title: Setting programmatically the layout background color = nullpointerexc
body: <p>I'm using shared preferences in my app to set different background colors.</p>
  
  <pre><code>private void loadPreferences(){
      SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
  
      boolean isBackgroundDark = sharedPreferences.getBoolean("background_color",false);
      if(isBackgroundDark){
          LinearLayout mainLayout = (LinearLayout) findViewById(R.id.mainActivityLayout);
          mainLayout.setBackgroundColor(Color.parseColor("#3c3f41"));
  
      }
      String notebookTitle = sharedPreferences.getString("title","Notebook");
      setTitle(notebookTitle);
  }
  </code></pre>
  
  <p>This code works fine, the color of mainlayout changes.
  But when I want change the color of simply row item</p>
  
  <p>private void loadPreferences(){
          SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);</p>
  
  <pre><code>    boolean isBackgroundDark = sharedPreferences.getBoolean("background_color",false);
      if(isBackgroundDark){
          LinearLayout mainLayout = (LinearLayout) findViewById(R.id.mainActivityLayout);
          mainLayout.setBackgroundColor(Color.parseColor("#3c3f41"));
          RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.list_row_rel_layout);
          relativeLayout.setBackgroundColor(Color.parseColor("#3c3f41"));
      }
      String notebookTitle = sharedPreferences.getString("title","Notebook");
      setTitle(notebookTitle);
  }
  </code></pre>
  
  <p>In the xml file of this relative layout the id is define</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#FFF9F9F9"
        android:id="@+id/list_row_rel_layout"
        android:paddingRight="10dp"
        android:paddingTop="10dp"
        android:paddingBottom="10dp"...
  /&gt;
  </code></pre>
  
  <p>Logs below:</p>
  
  <pre><code>FATAL EXCEPTION: main
                                                                       Process: com.bczyzowski.notebook, PID: 20754
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bczyzowski.notebook/com.bczyzowski.notebook.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setBackgroundColor(int)' on a null object reference
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setBackgroundColor(int)' on a null object reference
                                                                           at com.bczyzowski.notebook.MainActivity.loadPreferences(MainActivity.java:77)
                                                                           at com.bczyzowski.notebook.MainActivity.onCreate(MainActivity.java:34)
                                                                           at android.app.Activity.performCreate(Activity.java:6237)
                                                                           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                           at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                           at android.os.Looper.loop(Looper.java:148) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                           at java.lang.reflect.Method.invoke(Native Method) 
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
  </code></pre>