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How to write Shared preference Code that uses firebase for User authentication?

How do I write Shared-preference Code that is using Firebase for User authentication and the data that is saved by a user is only accessible for them?
My current application Saves a note and displays it which is the main thing needed in my project but when a user logs out and new user logs in he/she can also view the data so the data is not private. My sir suggested to make nodes for users using shared preference but i couldn't find any solutions
HomeActivity:
public class HomeActivity extends AppCompatActivity {
EditText Descriptionholder;
Button Savebtn;
DatabaseReference DatabaseNote;
ListView listViewNotes;
List<PrivateNote> privateNoteList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
DatabaseNote = FirebaseDatabase.getInstance().getReference("privatenote");
Descriptionholder = findViewById(R.id.description2);
Savebtn = findViewById(R.id.buttonsave);
listViewNotes= findViewById(R.id.listViewPrivate);
privateNoteList = new ArrayList<>();
Savebtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
addnote();
}
});
listViewNotes.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
#Override
public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l) {
PrivateNote privateNote = privateNoteList.get(i); //confusion
showUpdateDialog(privateNote.getNoteId(),privateNote.getNoteDescription());
return false;
}
});
}
public boolean onCreateOptionsMenu (Menu menu){
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.side, menu);
return true;
}
#Override
public boolean onOptionsItemSelected (MenuItem item){
switch (item.getItemId()) {
case R.id.item1:
FirebaseAuth.getInstance().signOut();
finish();
startActivity(new Intent(new Intent(this, MainActivity.class)));
Toast.makeText(this, "Logged out ", Toast.LENGTH_SHORT).show();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
#Override
protected void onStart() {
super.onStart();
DatabaseNote.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
privateNoteList.clear();
for (DataSnapshot privateSnapshot: dataSnapshot.getChildren() ){
PrivateNote privateNote = privateSnapshot.getValue(PrivateNote.class);
privateNoteList.add(privateNote);
}
PrivateList adapter = new PrivateList(HomeActivity.this,privateNoteList);
listViewNotes.setAdapter(adapter);
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
private void showUpdateDialog(final String noteId, String noteDescription){
AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(this);
LayoutInflater inflater = getLayoutInflater();
final View dialogview = inflater.inflate(R.layout.update_dialouge,null);
dialogBuilder.setView(dialogview);
final EditText editDescription = dialogview.findViewById(R.id.editDescription);
final Button buttonUpdate = dialogview.findViewById(R.id.buttonUpdate);
final Button buttonDelete = dialogview.findViewById(R.id.buttonDelete);
dialogBuilder.setTitle("Updating Note: " +noteDescription);
final AlertDialog alertDialog = dialogBuilder.create();
alertDialog.show();
buttonUpdate.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String description = editDescription.getText().toString().trim();
if (TextUtils.isEmpty(description)){
editDescription.setError(" New information required");
return;
}
updatePrivateNote(noteId,description);
alertDialog.dismiss();
}
});
buttonDelete.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
deletePrivateNote(noteId);
}
});
}
private void deletePrivateNote(String noteId) {
DatabaseReference drPrivateNote = FirebaseDatabase.getInstance().getReference("privatenote").child(noteId);
drPrivateNote.removeValue();
Toast.makeText(this, " Note Deleted", Toast.LENGTH_SHORT).show();
}
private boolean updatePrivateNote(String id,String description){
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("privatenote").child(id);
PrivateNote privateNote = new PrivateNote(id,description);
databaseReference.setValue(privateNote);
Toast.makeText(this, " Note Updated", Toast.LENGTH_SHORT).show();
return true;
}
private void addnote () {
String description = Descriptionholder.getText().toString().trim();
if (!TextUtils.isEmpty(description)){
//generated unique number for id
String id = DatabaseNote.push().getKey();
PrivateNote pNote = new PrivateNote(id, description);
DatabaseNote.child(id).setValue(pNote); //pNote value added in id
Toast.makeText(this, "Note added", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(this, " Please Enter a note ", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onBackPressed() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure you want to exit?")
.setCancelable(false)
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
FirebaseAuth.getInstance().signOut();
finish();
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}
Adapter:
public class PrivateList extends ArrayAdapter<PrivateNote> {
private Activity context;
private List<PrivateNote> privateNoteList;
public PrivateList(Activity context, List<PrivateNote> privateNoteList){
super(context, R.layout.list_layout,privateNoteList);
this.context =context;
this.privateNoteList=privateNoteList;
}
#NonNull
#Override
public View getView(int position, #Nullable View convertView, #NonNull ViewGroup parent) {
LayoutInflater inflater = context.getLayoutInflater();
View listViewItem = inflater.inflate(R.layout.list_layout,null,true);
TextView textViewDescription = listViewItem.findViewById(R.id.TextViewDescription);
PrivateNote privateNote = privateNoteList.get(position);
textViewDescription.setText(privateNote.getNoteDescription());
return listViewItem;
}
}
PrivateNote:
public class PrivateNote {
public String noteId;
public String noteDescription;
public PrivateNote(){
}
PrivateNote(String noteId, String noteDescription){
this.noteId = noteId;
this.noteDescription=noteDescription;
}
String getNoteId()
{
return noteId;
}
String getNoteDescription()
{
return noteDescription;
}
}

