view);
final EditText inputNote = view.findViewById(R.id.note);
TextView dialogTitle = view.findViewById(R.id.dialog_title);
dialogTitle.setText(!shouldUpdate ? getString(R.string.lbl_new_note_title) : getString(R.string.lbl_edit_note_title));
if (shouldUpdate && note != null) {
inputNote.setText(note.getNote());
}
alertDialogBuilderUserInput
.setCancelable(false)
.setPositiveButton(shouldUpdate ? "update" : "save", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogBox, int id) {
}
})
.setNegativeButton("cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogBox, int id) {
dialogBox.cancel();
}
});
final AlertDialog alertDialog = alertDialogBuilderUserInput.create();
alertDialog.show();
alertDialog.getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Show toast message when no text is entered
if (TextUtils.isEmpty(inputNote.getText().toString())) {
Toast.makeText(MainActivity.this, "Enter note!", Toast.LENGTH_SHORT).show();
return;
} else {
alertDialog.dismiss();
}
// check if user updating note
if (shouldUpdate && note != null) {
// update note by it's id
updateNote(inputNote.getText().toString(), position);
} else {
// create new note
createNote(inputNote.getText().toString());
}
}
});
}
/**
* Toggling list and empty notes view
*/
private void toggleEmptyNotes() {
// you can check notesList.size() > 0
if (db.getNotesCount() > 0) {
noNotesView.setVisibility(View.GONE);
} else {
noNotesView.setVisibility(View.VISIBLE);
}
}
}
NotesAdapter.java
package com.example.zaphk.studenthelperapplication3.view;
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.text.Html;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;
import com.example.zaphk.studenthelperapplication3.calendar.database.Calendar;
import com.example.zaphk.studenthelperapplication3.database.model.Note;
import com.example.zaphk.studenthelperapplication3.R;
public class NotesAdapter extends RecyclerView.Adapter<NotesAdapter.MyViewHolder> {
private Context context;
private List<Note> notesList;
public class MyViewHolder extends RecyclerView.ViewHolder {
public TextView note;
public TextView dot;
public TextView timestamp;
public MyViewHolder(View view) {
super(view);
note = view.findViewById(R.id.note);
dot = view.findViewById(R.id.dot);
timestamp = view.findViewById(R.id.timestamp);
}
}
public NotesAdapter(Context context, List<Note> notesList) {
this.context = context;
this.notesList = notesList;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.note_list_row, parent, false);
return new MyViewHolder(itemView);
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
Note note = notesList.get(position);
holder.note.setText(note.getNote());
// Displaying dot from HTML character code
holder.dot.setText(Html.fromHtml("•"));
// Formatting and displaying timestamp
holder.timestamp.setText(formatDate(note.getTimestamp()));
}
@Override
public int getItemCount() {
return notesList.size();
}
/**
* Formatting timestamp to `MMM d` format
* Input: 2018-02-21 00:15:42
* Output: Feb 21
*/
private String formatDate(String dateStr) {
try {
SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = fmt.parse(dateStr);
SimpleDateFormat fmtOut = new SimpleDateFormat("MMM d");
return fmtOut.format(date);
} catch (ParseException e) {
}
return "";
}
}
activity_notes.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/coordinator_layout"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.zaphk.studenthelperapplication3.view.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main_timetable" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
app:srcCompat="@drawable/ic_add_white_24dp" />
</android.support.design.widget.CoordinatorLayout>
note_list_row.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/coordinator_layout"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.zaphk.studenthelperapplication3.view.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main_timetable" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
app:srcCompat="@drawable/ic_add_white_24dp" />
</android.support.design.widget.CoordinatorLayout>
content_main_timetable.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context=".activities.TimetableActivity"
tools:showIn="@layout/app_bar_main">
<android.support.v4.view.ViewPager
android:id="@+id/viewPager"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v4.view.ViewPager>
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@drawable/baseline_add_white_24"
tools:layout_editor_absoluteX="339dp"
tools:layout_editor_absoluteY="546dp" />
</FrameLayout>
