Attempt to invoke virtual method void android widget Button setOnClickListener android view View OnClickListener on a null object reference

Question

The problem is as follows  I have a login activity  in Android Studio  which worked fine a few days before  I don t remember changing anything but when I run this one the previous time the app closed right after I clicked the login button  The last thing indicated was the toast about pre-execution of AsyncTask  And I can t understand why there could be a NullPointerException  I have almost the same code for my signup activity and it works fine   Here is the log   05-28 16 04 52 395    1218-1232 system process V WindowManager  addAppToken  AppWindowToken 5d89eb token Token 23ccc93a ActivityRecord 2fe54865 u0 utanashati reminder  HomepageActivity t17    to stack 1 task 17 at 1 05-28 16 04 52 407  19927-19927 utanashati reminder D AndroidRuntime  Shutting down VM 05-28 16 04 52 408  19927-19927 utanashati reminder E AndroidRuntime  FATAL EXCEPTION  main     Process  utanashati reminder  PID  19927     java lang RuntimeException  Unable to start activity ComponentInfo utanashati reminder utanashati reminder HomepageActivity   java lang NullPointerException  Attempt to invoke virtual method  void android widget Button setOnClickListener android view View OnClickListener   on a null object reference             at android app ActivityThread performLaunchActivity ActivityThread java 2325              at android app ActivityThread handleLaunchActivity ActivityThread java 2390              at android app ActivityThread access 800 ActivityThread java 151              at android app ActivityThread H handleMessage ActivityThread java 1303              at android os Handler dispatchMessage Handler java 102              at android os Looper loop Looper java 135              at android app ActivityThread main ActivityThread java 5257              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 903              at com android internal os ZygoteInit main ZygoteInit java 698       Caused by  java lang NullPointerException  Attempt to invoke virtual method  void android widget Button setOnClickListener android view View OnClickListener   on a null object reference             at utanashati reminder HomepageActivity onCreate HomepageActivity java 55              at android app Activity performCreate Activity java 5990              at android app Instrumentation callActivityOnCreate Instrumentation java 1106              at android app ActivityThread performLaunchActivity ActivityThread java 2278                          at android app ActivityThread handleLaunchActivity ActivityThread java 2390                          at android app ActivityThread access 800 ActivityThread java 151                          at android app ActivityThread H handleMessage ActivityThread java 1303                          at android os Handler dispatchMessage Handler java 102                          at android os Looper loop Looper java 135                          at android app ActivityThread main ActivityThread java 5257                          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 903                          at com android internal os ZygoteInit main ZygoteInit java 698  05-28 16 04 52 410    1218-1232 system process W ActivityManager  Force finishing activity 1 utanashati reminder  HomepageActivity 05-28 16 04 52 411    1218-1232 system process W ActivityManager  Force finishing activity 2 utanashati reminder  LoginActivity   EDIT 1  I had my eyes opened  the problem is not with LoginActivity  but with HomepageActivity  Here is the code   import      public class HomepageActivity extends Activity implements AdapterView OnItemSelectedListener        protected EditText mAddTaskText      protected Spinner mPrioritySpinner      protected Button mAddTaskButton      protected int intPriority   0      protected String taskText      protected Timestamp taskTimestamp      protected Task userTask      protected JsonGenerator taskJSON        Override     protected void onCreate Bundle savedInstanceState                              Starts activity  The state can be restored from savedInstanceState         super onCreate savedInstanceState                                          Calls the superclass method  IMPORTANT          setContentView R layout activity homepage                                  Sets layout from activity homepage xml          mPrioritySpinner    Spinner  findViewById R id prioritySpinner             Creates an ArrayAdapter using the string array and a default spinner layout         ArrayAdapter lt CharSequence gt  adapter   ArrayAdapter createFromResource this                  R array priorityList  android R layout simple spinner item         Specifies the layout to use when the list of choices appears         adapter setDropDownViewResource android R layout simple spinner dropdown item          Applies the adapter to the spinner         mPrioritySpinner setAdapter adapter           mPrioritySpinner setOnItemSelectedListener this            mAddTaskText    EditText  findViewById R id addTaskEditText                Finds View by its id in  xml file         mAddTaskButton setOnClickListener new View OnClickListener                  Override             public void onClick View v                    Toast makeText HomepageActivity this   Done    Toast LENGTH LONG  show                     Calendar taskCalendar   Calendar getInstance                   Creates new calendar                 long taskTime   taskCalendar getTimeInMillis                   Gets time in milliseconds                 taskTimestamp   new Timestamp taskTime                         Creates new Timestamp                 taskText   mAddTaskText getText   toString                     Gets description of the task                  userTask setDate taskTimestamp                                 Sets date                 userTask setText taskText                                      Sets text                     Creating JsonGenerator                    ObjectMapper mapper   new ObjectMapper                    try                       mapper writeValue taskJSON  userTask                                     catch  IOException e                        Toast makeText HomepageActivity this   Could not create JSON   Toast LENGTH LONG  show                                          Getting out email and password                    String userPassword     EmailPassword  HomepageActivity this getApplication    getPassword                    String userEmail     EmailPassword  HomepageActivity this getApplication    getUserEmail                    Toast makeText HomepageActivity this  userEmail         userPassword  Toast LENGTH LONG  show                        HTTP stuff                    HttpPoster get   new HttpPoster                    get execute userEmail  userPassword  taskJSON toString                                          public int getData  String username  String password  String taskJSON            try               HttpPost httpPost   new HttpPost  http   something com     username     tasks                String dataToEncode   username         password              String encodedData   Base64 encodeToString dataToEncode getBytes    Base64 NO WRAP               httpPost setHeader  Authorization   encodedData                try                   StringEntity taskEntity   new StringEntity taskJSON   UTF-8                    httpPost setEntity taskEntity                             catch  UnsupportedEncodingException e                    Toast makeText HomepageActivity this   Unsupported encoding   Toast LENGTH LONG  show                               HttpClient client   new DefaultHttpClient                HttpResponse response   client execute httpPost               StatusLine statusLine   response getStatusLine                int statusCode   statusLine getStatusCode                if  statusCode    200                    return 1                            else if  statusCode    404    return 2                else if  statusCode    500    return 3                else if  statusCode    409    return 4                else   return statusCode                      catch  IOException e                e printStackTrace                      return 0             public void onItemSelected AdapterView lt   gt  parent  View view                                 int pos  long id            String priority   parent getItemAtPosition pos  toString                   Gets chosen priority         Toast makeText HomepageActivity this  priority  Toast LENGTH LONG  show            while     priority equals  Low        priority equals  Medium        priority equals  High                    Toast makeText HomepageActivity this   Something bad happened  Try to choose again   Toast LENGTH LONG  show                      if  priority equals  Low                  intPriority   0                    else if  priority equals  Medium                  intPriority   1                    else if  priority equals  High                  intPriority   2                    userTask setPriority intPriority                                           Sets chosen priority            public void onNothingSelected AdapterView lt   gt  parent            userTask setPriority intPriority                                           Sets default priority   0              public class HttpPoster extends AsyncTask lt String  Void  Integer gt              Override         protected void onPreExecute                 super onPreExecute                        Override         protected Integer doInBackground String    params                return getData params 0   params 1   params 3                        Override         protected void onPostExecute Integer result                super onPostExecute result               if  result    1                    Toast makeText HomepageActivity this   Login successful   Toast LENGTH LONG  show                    Intent takeUserHome   new Intent HomepageActivity this  HomepageActivity class                   startActivity takeUserHome                             else if  result    2                    Toast makeText HomepageActivity this   No such user   Toast LENGTH LONG  show                              else if  result    3                    Toast makeText HomepageActivity this   Internal server error  unable to send email   Toast LENGTH LONG  show                              else if  result    4                    Toast makeText HomepageActivity this   Task already exists   Toast LENGTH LONG  show                              else                   Toast makeText HomepageActivity this  result toString    Toast LENGTH LONG  show                                      And XML file    lt RelativeLayout xmlns android  http   schemas android com apk res android      xmlns tools  http   schemas android com tools      android layout width  match parent      android layout height  match parent      android paddingLeft   dimen activity horizontal margin      android paddingRight   dimen activity horizontal margin      android paddingTop   dimen activity vertical margin      android paddingBottom   dimen activity vertical margin      tools context  utanashati testapp HomepageActivity  gt        lt EditText         android layout width  match parent          android layout height  wrap content          android hint  Add a new task             android id    id addTaskEditText          android nestedScrollingEnabled  false          android minLines  1          android maxLines  1    gt        lt Spinner         android layout width  match parent          android layout height  wrap content          android id    id prioritySpinner          android layout alignRight    id addTaskButton          android layout alignEnd    id addTaskButton          android layout below    id addTaskEditText    gt        lt Button         android layout width  match parent          android layout height  wrap content          android text  Add task          android id    id addTaskButton          android layout below    id prioritySpinner          android layout centerHorizontal  true    gt    lt  RelativeLayout gt

