title: How to go back to RootViewController from presentView controller?
body: <p>I am developing a iPhone Photos Gallery app and In my app I created one folder into gallery and that gallery folder is shown up into my app and while use click on Image its navigate to the next view controller where he can see a full size image and I set trash button there so user can delete that photos and my trashButton code is :</p>
  
  <pre><code>@IBAction func btnTrash(sender: AnyObject) {
  
      let alert = UIAlertController(title: "Delete Image", message: "Are You Sure To delete this Image?", preferredStyle: .Alert)
      alert.addAction(UIAlertAction(title: "Yes", style: .Default, handler: {(alertAction)in
          //Delete Photo
  
          PHPhotoLibrary.sharedPhotoLibrary().performChanges({
              let request = PHAssetCollectionChangeRequest(forAssetCollection: self.assetCollection)
              request.removeAssets([self.photosAsset[self.index]])
              }, completionHandler: {(success, error )in
                  NSLog("\nDeleted Image -&gt; %@", (success ? "Success" : "Error"))
                  alert.dismissViewControllerAnimated(true, completion: nil)
  
                  self.photosAsset = PHAsset.fetchAssetsInAssetCollection(self.assetCollection, options: nil)
                  if(self.photosAsset.count == 0){
  
                      // No photos Left
                      self.imgView.image = nil
                      println("No Image Left")
  
                      // Pop to root view controller
                      self.navigationController?.popToRootViewControllerAnimated(true)
  
                  }
                  if(self.index &gt;= self.photosAsset.count){
                      self.index = self.photosAsset.count - 1
                  }
                  self.displayPhoto()
          })
  
      }))
      alert.addAction(UIAlertAction(title: "Cancle", style: .Cancel, handler: {(alertAction)in
      //Do not delete Photo
  
      self.dismissViewControllerAnimated(true, completion: nil)
      }))
      self.presentViewController(alert, animated: true, completion: nil)
  }
  </code></pre>
  
  <p>I have set if there is not image left than use will navigate to the <code>RootViewController</code> with this line of code:</p>
  
  <pre><code> self.navigationController?.popToRootViewControllerAnimated(true)
  </code></pre>
  
  <p>But this is not working and when the last image is deleted I got a window:</p>
  
  <p><img src="https://i.stack.imgur.com/EXzrc.png" alt="enter image description here"></p>
  
  <p>and my console shows up:</p>
  
  <pre><code>2014-11-05 16:45:11.502 Photos Gallary App[3046:115145] Adding Image to Library -&gt; Success
  2014-11-05 16:45:15.285 Photos Gallary App[3046:115146] 
  Deleted Image -&gt; Success
  No Image Left
  2014-11-05 16:45:15.287 Photos Gallary App[3046:115146] *** Terminating app due to uncaught exception 'NSRangeException', reason: '0x7f95fb5ef980: index (18446744073709551615) beyond bounds (0)'
  *** First throw call stack:
  (
      0   CoreFoundation                      0x0000000100e4f3f5 __exceptionPreprocess + 165
      1   libobjc.A.dylib                     0x000000010297dbb7 objc_exception_throw + 45
      2   CoreFoundation                      0x0000000100e4f32d +[NSException raise:format:] + 205
      3   Photos                              0x0000000100c5dd27 -[PHBatchFetchingArray objectAtIndex:] + 105
      4   Photos                              0x0000000100c63b92 -[PHFetchResult objectAtIndexedSubscript:] + 57
      5   Photos Gallary App                  0x0000000100b4d8d6 _TFC18Photos_Gallary_App9ViewPhoto12displayPhotofS0_FT_T_ + 694
      6   Photos Gallary App                  0x0000000100b50d93 _TFFFC18Photos_Gallary_App9ViewPhoto8btnTrashFS0_FPSs9AnyObject_T_U_FGSQCSo13UIAlertAction_T_U0_FTSbGSQCSo7NSError__T_ + 4243
      7   Photos Gallary App                  0x0000000100b4a6f6 _TTRXFo_dSboGSQCSo7NSError__dT__XFo_iTSbGSQS____iT__ + 38
      8   Photos Gallary App                  0x0000000100b4ed91 _TPA__TTRXFo_dSboGSQCSo7NSError__dT__XFo_iTSbGSQS____iT__ + 81
      9   Photos Gallary App                  0x0000000100b4a728 _TTRXFo_iTSbGSQCSo7NSError___iT__XFo_dSboGSQS___dT__ + 40
      10  Photos Gallary App                  0x0000000100b4a788 _TTRXFo_dSboGSQCSo7NSError__dT__XFdCb_dV10ObjectiveC8ObjCBooldGSQS___dT__ + 88
      11  libdispatch.dylib                   0x000000010541ccc6 _dispatch_call_block_and_release + 12
      12  libdispatch.dylib                   0x000000010543a7f4 _dispatch_client_callout + 8
      13  libdispatch.dylib                   0x0000000105425193 _dispatch_root_queue_drain + 1094
      14  libdispatch.dylib                   0x000000010542663c _dispatch_worker_thread2 + 52
      15  libsystem_pthread.dylib             0x00000001057d0ef8 _pthread_wqthread + 314
      16  libsystem_pthread.dylib             0x00000001057d3fb9 start_wqthread + 13
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  (lldb) 
  </code></pre>
  
  <p>Can anybody tell me what is happening and what is the solution for this?</p>