title: Android sdk: java.lang.NullPointerException: Attempt to invoke virtual method
body: <p>I'm getting this error when I try to debug the app on my device and trying to get rid of it in hours now...and cannot figure it out...Would be awesome if someone could find the solution since I want to release a new update for my app as soon as possible..</p>
  
  <pre><code>07-05 22:45:02.550    2821-2821/davvarn.csgo_maps E/AndroidRuntime﹕ FATAL EXCEPTION: main
      Process: davvarn.csgo_maps, PID: 2821
      java.lang.RuntimeException: Unable to start activity ComponentInfo{davvarn.csgo_maps/davvarn.csgo_maps.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2356)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418)
              at android.app.ActivityThread.access$900(ActivityThread.java:154)
              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
              at android.os.Handler.dispatchMessage(Handler.java:102)
              at android.os.Looper.loop(Looper.java:135)
              at android.app.ActivityThread.main(ActivityThread.java:5289)
              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:904)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
              at davvarn.csgo_maps.MainActivity.changeContent(MainActivity.java:176)
              at davvarn.csgo_maps.MainActivity.onCreate(MainActivity.java:115)
              at android.app.Activity.performCreate(Activity.java:5990)
              at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2309)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418)
              at android.app.ActivityThread.access$900(ActivityThread.java:154)
              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
              at android.os.Handler.dispatchMessage(Handler.java:102)
              at android.os.Looper.loop(Looper.java:135)
              at android.app.ActivityThread.main(ActivityThread.java:5289)
              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:904)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
  </code></pre>
  
  <p>I do not really know how to paste the <code>MainActivity</code> file here, cause I'm new to Stackoverflow. Please let me know how and I will make a try.</p>