User · Answer

Check whether you have matching IDs in both Java and XML

User · Answer

Just define the button as lateinit var at top of your class    lateinit var buttonOk  Button   When you want to use a button in another layout you should define it in that layout  For example if you want to use button in layout which name is  dialogview   you should write    buttonOk   dialogView findViewById lt Button gt  R id buttonOk    After this you can use setonclicklistener for the button and you won t have any error  You can see correct answer of this question  Android Kotlin findViewById must not be null

User · Answer

Placing setOnClickListener in onStart method solved the problem for me  Checkout  quot Android Lifecycle concept quot  for further clarification

User · Answer

Got the same error  CHECK THIS   MINOR SILLY MISTAKE check findviewbyid R id yourID   If you have put the id correct or not

User · Answer

Check out this solution  It worked for me      Check the id of the button for which the error is raised   it may be the same in any one of the  other page in your app  If yes  then change the id of them and then the app runs perfectly   I was having two same button id s in two different XML codes    I changed the id  Now it runs perfectly   Hope it works

User · Answer

That true Mustafa    its working  its point to two layout      setContentView R layout your layout  v23 your layout     You should take Button both activity layout    solve this problem successfully

User · Answer

mAddTaskButton setOnClickListener new View OnClickListener    you have a click listner but you haven t initialized the mAddTaskButton with your layout binding

User · Answer

Make sure that while using   Button  varName   findViewById  btID    you put in the right  btID   I accidentally put in the id of a button from another similar activity and it showed the same error  Hope it helps

User · Answer

It seems the button you are invoking is not in the layout you are using in setContentView R layout your layout  Check it

User · Answer

mAddTaskButton is null because you never initialize it with   mAddTaskButton    Button  findViewById R id addTaskButton     before you call mAddTaskButton setOnClickListener

User · Answer

i had the same problem and it seems like i didn t initiate the button used with click listener  in other words id didn t te

[java] Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

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