App Thread Crash

[Paul Jose]

I am trying to create a thread in an android application to keep checking my firebase database to check if an otp value has been put in the child value of a node. But it keeps crashing as soon as I start the application. This is my code so far.

//Thread check otp
Thread t = new Thread() {
@override
public void run() {
while(!isInterrupted()) {
try {
Thread.sleep(5000);
runOnUiThread(new Runnable() {
@override
public void run() {
//check OTP if present on database
FirebaseDatabase.getInstance().getReference().child("Keys")
.addListenerForSingleValueEvent(new ValueEventListener() {
@override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Subjects keys = snapshot.getValue(Subjects.class);
//System.out.println(user.email);
Intent i = new Intent(getApplicationContext(), markAttendance.class);
i.putExtra("otp",keys.otpcode);
i.putExtra("subid", keys.subjectId);
finish();
startActivity(i);

}
}
@override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});

} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};

t.start();

 

[v777779]

Please provide error log and may be more code about calling activity.
I tested your code without access to Firebase, it works fine.

 

[Paul Jose]

05-08 04:50:53.613 28585-28585/com.example.vdntd.attendancemanager E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.vdntd.attendancemanager, PID: 28585
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.vdntd.attendancemanager/com.example.vdntd.attendancemanager.markAttendance}: java.lang.NullPointerException: toCopy == null
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2924)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
Caused by: java.lang.NullPointerException: toCopy == null
at java.lang.StringFactory.newStringFromString(Native Method)
at com.example.vdntd.attendancemanager.markAttendance.onCreate(markAttendance.java:18)
at android.app.Activity.performCreate(Activity.java:6912)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6692)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

 

[Paul Jose]

class otpThread extends Thread {
@override
public void run() {

boolean running = true;
while(running==true) {

//final DatabaseReference databaseSubjects;
final FirebaseUser user = firebaseAuth.getCurrentUser();

//check OTP if present on database
FirebaseDatabase.getInstance().getReference().child("Keys")
.addListenerForSingleValueEvent(new ValueEventListener() {
@override
public void onDataChange(DataSnapshot dataSnapshot) {
for (final DataSnapshot snapshot : dataSnapshot.getChildren()) {
final Subjects keys = snapshot.getValue(Subjects.class);
//System.out.println(user.email);

FirebaseDatabase.getInstance().getReference("Users").child(user.getUid()).child("Subjects").addListenerForSingleValueEvent(new ValueEventListener() {
@override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()) {
for(DataSnapshot snapshot1 : dataSnapshot.getChildren()){
Subjects studentside = snapshot1.getValue(Subjects.class);

if((studentside.getSubjectId() == keys.subjectId) && (keys.otpcode != "0")) {
Intent i = new Intent(getApplicationContext(), markAttendance.class);
i.putExtra("otp",keys.otpcode);
i.putExtra("subid", keys.subjectId);
finish();
startActivity(i);
}
}
}

}

@override
public void onCancelled(DatabaseError databaseError) {

}
});


}
}
@override
public void onCancelled(DatabaseError databaseError) {
}
});
}
}
}

otpThread thread = new otpThread();
thread.start();


new code but it keeps hanging

 

[v777779]

It says that problem is with MarkAttendance.class
Please provide code of classes Subjects,class, MarkAttendance.class and JSON file of couple of records of your FirebaseDatabase.