title: moveRowAtIndexPath - Moving cells between sections
body: <p>In my UITableView I have this said relationship</p>
  
  <p><code>Department -&lt; Employees</code> (array of names)</p>
  
  <p>I have set up custom objects for each model.</p>
  
  <p>In my <code>moveRowAtIndexPath</code>, I can move in a specific section; however it crashes if I try to move it between sections.</p>
  
  <p>The idea being I want to be able to move "Tom" from "Sales" to "Marketing"</p>
  
  <pre><code>#pragma mark - UITableView delegate
  
  -(NSInteger) numberOfSectionsInTableView:(UITableView *)tableView
  {
      return [_objects count];
  }
  
  -(NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
  {
      Department *department = [_objects objectAtIndex:section];
      return [department.employees count];
  }
  
  - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
  {
      UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"CellId" forIndexPath:indexPath];
  
      // Configure the cell...
      Department *department = [_objects objectAtIndex:indexPath.section];
      Employee *employee = [department.employees objectAtIndex:indexPath.row];
      cell.textLabel.text = employee.name;
  
      return cell;
  }
  
  -(NSString *) tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
  {
      Department *department = [_objects objectAtIndex:section];
      return department.name;
  }
  
  - (BOOL) tableView: (UITableView *) tableView canEditRowAtIndexPath: (NSIndexPath *) indexPath
  {
      return YES;
  }
  
  - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
  {
      if (fromIndexPath == toIndexPath ) return;
  
      Department *department = [_objects objectAtIndex:fromIndexPath.section];
      Employee *employee = [department.employees objectAtIndex:fromIndexPath.row];
  
      [self.tableView beginUpdates];
      [department.employees removeObjectAtIndex:fromIndexPath.row];
      [department.employees insertObject:employee atIndex:toIndexPath.row];
      [self.tableView endUpdates];
  
      [tableView reloadData];
  }
  </code></pre>
  
  <p>How do I get the <code>moveRowAtIndexPath</code> to allow me to move employees from one department to another (or rather one section to another)?</p>
  
  <p>Many thanks</p>
  
  <p>// Crash below;</p>
  
  <pre><code>*** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-2935.137/UITableView.m:1368
  2015-02-20 20:51:15.772 Departments[999:90b] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (3) must be equal to the number of rows contained in that section before the update (2), plus or minus the number of rows inserted or deleted from that section (0 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'
  *** First throw call stack:
  (
      0   CoreFoundation                      0x01a221e4 __exceptionPreprocess + 180
      1   libobjc.A.dylib                     0x017a18e5 objc_exception_throw + 44
      2   CoreFoundation                      0x01a22048 +[NSException raise:format:arguments:] + 136
      3   Foundation                          0x013814de -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 116
      4   UIKit                               0x00539f63 -[UITableView _endCellAnimationsWithContext:] + 13402
      5   UIKit                               0x00549cea -[UITableView endUpdatesWithContext:] + 51
      6   UIKit                               0x00549d18 -[UITableView endUpdates] + 41
      7   Departments                         0x00003a48 -[ViewController tableView:moveRowAtIndexPath:toIndexPath:] + 664
      8   UIKit                               0x005573b4 -[UITableView _endReorderingForCell:wasCancelled:animated:] + 619
      9   UIKit                               0x006e0c4f -[UITableViewCell _grabberReleased:] + 73
      10  UIKit                               0x007d1a1b -[UITableViewCellReorderControl endTrackingWithTouch:withEvent:] + 58
      11  UIKit                               0x005641f1 -[UIControl touchesEnded:withEvent:] + 559
      12  UIKit                               0x004a2ddd -[UIWindow _sendTouchesForEvent:] + 852
      13  UIKit                               0x004a39d1 -[UIWindow sendEvent:] + 1117
      14  UIKit                               0x004755f2 -[UIApplication sendEvent:] + 242
      15  UIKit                               0x0045f353 _UIApplicationHandleEventQueue + 11455
      16  CoreFoundation                      0x019ab77f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
      17  CoreFoundation                      0x019ab10b __CFRunLoopDoSources0 + 235
      18  CoreFoundation                      0x019c81ae __CFRunLoopRun + 910
      19  CoreFoundation                      0x019c79d3 CFRunLoopRunSpecific + 467
      20  CoreFoundation                      0x019c77eb CFRunLoopRunInMode + 123
      21  GraphicsServices                    0x031ee5ee GSEventRunModal + 192
      22  GraphicsServices                    0x031ee42b GSEventRun + 104
      23  UIKit                               0x00461f9b UIApplicationMain + 1225
      24  Departments                         0x000046bd main + 141
      25  libdyld.dylib                       0x02ed5725 start + 0
      26  ???                                 0x00000001 0x0 + 1
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  (lldb) 
  </code></pre>