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Rendering Images in ASP.NET Directly from Your Database, Page 2

  • August 1, 2007
  • By Paul Kimmel, Paul Kimmel
  • Send Email »
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Listing 2: The abridged ProductPhoto class (that contains enough information for demonstration purposes).

Imports Microsoft.VisualBasic
Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.IO


Public Class ProductPhoto

   Public Sub New(ByVal ProductPhotoID As Integer, _
                  ByVal LargePhoto As Byte())
      Me.FProductPhotoID = ProductPhotoID
      SetLargePhoto(LargePhoto)
   End Sub

   Private Sub SetLargePhoto(ByVal photo As Byte())
      Dim stream As MemoryStream = New MemoryStream(photo)
      LargePhoto = Image.FromStream(stream)
   End Sub

   Private FProductPhotoID As Integer
   Public ReadOnly Property ProductPhotoID() As Integer
      Get
         Return FProductPhotoID
      End Get
   End Property

   Private FLargePhoto As Image
   Public Property LargePhoto() As Image
      Get
         Return FLargePhoto
      End Get
      Set(ByVal value As Image)
         FLargePhoto = value
      End Set
   End Property

End Class

The key to getting the SQL Server Image type into a System.Drawing.Image type is to load a stream and construct the image from the stream, as shown in SetLargePhoto. The problem is not getting a viewable image; the problem is actually display the viewable image. If you initialize a GridView of List(Of ProductPhoto) to a GridView right now, it looks empty—no image, as illustrated in Figure 1.



Click here for a larger image.

Figure 1: There is no mechanism for assigning an Image field to an Image control (as represented by the Image field in the GridView shown). HTML and web controls want URLs.

Rendering an Image to a UserControl

Now that you have the Image in an object, you have to figure out how to render it. The answer is to insert the image into the HttpResponse stream. You'll add a UserControl to your project and have the UserControl render the image for you (see Listing 3).

Listing 3: You render the graphic to the HttpResponse stream in a UserControl.

Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.IO

Partial Class ImageControl
   Inherits System.Web.UI.UserControl

Protected Sub Page_Load(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Me.Load

   End Sub

   Private FImage As Image
   Public Property TheImage() As Image
      Get
         Return FImage
      End Get
      Set(ByVal value As Image)
         FImage = value
      End Set
   End Property

   Private Sub RenderImage()
#Const BestForGif = True
   If (FImage Is Nothing) Then Return
#If BestForGif Then
      ' this approach seems to work best for gifs - so we are
      ' switching back to a byte array - jpegs can use the code below
      Dim stream As MemoryStream = New MemoryStream()
      FImage.Save(stream, ImageFormat.Gif)
      Response.BinaryWrite(stream.ToArray())
#ElseIf ResolvesGifPoorQuality Then

      ' resolves: "A Graphics object cannot be created from
      ' an image that has an indexed pixel format too" for gifs
      ' but yields a poor result. Use for jpegs or bmps

      Dim b As Bitmap = New Bitmap(FImage.Width, FImage.Height)
      Dim g As Graphics = Graphics.FromImage(b)
      g.DrawImage(FImage, 0, 0)
      Response.ContentType = "image/gif"
      b.Save(Response.OutputStream, ImageFormat.Gif)
      Response.End()

#Else    ' simple for something like gifs

      Response.ContentType = "image/jpeg"
      FImage.Save(Response.OutputStream, IMageFormat.Jpeg)
      Response.End
#End If

   End Sub

   Protected Sub Page_PreRender(ByVal sender As Object, _
      ByVal e As System.EventArgs) Handles Me.PreRender
      RenderImage()
   End Sub
End Class




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