title: Unable to start activity ComponentInfo{..} : java.lang.NullPointerException
body: <p>I'm trying to start a new activity when the Button playlistBtn is clicked, and I'm getting a NullPointerException, but I can't see where did I go wrong with my references.</p>
  
  <p>Complete error log:</p>
  
  <pre><code>04-08 17:02:07.847: E/AndroidRuntime(5869): FATAL EXCEPTION: main
  04-08 17:02:07.847: E/AndroidRuntime(5869): java.lang.RuntimeException: Unable to start activity ComponentInfo{app.and.androidmusic/app.and.androidmusic.PlaylistActivity}: java.lang.NullPointerException
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.os.Handler.dispatchMessage(Handler.java:99)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.os.Looper.loop(Looper.java:137)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread.main(ActivityThread.java:5039)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at java.lang.reflect.Method.invokeNative(Native Method)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at java.lang.reflect.Method.invoke(Method.java:511)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at dalvik.system.NativeStart.main(Native Method)
  04-08 17:02:07.847: E/AndroidRuntime(5869): Caused by: java.lang.NullPointerException
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at app.and.androidmusic.PlaylistActivity.onCreate(PlaylistActivity.java:68)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.Activity.performCreate(Activity.java:5104)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
  04-08 17:02:07.847: E/AndroidRuntime(5869):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)   
  </code></pre>
  
  <p>MainActivity.java:</p>
  
  <pre><code>    public class MainActivity extends ListActivity {
  ...
  protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  ...
  Button btnPlaylist = (Button) findViewById(R.id.playlistBtn);
  btnPlaylist.setOnClickListener(new View.OnClickListener() {                 
                       @Override
              public void onClick(View arg0) {
              Intent in = new Intent(getApplicationContext(), PlaylistActivity.class);
                          startActivity(in);
  </code></pre>
  
  <p>PlaylistActivity.java:</p>
  
  <pre><code>public class PlaylistActivity extends ListActivity{
  ...
  @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_playlist); {
  </code></pre>
  
  <p>AndroidManifest.xml:</p>
  
  <pre><code>&lt;activity
              android:name="app.and.androidmusic.MainActivity"
              android:label="@string/app_name" &gt;
              &lt;intent-filter&gt;
                  &lt;action android:name="android.intent.action.MAIN" /&gt;
                  &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
              &lt;/intent-filter&gt;
          &lt;/activity&gt;        
          &lt;activity
              android:name=".PlaylistActivity" /&gt;
  </code></pre>
  
  <p>Ok, so here is activity_main.xml as you asked it's quite long:</p>
  
  <pre><code>&lt;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"
      tools:context=".MainActivity" &gt;
  
      &lt;app.and.androidmusic.DragNDropListView
          android:id="@+id/android:list"
          android:layout_width="match_parent"
          android:layout_height="300dp"
          android:layout_below="@+id/playlistBtn"
          android:layout_alignParentLeft="true" &gt;
  
    &lt;/app.and.androidmusic.DragNDropListView&gt;
  
      &lt;Button
          android:id="@+id/playBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
         android:layout_below="@id/android:list"
          android:layout_toRightOf="@+id/prevBtn"
          android:text="@string/playBtn" /&gt;
  
      &lt;Button
          android:id="@+id/pauseBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@id/android:list"
          android:layout_toRightOf="@+id/playBtn"
          android:text="@string/pauseBtn" /&gt;
  
      &lt;Button
          android:id="@+id/prevBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@id/android:list"
          android:text="@string/prevBtn" /&gt;
  
      &lt;Button
          android:id="@+id/nextBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@id/android:list"
          android:layout_toRightOf="@+id/pauseBtn"
          android:text="@string/nextBtn" /&gt;
  
       &lt;Button
          android:id="@+id/songsBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@+id/songTxt"
          android:text="@string/songsBtn" /&gt;
  
       &lt;Button
          android:id="@+id/playlistBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@+id/songTxt"
          android:layout_toRightOf="@+id/songsBtn"
          android:text="@string/playlistBtn" /&gt;
  
       &lt;Button
          android:id="@+id/eqBtn"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_below="@+id/songTxt"
          android:layout_toRightOf="@+id/playlistBtn"
          android:text="@string/eqBtn" /&gt;
  
       &lt;TextView
           android:id="@+id/songTxt"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_alignParentTop="true"
           android:layout_centerHorizontal="true"
           android:text="" /&gt;
  
  &lt;/RelativeLayout&gt;
  </code></pre>