Fixing Android NullPointerException

Question

i am creating an android app right, but every time I try to run it, I get a NullPointerException at line 2. What could be causing this? I for sure have the spinner in my build.xml file. When you call an object like this is it not getting initialized?

public void onStart(){

    spnLocale = (Spinner)findViewById(R.id.spinner1); //1

    spnLocale.setOnItemSelectedListener(new OnSelectListener()); //2

}
public static class MainSectionFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    public static final String ARG_SECTION_NUMBER = "section_number";

    public MainSectionFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        if(getArguments().getInt(ARG_SECTION_NUMBER)==1){
            View rootView = inflater.inflate(R.layout.browse_layout,
                container, false);
            Spinner spnLocale = (Spinner)findViewById(R.id.spinner1);


            spnLocale.setOnItemSelectedListener(new OnSelectListener());
            return rootView;

        }

        else {//if(getArguments().getInt(ARG_SECTION_NUMBER) == 3){
            View rootView = inflater.inflate(R.layout.fragment_main_dummy,
                    container, false);
            TextView dummyTextView = (TextView) rootView
                    .findViewById(R.id.section_label);
            dummyTextView.setText("help screen");
            return rootView;

        }

    }
}

Here is my xml:

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal" >

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="154dp"
        android:layout_height="wrap_content"
        android:entries="@array/state_array"
        android:prompt="@string/state_prompt" />

    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        />

</LinearLayout>

Here is my log :

03-22 03:40:17.242: E/AndroidRuntime(2101): Caused by: java.lang.NullPointerException 
03-22 03:40:17.242: E/AndroidRuntime(2101): at com.XXXX.list.MainActivity.onStart(MainActivity.java:175)
03-22 03:40:17.242: E/AndroidRuntime(2101): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
03-22 03:40:17.242: E/AndroidRuntime(2101): at android.app.Activity.performStart(Activity.java:5241)
03-22 03:40:17.242: E/AndroidRuntime(2101): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168) –  

Answer 1

the problem was I was using swipe Tabs, so I had to use rootView.findViewbyId() instead of just findviewbyID

Answer 2

You need to set Adapter to spinner before you can use onItemSelected Listener... this might help you

@Override
    protected void onStart() {
        // TODO Auto-generated method stub
        super.onStart();

String str[]={"Dummy","Dummy","Dummy"};
            spnLocale = (Spinner)findViewById(R.id.spinner1); //1

            ArrayAdapter<String> adapter=new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_item,str);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

            spnLocale.setAdapter(adapter);
spnLocale.setOnItemSelectedListener(new OnItemSelectedListener() {

    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
            long arg3) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub          
    }
});

    }

Answer 3

If you say NullPointerException @ line 2 ie spnLocale.setOnItemSelectedListener(new OnSelectListener()); then spnLocale is null.

You might have referenced the wrong layout. ie the layout you have set to the activity does not have the spinner with the id mentioned.

Edit:

        View rootView = inflater.inflate(R.layout.build,
            container, false);
            spnLocale = (Spinner)rootView.findViewById(R.id.spinner1);
        return rootView;