Spinner and ArrayAdapter NullPointerException in Android

Question

I am not sure why I am getting a NullPointerException, but it is happening at the line spinner.setAdapter(arrayAdapter). Could anyone please have a look at my code to see what the problem is and how to fix it. Thanks in advance.

Here is my code:

public class SlidingTabsActivity extends SherlockFragmentActivity
{

ViewPager viewPager;
TabsAdapter tabsAdapter;
ActionBar actionBarTabs;
Spinner spinner;
ArrayAdapter<String> arrayAdapter;

PopupFirmware popupFirmware; // Popup firmware class instance

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);

    viewPager = new ViewPager(this);
    viewPager.setId(R.id.pager);
    setContentView(viewPager);

    arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, R.array.device_description);
    spinner = (Spinner) findViewById(R.id.tabsSpinner);
    spinner.setAdapter(arrayAdapter);

    actionBarTabs = getSupportActionBar();
    actionBarTabs.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    actionBarTabs.setCustomView(spinner);
    actionBarTabs.setDisplayShowCustomEnabled(true);
    actionBarTabs.setDisplayHomeAsUpEnabled(true);

    tabsAdapter = new TabsAdapter(this, viewPager); // Declares the tabs adapter class with the view pager view

    popupFirmware = new PopupFirmware(this); // Declaring popup firmware class

    /* Adds fragments to the tabs adapter */
    tabsAdapter.addTab(actionBarTabs.newTab().setText("PV"), Fragment_1.class, null);
    tabsAdapter.addTab(actionBarTabs.newTab().setText("CONFIG"), Fragment_2.class, null);
    tabsAdapter.addTab(actionBarTabs.newTab().setText("DIAG"), Fragment_3.class, null);

}

And here is the logcat:

11-20 13:16:26.259: E/AndroidRuntime(11789): FATAL EXCEPTION: main
11-20 13:16:26.259: E/AndroidRuntime(11789): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mobileapplicationretry/com.example.mobileapplicationretry.SlidingTabsActivity}: java.lang.NullPointerException
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.os.Looper.loop(Looper.java:137)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread.main(ActivityThread.java:5103)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at java.lang.reflect.Method.invokeNative(Native Method)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at java.lang.reflect.Method.invoke(Method.java:525)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at dalvik.system.NativeStart.main(Native Method)
11-20 13:16:26.259: E/AndroidRuntime(11789): Caused by: java.lang.NullPointerException
11-20 13:16:26.259: E/AndroidRuntime(11789):    at com.example.mobileapplicationretry.SlidingTabsActivity.onCreate(SlidingTabsActivity.java:51)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.Activity.performCreate(Activity.java:5133)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-20 13:16:26.259: E/AndroidRuntime(11789):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-20 13:16:26.259: E/AndroidRuntime(11789):    ... 11 more

Answer 1

Your spinner is null.
Look, first you create ViewPager and making setContentView:

setContentView(viewPager);

but your ViewPager is empty cause you haven't put anything to it. And next you call:

spinner = (Spinner) findViewById(R.id.tabsSpinner);

it means that findViewById will look for your spinner starting root view of your Activity - ViewPager you've create earlier, which is empty. So Spinner never will be found - and it is always null.