xml.unmarshal不遍历XML树

Question

I am attempting to marshal XML over to a set of custom structs and it isn't working as I would expect. I would expect that the xml.StartElement for each of my "UnmarshalXML" functions would change for each object that it is processing (e.g. TrainingCenterDatabase vs Activities). That doesn't appear to be happening. My xml.StartElement is always the root element of the entire XML File.

In addition, my final decoded Struct is empty when the Unmarshaling is completed. I hypothesize that because the wrong "startElement" is being passed in then it isn't finding any values to parse.

What am I doing wrong?

Structs and Functions:

func (v *TrainingCenterDatabase) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
    decodeError := d.DecodeElement(&v.Activities, &startElement)
    fmt.Println("TrainingCenterDatabase StartELement Name: " + startElement.Name.Local)
    if decodeError != nil {
        logging.LogError("tcxhelper - XMLTpxFile.UnmarshalXML Error - "+decodeError.Error(), "")
        return decodeError
    }
    return nil
}

func (v *Activities) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
    decodeError := d.DecodeElement(&v.Activity, &startElement)
    fmt.Println("Activities StartELement Name: " + startElement.Name.Local)
    if decodeError != nil {
        logging.LogError("tcxhelper - XMLTpxFile.UnmarshalXML Error - "+decodeError.Error(), "")
        return decodeError
    }
    return nil
}

func (v *Activity) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
    for _, attr := range startElement.Attr {
        fmt.Println("Attr Name: " + attr.Name.Local)
        fmt.Println("Attr Value: " + attr.Value)
    }
    fmt.Println("Activity StartELement Name: " + startElement.Name.Local)

    decodeError := d.DecodeElement(&v.Lap, &startElement)
    if decodeError != nil {
        logging.LogError("tcxhelper - XMLTpxFile.UnmarshalXML Error - "+decodeError.Error(), "")
        return decodeError
    }
    return nil
}

type TpxFile struct {
    TpxFile TrainingCenterDatabase `xml:"TrainingCenterDatabase"`
}

type TrainingCenterDatabase struct {
    Activities Activities `xml:"Activities"`
}

type Activities struct {
    Activity Activity `xml:"Activity"`
}

type Activity struct {
    Sport string    `xml:"Sport"`
    ID    time.Time `xml:"Id"`
    Lap   Lap       `xml:"Lap"`
}

type Lap struct {
    Cadence       string `xml:"Cadence"`
    TriggerMethod string `xml:"TriggerMethod"`
    Track         Track  `xml:"Track"`
}

type Track struct {
    Trackpoint          Trackpoint          `xml:"Trackpoint"`
    MaximumSpeed        string              `xml:"MaximumSpeed"`
    MaximumHeartRateBpm MaximumHeartRateBpm `xml:"MaximumHeartRateBpm"`
    Intensity           string              `xml:"Intensity"`
    Calories            string              `xml:"Calories"`
    AverageHeartRateBpm AverageHeartRateBpm `xml:"AverageHeartRateBpm"`
    StartTime           time.Time           `xml:"StartTime"`
    TotalTimeSeconds    string              `xml:"TotalTimeSeconds"`
    DistanceMeters      string              `xml:"DistanceMeters"`
}

type MaximumHeartRateBpm struct {
    Value string `xml:"Value"`
}

type AverageHeartRateBpm struct {
    Value string `xml:"Value"`
}

type Trackpoint []struct {
    Position       Position     `xml:"Position"`
    AltitudeMeters string       `xml:"AltitudeMeters"`
    DistanceMeters string       `xml:"DistanceMeters"`
    HeartRateBpm   HeartRateBpm `xml:"HeartRateBpm"`
    Cadence        string       `xml:"Cadence"`
    Extensions     Extensions   `xml:"Extensions"`
    Time           time.Time    `xml:"Time"`
}

type Extensions struct {
    TPX TPX `xml:"TPX"`
}

type TPX struct {
    Xmlns string `xml:"xmlns"`
    Speed string `xml:"Speed"`
    Watts string `xml:"Watts"`
}
type HeartRateBpm struct {
    Value string `xml:"Value"`
}

type Position struct {
    LatitudeDegrees  string `xml:"LatitudeDegrees"`
    LongitudeDegrees string `xml:"LongitudeDegrees"`
} 

