VB.Net Picturebox“参数无效”获取在线图像时答案

【问题标题】：VB.Net Picturebox "Parameter is not Valid" when get online imagesVB.Net Picturebox“参数无效”获取在线图像时
【发布时间】：2014-08-07 22:00:57
【问题描述】：

Dim ShowImgWebClient = New WebClient
Dim ImageInBytes As Byte() = ShowImgWebClient.DownloadData("http://ex.domain.com/index.php?checksum=" & lblCheckSum.Text.ToString())
Dim ImageStream As New MemoryStream(ImageInBytes)
Dim CaptchaImg As Image = New Bitmap(ImageStream)
ptbCaptcha.Image = CaptchaImg

我正在使用此代码为我的图片框名称获取在线验证码ptbCaptcha。

但是当我请求这个图像时，我的程序显示错误参数无效。

为什么会这样？以及如何让它发挥作用？

【问题讨论】：

可能是这样的：lblCheckSum.Text。删除.ToString()。它已经是一个字符串..
错误是由这个引起的吗？
将 ImageStream 调暗为新的 MemoryStream(ImageInBytes)
错误发生在哪一行？确切的消息是什么（包括堆栈跟踪，如果可能的话）？

标签： vb.net picturebox

【解决方案1】：

这不是使用MemoryStream 的正确方法。

以下是来自微软网站的示例：

Imports System
Imports System.IO
Imports System.Text

Module MemStream

    Sub Main()

        Dim count As Integer 
        Dim byteArray As Byte()
        Dim charArray As Char()
        Dim uniEncoding As New UnicodeEncoding()

        ' Create the data to write to the stream. 
        Dim firstString As Byte() = _
            uniEncoding.GetBytes("Invalid file path characters are: ")
        Dim secondString As Byte() = _
            uniEncoding.GetBytes(Path.GetInvalidPathChars())

        Dim memStream As New MemoryStream(100)
        Try 
            ' Write the first string to the stream.
            memStream.Write(firstString, 0 , firstString.Length)

            ' Write the second string to the stream, byte by byte.
            count = 0
            While(count < secondString.Length)
                memStream.WriteByte(secondString(count))
                count += 1
            End While 

            ' Write the stream properties to the console.
            Console.WriteLine( _
                "Capacity = {0}, Length = {1}, Position = {2}", _
                memStream.Capacity.ToString(), _
                memStream.Length.ToString(), _
                memStream.Position.ToString())

            ' Set the stream position to the beginning of the stream.
            memStream.Seek(0, SeekOrigin.Begin)

            ' Read the first 20 bytes from the stream.
            byteArray = _
                New Byte(CType(memStream.Length, Integer)){}
            count = memStream.Read(byteArray, 0, 20)

            ' Read the remaining Bytes, Byte by Byte. 
            While(count < memStream.Length)
                byteArray(count) = _
                    Convert.ToByte(memStream.ReadByte())
                count += 1
            End While 

            ' Decode the Byte array into a Char array  
            ' and write it to the console.
            charArray = _
                New Char(uniEncoding.GetCharCount( _
                byteArray, 0, count)){}
            uniEncoding.GetDecoder().GetChars( _
                byteArray, 0, count, charArray, 0)
            Console.WriteLine(charArray)
        Finally
            memStream.Close()
        End Try 

    End Sub 
End Module

更多信息请参见MemoryStream。

【讨论】：