title: Spinner Error when set setOnItemSelectedListener
body: <p>When i used spinner for dropdown list or <code>setOnItemSelectedListener</code> error occurs:</p>
  
  <p>nav_login.xml:</p>
  
  <pre><code>&lt;Spinner
      android:layout_width="20dp"
      android:layout_height="12dp"
      android:id="@+id/spinner"
      android:layout_alignParentBottom="true"
      android:layout_alignParentRight="true"
      android:layout_alignParentEnd="true"
      android:layout_alignParentLeft="false"
      android:layout_alignParentTop="false"
      android:layout_alignWithParentIfMissing="false"
      android:layout_marginRight="30dp"
      android:layout_marginBottom="12dp"
      android:entries="@array/items" /&gt;
  </code></pre>
  
  <p>strinarray:</p>
  
  <pre><code>&lt;string-array name="items"&gt;
      &lt;item&gt;Log Out&lt;/item&gt;
      &lt;item&gt;Setting&lt;/item&gt;
  &lt;/string-array&gt;
  </code></pre>
  
  <p>MainActivity:</p>
  
  <pre><code>  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
  
      Firebase.setAndroidContext(this);
      Firebase rootRef = new Firebase("https://intense-heat-4844.firebaseio.com/property");
  
      navigationView = (NavigationView) findViewById(R.id.nav_view);
      View mLoginButton = navigationView.inflateHeaderView(R.layout.nav_header);
      mLoginButton.findViewById(R.id.Login);
      if (!myBooleanVariable) {
          mLoginButton.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  //Calling activity LoginRegister
                  Intent intent = new Intent(getApplication(), LoginRegister.class);
                  startActivity(intent);
              }
          });
      }
  
      Intent intent = getIntent();
      if (null != intent) {
          myBooleanVariable = intent.getBooleanExtra("my_boolean_key", myBooleanVariable);
          if (myBooleanVariable) {
              navigationView.getHeaderView(0).setVisibility(View.GONE);
              navigationView = (NavigationView) findViewById(R.id.nav_view);
              View mUserLoggedIn = navigationView.inflateHeaderView(R.layout.nav_header_login);
  
  
              final Spinner spinner;
              spinner = (Spinner) findViewById(R.id.spinner);
              spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                  @Override
                  public void onItemSelected(AdapterView&lt;?&gt; arg0, View arg1,
                                             int arg2, long arg3) {
                      String msupplier = spinner.getSelectedItem().toString();
  
                      Log.e("Selected item : ", msupplier);
  
                      Intent intent = new Intent(getApplication(), Spinner.class);
                      startActivity(intent);
                  }
  
                  @Override
                  public void onNothingSelected(AdapterView&lt;?&gt; arg0) {
  
                  }
              });
  
  
  
          }
      }
  
      ePager = (ViewPager) findViewById(R.id.Pager);
      ePager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
      eTabs = (SlidingTabLayout) findViewById(R.id.TabLayout);
      eTabs.setViewPager(ePager);
  
      Toolbartext = (TextView) findViewById(R.id.toolbar_title);
      toolbar = (Toolbar) findViewById(R.id.app_bar);
      setSupportActionBar(toolbar);
      Toolbartext.setText("Residential Search");
  
      getSupportActionBar().setDisplayShowHomeEnabled(true);
      Navigation1 drawerfragment = (Navigation1)
              getSupportFragmentManager().findFragmentById(R.id.fragment_navigation1);
      drawerfragment.setup(R.id.fragment_navigation1, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar);
  
  
  }
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.menu_main, menu);
      return true;
  }
  
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.
      int id = item.getItemId();
  
      //noinspection SimplifiableIfStatement
      if (id == R.id.action_settings) {
          Toast.makeText(this, "hitted item" + item.getTitle(), Toast.LENGTH_SHORT).show();
          return true;
      }
  
      return super.onOptionsItemSelected(item);
  }
  </code></pre>
  
  <p>Exception:</p>
  
  <pre><code>03-01 13:17:47.039    8587-8587/com.example.syedsaadali.myapplication I/System.out﹕ User ID: 4310e794-0b9b-4fad-afd0-e3f73c5f7412, Provider: password
  03-01 13:17:47.074    8587-8587/com.example.syedsaadali.myapplication D/AndroidRuntime﹕ Shutting down VM
  03-01 13:17:47.074    8587-8587/com.example.syedsaadali.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
      Process: com.example.syedsaadali.myapplication, PID: 8587
      java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.syedsaadali.myapplication/com.example.syedsaadali.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setOnItemSelectedListener(android.widget.AdapterView$OnItemSelectedListener)' on a null object reference
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
              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:5254)
              at java.lang.reflect.Method.invoke(Native Method)
              at java.lang.reflect.Method.invoke(Method.java:372)
              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setOnItemSelectedListener(android.widget.AdapterView$OnItemSelectedListener)' on a null object reference
              at com.example.syedsaadali.myapplication.MainActivity.onCreate(MainActivity.java:72)
  </code></pre>