显示图像

Question

我的老师给了我们示例代码，它非常类似于下面的代码。我还没有收到他的回信，想知道为什么我的代码无法正常工作。有人能给我一些建议，说明我做错了什么，或者更简单的方法来显示图像。谢谢你的时间。

<%@ WebHandler Language="VB" Class="images" %> 

Imports System 
Imports System.Web 
Imports System.Data.SqlClient 
Public Class images : Implements IHttpHandler 

    Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest 


     Dim id As String = context.Request.QueryString("ImageId") 
     Dim userId As Integer = 4 


     Dim conn As New System.Data.SqlClient.SqlConnection 


     Dim cmd As New System.Data.SqlClient.SqlCommand 


     conn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString 
     cmd.Connection = conn 
     cmd.CommandText = "SELECT Image FROM mrg_Image WHERE UserId=@userId" 
     cmd.Parameters.AddWithValue("@userId", userId) 

     conn.Open() 
     Dim file_bytes As Byte() = cmd.ExecuteScalar()   
     Dim file_bytes_stream As New System.IO.MemoryStream(file_bytes) 

     'During the build - The next line of code is highlighted green with the error message of, "Parameter is invalid" 

     Dim the_image As New System.Drawing.Bitmap(file_bytes_stream) 

     context.Response.ContentType = "image/jpg" 
     the_image.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)   

     conn.Close() 
    End Sub 

    Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable 
     Get 
      Return False 
     End Get 
    End Property 

End Class 

Answer 1

编辑：在评论中回答（如是）。提问者的代码很好...

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看起来不错。你是否在下面的第一行和最后一行之间进行了implict类型转换？

Dim file_bytes_stream As New System.IO.MemoryStream(file_bytes) 

'During the build - The next line of code is highlighted green with the error message of, "Parameter is invalid" 

Dim the_image As New System.Drawing.Bitmap(file_bytes_stream) 

如果你有option explicit集，你可能需要做...

Dim file_bytes_memory_stream As New System.IO.MemoryStream(file_bytes) 

Dim file_bytes_stream as System.IO.Stream = DirectCast(file_bytes_memory_stream, System.IO.Stream) 

Dim the_image As New System.Drawing.Bitmap(file_bytes_stream)