App Crashing When Clicking on button to open a fragment dialog

Question

I'm building an app that opens a dialog of the calendar. Every time I press the button it crashes the app. Here's the console messages I get:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.mycontactlist.DatePickerDialog.onCreateView(DatePickerDialog.java:41) at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600) at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881) at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238) at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303) at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439) at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079) at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869) at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824) at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727) at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150) at android.os.Handler.handleCallback(Handler.java:938) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:223) at android.app.ActivityThread.main(ActivityThread.java:7656) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) I/Process: Sending signal. PID: 9726 SIG: 9 Disconnected from the target VM, address: 'localhost:61100', transport: 'socket'

Here's the code to the button

`private void initChangeDateButton(){
        Button changeDate = findViewById(R.id.btnBirthday);
        changeDate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentManager fm = getSupportFragmentManager();
                DatePickerDialog datePickerDialog = new DatePickerDialog();
               datePickerDialog.show(fm,"DatePick");
            }
        });

Here's the code to the datepicker dialog

public class DatePickerDialog extends DialogFragment {
    Calendar selectedDate;

            public interface SaveDateListener{
        void didFinishDatePickerDialog(Calendar selectedTime);
            }
            public DatePickerDialog(){

            }
            @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        final View view = inflater.inflate(R.layout.select_date, container);
    getDialog().setTitle("Select Date");
    selectedDate = Calendar.getInstance(TimeZone.getDefault());
    final CalendarView cv = view.findViewById(R.id.calendarView);
    cv.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
        @Override
        public void onSelectedDayChange(@NonNull CalendarView view, int year, int month, int day) {
            selectedDate.set(year,month,day);
        }
    });
    Button saveButton= view.findViewById(R.id.buttonSave);
    saveButton.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view){
            saveItem(selectedDate);
        }
    });
                Button cancelButton= view.findViewById(R.id.buttonCancel);
                saveButton.setOnClickListener(new View.OnClickListener(){
                    @Override
                    public void onClick(View view){
                        getDialog().dismiss();
                    }
                });
                return view;
            }
            private void saveItem(Calendar selectedTime){
        SaveDateListener activity = (SaveDateListener) getActivity();
        activity.didFinishDatePickerDialog(selectedTime);
        getDialog().dismiss();
            }
}

select_date Layout

LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:gravity="end">

    <CalendarView
        android:id="@+id/calendarView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <LinearLayout
        style="?android:attr/borderlessButtonStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/buttonCancel"
            style="?android:attr/borderlessButtonStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/cancel"
            android:textColor="@color/dialog_button_color"
            />

        <Button
            android:id="@+id/buttonSelect"
            style="?android:attr/borderlessButtonStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/select"
            android:textColor="@color/dialog_button_color"
            />
    </LinearLayout>
</LinearLayout>

I appreciate any help

Answer 1

Your code has

Button saveButton= view.findViewById(R.id.buttonSave);

But your XML has

<Button
    android:id="@+id/buttonSelect"

Note how the IDs don't match - that's why your saveButton variable is always null. You'll need to change one of those so that they match (it doesn't matter which one you choose, just that they match).