In Firebase, there are two things,
FirebaseDatabase
FirebaseAuth
Usually, in almost all the apps, user data is stored in the FirebaseDatabase under the key, that is generated while creating a new user in your Firebase app.
So, for example, your database structure will look like this.
-Your_main_database
|____UserId_Of_FirebaseUser
|____stuff_related_to_user
|____More stuff related to user
So, you create a new user in FirebaseAuth, you can find more about it below:
Firebase Custom Auth.
Then, after creating a new user, you create child nodes under your database with the key=userId of your current logged in user.
eg. In your addNote function, the id variable will be equal to
String id = FirebaseAuth.getInstance().getCurrentUser().getUid();
Currently, you're using Push keys which are generated based on Timestamp, which you won't be able to associate with user unless you add a key inside your note object which stored current username, and then find all the child nodes that contain that username, but in that case, your data won't be organized at all.
Then, after you create a node with userId under your main database, you can then push new notes created by your user inside the userId with the push() function. So your database structure will look like below.
___
|
|__users
|__uniqueUserId
| |__note1
| |__note2
|__uniqueUserId2
|__note1
|__note2
|__note3
Next time whenever you want to fetch user created notes, you log in the user, get his ID, and then find the notes corresponding to that ID.
I don't see how you can fit SharedPreferences in there, before there is also function to cache data offline in Firebase once it is loaded.
Securing the notes:
If you implement the database like I said above, you'll be very easily able to secure your database.
Common Database Rules.
If you implement everything correctly like I told, you'll be able to secure your database with the fourth set of rules from above rules.

Since you are using firebase authentication, then you can retrieve the userId, and create the following database:
notes
userId
note : "todo"
description : "study"
Then you can do:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("notes");
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
String userId = user.getUid();
ref.orderByKey().equalTo(userId).addValueEventListener(new ValueEventListener() {...}
This way you would retrieve the data of the currently logged in user only.

Method called inside interface method returns null

I created an interface so I can communicate between a dialogue and a fragment.
Goal: When the user selects anything from the dialogue it should display it on a text view.
In this interface, I created an interface method, called in the main activity and passed the value the user selected in the dialogue. Along with the user selected value, in my fragment, I created a method that will set the text view to that value. However, whenever I call that method it always returns null.
I did plenty of testing with logs and found that the values being passed through my method is NOT null, everything seems to work the exact way I want it to which is odd. What confuses me even more, is that this method isn't even running, it immediately returns null before executing the code inside which is really strange to me.
Dialog Code:
public String users_time;
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
final String time_options[] = {"10", "20", "30", "40", "50", "60", "70", "80", "90"}; // Since we know how many options there are in the array we use an array instead of an arraylist
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setTitle("Choose the time");
builder.setSingleChoiceItems(time_options, -1, new DialogInterface.OnClickListener() { // check items = what index is auto selected in the dialog, use -1 bc you dont want that
#Override
public void onClick(DialogInterface dialog, int which) { // which = Index in the array
CharSequence time = time_options[which];
Log.i("this" ,"LOG 1 dialogsTime retusn" + time);
listener.onDialogInput(time);
users_time = time_options[which];
int usersTime = Integer.valueOf(users_time);
listener.grabTime(usersTime);
}
});
builder.setPositiveButton("Set Time", new DialogInterface.OnClickListener() { // positive = Ok or continue
#Override
public void onClick(DialogInterface dialog, int which) {
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() { // Negative = Cancel or stop
#Override
public void onClick(DialogInterface dialog, int which) {
}
});
return builder.create(); // always return this at the end
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof DiaglogListener) {
listener = (DiaglogListener) context;
}
else {
throw new RuntimeException(context.toString()
+ " must implement DiaglogListener");
}
}
#Override
public void onDetach() {
super.onDetach();
listener = null;
}
}
Main Activity Interface Method:
#Override
public void onDialogInput(CharSequence dialogsTime) {
Fragment1_timer frag1 = new Fragment1_timer();
Log.i("this" ,"LOG 2 runs successfully");
try {
frag1.setDialogTime(dialogsTime);
} catch (Exception e){
Toast.makeText(this, "Null error :/", Toast.LENGTH_SHORT).show();
}
}
Fragment Method:
public void setDialogTime(CharSequence time){
Log.i("this" ,"LOG 3 ran successfully");
text_view_time.setText(time + ":00");
}