Code to Marshal

func TestMarshalTPX(t *testing.T) {

    fileByteArray, myErr := ioutil.ReadFile("/my/local/directory/Lunch_Ride.tcx")
    if myErr != nil {
        t.Error("Error Reading File: " + myErr.Error())
    }
    tpxFile := TrainingCenterDatabase{}

    marshalError := xml.Unmarshal(fileByteArray, &tpxFile)
    if marshalError != nil {
        t.Error("Marshal Error: " + marshalError.Error())
    }
}

Sample XML:

<?xml version="1.0" encoding="UTF-8"?>
<TrainingCenterDatabase
  xsi:schemaLocation="http://www.garmin.com/xmlschemas/TrainingCenterDatabase/v2 http://www.garmin.com/xmlschemas/TrainingCenterDatabasev2.xsd"
  xmlns:ns5="http://www.garmin.com/xmlschemas/ActivityGoals/v1"
  xmlns:ns3="http://www.garmin.com/xmlschemas/ActivityExtension/v2"
  xmlns:ns2="http://www.garmin.com/xmlschemas/UserProfile/v2"
  xmlns="http://www.garmin.com/xmlschemas/TrainingCenterDatabase/v2"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <Activities>
  <Activity Sport="Biking">
   <Id>2018-10-16T18:41:12Z</Id>
   <Lap StartTime="2018-10-16T18:41:12Z">
    <TotalTimeSeconds>3732</TotalTimeSeconds>
    <DistanceMeters>26451.5</DistanceMeters>
    <MaximumSpeed>52560.0</MaximumSpeed>
    <Calories>0</Calories>
    <AverageHeartRateBpm>
     <Value>148</Value>
    </AverageHeartRateBpm>
    <MaximumHeartRateBpm>
     <Value>188</Value>
    </MaximumHeartRateBpm>
    <Intensity>Active</Intensity>
    <Cadence>79</Cadence>
    <TriggerMethod>Manual</TriggerMethod>
    <Track>
     <Trackpoint>
      <Time>2018-10-16T18:41:12Z</Time>
      <Position>
       <LatitudeDegrees>39.7711140</LatitudeDegrees>
       <LongitudeDegrees>-105.0392580</LongitudeDegrees>
      </Position>
      <AltitudeMeters>1646.2</AltitudeMeters>
      <DistanceMeters>0.0</DistanceMeters>
      <HeartRateBpm>
       <Value>97</Value>
      </HeartRateBpm>
      <Cadence>69</Cadence>
      <Extensions>
       <TPX xmlns="http://www.garmin.com/xmlschemas/ActivityExtension/v2">
        <Speed>0.0</Speed>
        <Watts>320</Watts>
       </TPX>
      </Extensions>
     </Trackpoint>
     <Trackpoint>
      <Time>2018-10-16T18:41:13Z</Time>
      <Position>
       <LatitudeDegrees>39.7711120</LatitudeDegrees>
       <LongitudeDegrees>-105.0392590</LongitudeDegrees>
      </Position>
      <AltitudeMeters>1646.2</AltitudeMeters>
      <DistanceMeters>0.2</DistanceMeters>
      <HeartRateBpm>
       <Value>97</Value>
      </HeartRateBpm>
      <Cadence>73</Cadence>
      <Extensions>
       <TPX xmlns="http://www.garmin.com/xmlschemas/ActivityExtension/v2">
        <Speed>0.2</Speed>
        <Watts>195</Watts>
       </TPX>
      </Extensions>
     </Trackpoint>
    </Track>
   </Lap>
  </Activity>
 </Activities>
</TrainingCenterDatabase>