vb.net - 上传多个文件 (VB.Net)

Question

我尝试使用 VB.Net 代码上传多个文件，但没有成功。当有多个文件时，我最终在网络服务器上只有一个文件(对于多个元素，FileExists 为 True)。如果我在其他某个地方完成循环，则会引发异常。

这是我的代码:

Imports System.Net
Imports System.IO

Sub upload()
    Dim filepath As String = IO.Path.Combine(Application.StartupPath, "C:\i.bmp")
    Dim filepath2 As String = IO.Path.Combine(Application.StartupPath, "C:\i.txt")
    Dim url As String = "http://localhost/SEND/MultUp.php"

    Dim Element As Object
    Dim sNames(0 To 3) As String 'Array declaration

    sNames(0) = filepath2
    sNames(1) = ""
    sNames(2) = ""
    sNames(3) = filepath

    Dim boundary As String = IO.Path.GetRandomFileName
    Dim header As New System.Text.StringBuilder()

    For Each Element In sNames 'Roaming all elements of array
        If File.Exists(Element) Then
            header.AppendLine("--" & boundary)
            header.Append("Content-Disposition: form-data; name=""files[]"";")
            header.AppendFormat("filename=""{0}""", IO.Path.GetFileName(Element))
            header.AppendLine()
            header.AppendLine("Content-Type: application/octet-stream")
            header.AppendLine()

            Dim headerbytes() As Byte = System.Text.Encoding.UTF8.GetBytes(header.ToString)
            Dim endboundarybytes() As Byte = System.Text.Encoding.ASCII.GetBytes(vbNewLine & "--" & boundary & "--" & vbNewLine)

            Dim req As Net.HttpWebRequest = Net.HttpWebRequest.Create(url)
            req.ContentType = "multipart/form-data; boundary=" & boundary
            req.ContentLength = headerbytes.Length + New IO.FileInfo(Element).Length + endboundarybytes.Length
            req.Method = "POST"

            Dim s As IO.Stream = req.GetRequestStream
            s.Write(headerbytes, 0, headerbytes.Length)
            Dim filebytes() As Byte = My.Computer.FileSystem.ReadAllBytes(Element)
            s.Write(filebytes, 0, filebytes.Length)
            s.Write(endboundarybytes, 0, endboundarybytes.Length)
            s.Close()

            header.clear() 'this was missing in my original source code
        End If
    Next
End Sub

Answer 1

完全归功于jmcilhinney's comment :

最初发布的代码缺少 header.clear() 调用。因此，当处理多个元素时，header 变量继续追加行。

更好的做法是在 For Each 循环中声明 header StringBuilder 变量。它使得它easier to maintain ，编译器应该以任何一种方式优化它。由于 header 不在循环之外使用，因此应该在最窄的范围内使用它。