You can't use onAttach method for Fragment to DialogFragment communication.
you will have to use "setTargetFragment" & "getTargetFragment" for that.
you can refer this answer. https://stackoverflow.com/a/32323822/9792247

Android studio recylerview in fragment using data from firestore [duplicate]

This question already has an answer here:
How to display data from Firestore in a RecyclerView with Android?
(1 answer)
Closed 4 years ago.
I am currently developing a mobile app in Android Studio. I have a collection in Firebase firestore called Leagues. When I open a fragment from the navigation drawer, the recyclerview is empty. I have two buttons at the top of the layout, both of which open an alert dialog. When I click on either of the buttons and click on the box to start entering text, the leagues magically appear in the recyclerview! Ideally I would like them to appear when the fragment is first opened. To give a bit more context I have a method which fetches the leagues from the collection in Firebase, but having debugged it I've found that this initially returns an empty list. Only when the edittext box in the alert dialog is pressed does the list fill up. Can anyone think why this might be the case?
Thanks in advance
Edit:
public class LeaguesFragment extends Fragment {
Button buttonCreateLeague;
Button buttonJoinLeague;
View view;
FirebaseFirestore firestore;
private String leagueID;
private String userID;
private String leagueName;
private String username;
TextView textViewMyLeagues;
RecyclerView recyclerView;
private List<Leagues> leaguesList;
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_leagues, container, false);
recyclerView = (RecyclerView) view.findViewById(R.id.leaguesList);
RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(getContext(), leaguesList);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
recyclerView.setAdapter(recyclerViewAdapter);
buttonCreateLeague = (Button) view.findViewById(R.id.buttonCreateLeague);
buttonJoinLeague = (Button) view.findViewById(R.id.buttonJoinLeague);
textViewMyLeagues = (TextView) view.findViewById(R.id.textViewMyLeagues);
firestore = FirebaseFirestore.getInstance();
userID = FirebaseAuth.getInstance().getUid();
firestore.collection("users").document(userID).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if(task.isSuccessful()) {
DocumentSnapshot documentSnapshot = task.getResult();
username = documentSnapshot.getString("name");
}
}
});
buttonCreateLeague.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
leagueID = CreateLeagueID.randomString(6);
AlertDialog.Builder alert = new AlertDialog.Builder(getContext());
alert.setMessage("Enter league name");
final EditText input = new EditText(getContext());
alert.setView(input);
alert.setPositiveButton("Confirm", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
leagueName = input.getText().toString().trim();
createLeague(leagueID, leagueName);
addUserToLeague(leagueID, username);
addLeagueToUser(leagueID, userID, leagueName);
}
});
alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// Cancelled.
}
});
alert.show();
}
});
buttonJoinLeague.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
AlertDialog.Builder alert = new AlertDialog.Builder(getContext());
alert.setMessage("Enter league code");
final EditText input = new EditText(getContext());
alert.setView(input);
alert.setPositiveButton("Confirm", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
leagueID = input.getText().toString().trim();
firestore.collection("leagues").document(leagueID).collection("members").document(username).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if(task.isSuccessful()) {
DocumentSnapshot documentSnapshot = task.getResult();
if(documentSnapshot.exists()) {
Toast.makeText(getActivity(), "Already part of this league", Toast.LENGTH_SHORT).show();
}
else {
firestore.collection("leagues").document(leagueID).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot documentSnapshot = task.getResult();
if (documentSnapshot.exists()) {
leagueName = documentSnapshot.getString("leagueName");
addUserToLeague(leagueID, username);
addLeagueToUser(leagueID, userID, leagueName);
}
else {
Toast.makeText(getActivity(), "That league does not exist", Toast.LENGTH_SHORT).show();
}
}
}
});
}
}
}
});
}
});
alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// Cancelled.
}
});
alert.show();
}
});
return view;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
leaguesList = new ArrayList<>();
firestore = FirebaseFirestore.getInstance();
userID = FirebaseAuth.getInstance().getUid();
firestore.collection("users").document(userID).collection("leagues").addSnapshotListener(new EventListener<QuerySnapshot>() {
#Override
public void onEvent(#javax.annotation.Nullable QuerySnapshot queryDocumentSnapshots, #javax.annotation.Nullable FirebaseFirestoreException e) {
if(e != null) {
Log.d(TAG, "Error : " + e.getMessage());
}
for(DocumentChange doc: queryDocumentSnapshots.getDocumentChanges()) {
if(doc.getType() == DocumentChange.Type.ADDED) {
//leagueID = doc.getDocument().getString("leagueID");
//leagueName = doc.getDocument().getString("leagueName");
Leagues leagues = doc.getDocument().toObject(Leagues.class);
leaguesList.add(leagues);
}
}
}
});
}

