title: Only the original thread that created a view hierarchy can touch its views
body: <p>I'm trying to get an ImageView to animate between 2 images in my drawable folder.</p>
  
  <p>I thought everything would work fine, but the log is showing an error: <code>Only the original thread that created a view hierarchy can touch its views.</code></p>
  
  <p>Heres my code:</p>
  
  <pre><code>public class ExerciseActivity extends Activity {
      private ExercisesDataSource datasource;
      private Cursor cursor;
      private ImageView image_1_view;
      private Timer _timer;
      private int _index;
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_exercise);     
  
          datasource = new ExercisesDataSource(this);
          datasource.open();
  
          cursor = datasource.fetchExercise(exerciseDataID);
  
          image_1_view = (ImageView) findViewById(R.id.exercise_image);
  
          _index = 1;
          _timer = new Timer();
          _timer.schedule(new TickClass(), 1000);
  
      }
  
      public class TickClass extends TimerTask
      {
          private int columnIndex;
  
          @Override
          public void run() {
              if (_index == 1) {
                  columnIndex = cursor.getColumnIndex(MySQLiteHelper.COLUMN_IMAGE_1);
                  _index = 2;
              }
              else {
                  columnIndex = cursor.getColumnIndex(MySQLiteHelper.COLUMN_IMAGE_2);
                  _index = 1; 
              }   
  
              String image_1 = cursor.getString(columnIndex);
              image_1 = image_1.replace(".png", "");
              int resourceId = getResources().getIdentifier(getPackageName() + ":drawable/" + image_1, null, null);
              image_1_view.setImageDrawable(getResources().getDrawable(resourceId));
          }
      }
  }
  </code></pre>
  
  <p>I went ahead and set the classes and functions to public but that did not fix it.</p>
  
  <p>All of the resources and everything are fine, how do I fix this error?</p>