Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
The problem is as follows. I have a login activity (in Android Studio) which worked fine a few days before. I don't remember changing anything but when I run this one the previous time the app closed right after I clicked the login button. The last thing indicated was the toast about pre-execution of AsyncTask. And I can't understand why there could be a NullPointerException. I have almost the same code for my signup activity and it works fine.
Here is the log:
05-28 16:04:52.395 1218-1232/system_process V/WindowManager﹕ addAppToken: AppWindowToken{5d89eb token=Token{23ccc93a ActivityRecord{2fe54865 u0 utanashati.reminder/.HomepageActivity t17}}} to stack=1 task=17 at 1
05-28 16:04:52.407 19927-19927/utanashati.reminder D/AndroidRuntime﹕ Shutting down VM
05-28 16:04:52.408 19927-19927/utanashati.reminder E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: utanashati.reminder, PID: 19927
java.lang.RuntimeException: Unable to start activity
ComponentInfo{utanashati.reminder/utanashati.reminder.HomepageActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$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<CharSequence> 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<?> 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<?> parent) {
userTask.setPriority(intPriority); // Sets default priority ("0")
}
public class HttpPoster extends AsyncTask<String, Void, Integer> {
@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:
<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">
<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" />
<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" />
<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" />
</RelativeLayout>
It seems the button you are invoking is not in the layout you are using in setContentView(R.layout.your_layout)
Check it.
mAddTaskButton is null because you never initialize it with:
mAddTaskButton = (Button) findViewById(R.id.addTaskButton);
before you call mAddTaskButton.setOnClickListener().
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
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
Check whether you have matching IDs in both Java and XML