having debugged it I've found that this initially returns an empty list.
Yes, this the normal behaviour. You cannot use now something that hasn't been loaded yet. With other words, you cannot simply create the leaguesList variable as global variable and use it outside the onEvent() method because it will always be empty due the asynchronous behaviour of this method. This means that by the time you are trying to use that list outside that method, the data hasn't finished loading yet from the database and that's why is not accessible. A quick solve for this problem would be to use leaguesList list only inside the onEvent() method, otherwise I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. You can also take a look at this video for a better understanding.

Maybe the problem is your leaguesList still empty when onCreateView is trigger. And when onEvent from firestore trigger you not notify data set change the adapter.

NullPointerException when using database object [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
I'm new to Android, and i've got some issues.
It looks like it's saying DB.EmployeeOperations.open() is having an null object passed to it, but I'm not sure.
Where I missed a step?
Any help is appreciated.
Thanks in advance.
Logcat:
* 06-10 16:10:52.605 17203-17203/com.androidtutorialpoint.employeemanagementsystem E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.androidtutorialpoint.employeemanagementsystem, PID: 17203
java.lang.RuntimeException: Unable to resume activity {com.androidtutorialpoint.employeemanagementsystem/com.androidtutorialpoint.employeemanagementsystem.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.androidtutorialpoint.employeemanagementsystem.DB.EmployeeOperations.open()' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3019)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3050)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2425)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5294)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.androidtutorialpoint.employeemanagementsystem.DB.EmployeeOperations.open()' on a null object reference
at com.androidtutorialpoint.employeemanagementsystem.MainActivity.onResume(MainActivity.java:148)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1257)
at android.app.Activity.performResume(Activity.java:6076)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3008)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3050)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2425)
at android.app.ActivityThread.access$900(ActivityThread.java:154)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
Java Code:
public class MainActivity extends AppCompatActivity{
private Button addEmployeeButton;
private Button editEmployeeButton;
private Button deleteEmployeeButton;
private Button viewAllEmployeeButton;
private EmployeeOperations employeeOps;
private static final String EXTRA_EMP_ID = "com.androidtutorialpoint.empId";
private static final String EXTRA_ADD_UPDATE = "com.androidtutorialpoint.add_update";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addEmployeeButton = (Button) findViewById(R.id.button_add_employee);
editEmployeeButton = (Button) findViewById(R.id.button_edit_employee);
deleteEmployeeButton = (Button) findViewById(R.id.button_delete_employee);
viewAllEmployeeButton = (Button)findViewById(R.id.button_view_employees);
addEmployeeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this,AddUpdateEmployee.class);
i.putExtra(EXTRA_ADD_UPDATE, "Add");
startActivity(i);
}
});
editEmployeeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
getEmpIdAndUpdateEmp();
}
});
deleteEmployeeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
getEmpIdAndRemoveEmp();
}
});
viewAllEmployeeButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this, ViewAllEmployees.class);
startActivity(i);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.employee_menu, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.menu_item_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void getEmpIdAndUpdateEmp(){
LayoutInflater li = LayoutInflater.from(this);
View getEmpIdView = li.inflate(R.layout.dialog_get_emp_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_emp_id.xml to alertdialog builder
alertDialogBuilder.setView(getEmpIdView);
final EditText userInput = (EditText) getEmpIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
// get user input and set it to result
// edit text
Intent i = new Intent(MainActivity.this,AddUpdateEmployee.class);
i.putExtra(EXTRA_ADD_UPDATE, "Update");
i.putExtra(EXTRA_EMP_ID, Long.parseLong(userInput.getText().toString()));
startActivity(i);
}
}).create()
.show();
}
public void getEmpIdAndRemoveEmp(){
LayoutInflater li = LayoutInflater.from(this);
View getEmpIdView = li.inflate(R.layout.dialog_get_emp_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_emp_id.xml to alertdialog builder
alertDialogBuilder.setView(getEmpIdView);
final EditText userInput = (EditText) getEmpIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
// get user input and set it to result
// edit text
employeeOps = new EmployeeOperations(MainActivity.this);
employeeOps.removeEmployee(employeeOps.getEmployee(Long.parseLong(userInput.getText().toString())));
Toast t = Toast.makeText(MainActivity.this,"Employee removed successfully!",Toast.LENGTH_SHORT);
t.show();
}
}).create()
.show();
}
#Override
protected void onResume() {
super.onResume();
employeeOps.open();
}
#Override
protected void onPause() {
super.onPause();
employeeOps.close();
}
}

