用了ioutil.ReadFile()来读取文件，就不必用os.Open()了，所以正确的写法是：

package main
import (
    "bytes"
    "encoding/xml"
    "fmt"
    "io/ioutil"
)

func main() {
    //    file, err := os.Open(xmlFile)
    //    if err != nil {
    //        panic(err)
    //    }

    data, err := ioutil.ReadFile("vsproj.csproj")
    if err != nil {
        panic(err)
    }

    //defer file.Close()
    NodeDecoder := xml.NewDecoder(bytes.NewBuffer(data))

    var t xml.Token

    for t, err = NodeDecoder.Token(); err == nil; t, err = NodeDecoder.Token() {
        switch token := t.(type) {
        case xml.StartElement:
            name := token.Name.Local
            fmt.Println(name)

        case xml.EndElement:
        }

    }
}