nodesForXPath returning 0 objects

Question

I have problems parsing elements from a XML String to an Array with TouchXML.

I've succesfully made an CXMLDocument object with:

 CXMLDocument *doc = 
[[CXMLDocument alloc] initWithXMLString:responseString options:0 error:&error];

I'm now trying to get all elements under "Vehicles" with:

NSArray *items = [[doc rootElement] nodesForXPath:@"//Vehicles" error:&error];

This returns 0 objects for the array. What am I doing wrong?

The CXMLDocument output:

<CXMLDocument 0x21043480 [0x24a64650]> <?xml version="1.0" encoding="utf-8"?>
<System xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://howdoi.org/">
  <Vehicles>
    <VehicleUnit>
      <Plate>2353        </Plate>
      <LastGPStime>2013-07-06 13:02</LastGPStime>
      <LastLatitude>60.35405</LastLatitude>
      <LastLongitude>5.36675</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>177</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2355        </Plate>
      <LastGPStime>2013-07-06 13:02</LastGPStime>
      <LastLatitude>60.35571</LastLatitude>
      <LastLongitude>5.36802</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>84.9</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2356        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.2893</LastLatitude>
      <LastLongitude>5.22843</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>224.4</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2357        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.39097</LastLatitude>
      <LastLongitude>5.32535</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>27.4</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2358        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.39585</LastLatitude>
      <LastLongitude>5.3254</LastLongitude>
      <LastSpeed>16.56</LastSpeed>
      <LastCourse>141.5</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2359        </Plate>
      <LastGPStime>2013-07-06 13:02</LastGPStime>
      <LastLatitude>60.39801</LastLatitude>
      <LastLongitude>5.32231</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>12.8</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2360        </Plate>
      <LastGPStime>2013-07-06 13:02</LastGPStime>
      <LastLatitude>60.35562</LastLatitude>
      <LastLongitude>5.36813</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>65.8</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2361        </Plate>
      <LastGPStime>2013-07-06 13:02</LastGPStime>
      <LastLatitude>60.39897</LastLatitude>
      <LastLongitude>5.32094</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>9.5</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2362        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.28878</LastLatitude>
      <LastLongitude>5.22882</LastLongitude>
      <LastSpeed>22.68</LastSpeed>
      <LastCourse>106.6</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2363        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.34393</LastLatitude>
      <LastLongitude>5.33881</LastLongitude>
      <LastSpeed>78.84</LastSpeed>
      <LastCourse>169.4</LastCourse>
    </VehicleUnit>
    <VehicleUnit>
      <Plate>2364        </Plate>
      <LastGPStime>2013-07-06 13:03</LastGPStime>
      <LastLatitude>60.28939</LastLatitude>
      <LastLongitude>5.2284</LastLongitude>
      <LastSpeed>0</LastSpeed>
      <LastCourse>234.3</LastCourse>
    </VehicleUnit>
  </Vehicles>
</System>

Answer 1

I got it working, had to use namespaceMappings as following:

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
                              @"http://howdoi.org/",
                              @"howdoi",
                              nil];
NSArray *items = [doc nodesForXPath:@"//howdoi:VehicleUnit" namespaceMappings:dict error:nil];

This sets the array to 11 items and let me do what i want :)