The problem is you're calling employeeOps.open() in onResume(), but employeeOps is not instantiated yet, it's value is still null.
Take a look at the Activity lifecycle.
As you can see, when an Activity gets created two methods get called before onResume(): onCreate() and onStart().
If you would like to call the open() method of EmployeeOperations in onResume(), you need to have an instance of it by then.
Call the following in onCreate():
employeeOps = new EmployeeOperations(this);

Your problem is a misunderstanding of the Android lifecycle. Specifically, from that resource,
Once the onCreate() finishes execution, the system calls the onStart() and onResume() methods in quick succession.
What this means for you is that onResume() triggers before you ever set employeeOps to a non-null value. You're only initializing it in response to a button press, but your Activity is only visible for a very short duration before onResume is triggered.

Android error at Intent command [closed]

Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers.
This question was caused by a typo or a problem that can no longer be reproduced. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers.
Closed 6 years ago.
Improve this question
I'm having trouble with my code. When I click on the Title "New Profile" a new Activity has to start but when I click, an alert is shown: "Unfortunately %AppName% has stopped.".
Here is log of Android Monitor
--------- beginning of crash
05-17 01:19:54.545 2568-2568/com.example.felipe.myappproject E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.felipe.myappproject, PID: 2568
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.felipe.myappproject/com.example.felipe.myappproject.NewProfileActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
at android.content.ComponentName.<init>(ComponentName.java:128)
at android.content.Intent.<init>(Intent.java:4449)
at com.example.felipe.myappproject.NewProfileActivity.<init>(NewProfileActivity.java:14)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
And here my NewProfileActivity.java
public class NewProfileActivity extends AppCompatActivity {
EditText profile, password, confirmpass;
Intent insert = new Intent(NewProfileActivity.this, MainActivity.class);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_new_profile);
}
public void backMain(View v){
startActivity(back);
}
public void insertData(View v) {
profile = (EditText) findViewById(R.id.profileName);
password = (EditText) findViewById(R.id.password);
confirmpass = (EditText) findViewById(R.id.confirmPassword);
insert.putExtra("profile", profile.getText().toString());
insert.putExtra("password", password.getText().toString());
insert.putExtra("profile", confirmpass.getText().toString());
compare(password.getText().toString(), confirmpass.getText().toString());
}
public void compare(String x, String y){
final AlertDialog alert = new AlertDialog.Builder(NewProfileActivity.this).create();
if(x.equals(y)){
alert.setTitle("New Profile!");
alert.setMessage("Profile "+profile+" registered");
alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
}
);
startActivity(insert);
} else {
alert.setTitle("Ops...");
alert.setMessage("Passwords don't macth");
alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
}
);
}
}
}
I can't find what I am doing wrong. I tried to simplify the code by removing everything except the "public void backMain(View v)" but I still get the same problem.

As per #MikeM's comment, you are initializing your Intent at the very beginning, where even the class that you are passing as a parameter isn't fully initialized yet.
You should simply just initialize right before you would use it like so:
public class NewProfileActivity extends AppCompatActivity {
EditText profile, password, confirmpass;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_new_profile);
}
public void backMain(View v) {
// startActivity(back);
}
public void insertData(View v) {
profile = (EditText) findViewById(R.id.profileName);
password = (EditText) findViewById(R.id.password);
confirmpass = (EditText) findViewById(R.id.confirmPassword);
compare(password.getText().toString(), confirmpass.getText().toString());
}
public void compare(String x, String y) {
final AlertDialog alert = new AlertDialog.Builder(NewProfileActivity.this).create();
if (x.equals(y)) {
alert.setTitle("New Profile!");
alert.setMessage("Profile " + profile + " registered");
alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
}
);
// CODES Transferred here ====
Intent insert = new Intent(NewProfileActivity.this, MainActivity.class);
insert.putExtra("profile", profile.getText().toString());
insert.putExtra("password", password.getText().toString());
insert.putExtra("profile", confirmpass.getText().toString());
// CODES Transferred here ====
startActivity(insert);
} else {
alert.setTitle("Ops...");
alert.setMessage("Passwords don't macth");
alert.setButton(AlertDialog.BUTTON_NEUTRAL, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
}
);
}
}
}
Cheers! :D