Usage of streams

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Usage of streams

Post by serrut » Fri Jun 07, 2013 09:04 AM

Hi,

What is the best practise for viewing & modifying images in a Vintasoft ImageViewer component?

Do I need to keep the stream to the image open or close it?

In the documentation I found following code:

Dim images As ImageCollection = New ImageCollection()
Dim fStream As FileStream = New FileStream("multipage.tif", FileMode.Open, FileAccess.ReadWrite)
Dim images As ImageCollection images = New ImageCollection
images.Add(fStream)

If I close the file stream, an exception (below you can find the trace) occurs in the ImageViewer component: cannot access a closed file.
As I use a lot of ImageViewer components in my application gui, I need to keep a lot of streams open, which I don't like!

   at System.IO.__Error.FileNotOpen()
   at System.IO.FileStream.Seek(Int64 offset, SeekOrigin origin)
   at System.IO.FileStream.set_Position(Int64 value)
   at Vintasoft.Imaging.Codecs.ImageFileSource.set_Position(Int64 value)
   at Vintasoft.Imaging.Codecs.Tiff.TiffTag.()
   at ..()
   at ..()
   at Vintasoft.Imaging.Codecs.Tiff.TiffPage.GetStripGrid()
   at Vintasoft.Imaging.Codecs.TiffDecoder.GetImageRectGrid(Int32 pageIndex)
   at Vintasoft.Imaging.ImageRendering.ImageRenderer..ctor(DecoderBase decoder, Int32 pageIndex)
   at Vintasoft.Imaging.ImageRendering.ImageRenderer..ctor(VintasoftImage image)
   at ..6(VintasoftImage )
   at Vintasoft.Imaging.ImageViewer.(VintasoftImage , Boolean )
   at Vintasoft.Imaging.ImageViewer.(VintasoftImage , Boolean )
   at ..81()
   at ..()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Thanks for your replies.

Re: Usage of streams

Post by Alex » Fri Jun 07, 2013 10:26 AM

Hello Tom,

If you want to view and modify images from files in the ImageViewer, the best practice is

1. Open file in read-write mode and get reference to the image stream

Dim fStream As FileStream = New FileStream("multipage.tif", FileMode.Open, FileAccess.ReadWrite)

2. Add image stream to the image collection of ImageViewer

imageViewer1.Images.Add(fStream)

3. View and modify images in image collection of ImageViewer

imageViewer1.Images(0).Rotate(90)

4. Remove image from collection and close the image stream when image is not necessary any more

For i = 0 To imageViewer1.Images.Count - 1
  imageViewer1.Images(i).SourceInfo.Stream.Close()
Next i

imageViewer1.Images.ClearAndDisposeItems()

Best regards, Alexander

Re: Usage of streams

Post by serrut » Fri Jun 07, 2013 11:41 AM

Hi Alex,

Thank you for your answer. Your code helps me to not store the stream in my object, which I like.
BUT ... if I have 100 ImageViewers, I still have 100 file streams open. Right?

I have always learned to close a stream as soon as possible. If you want to modify again, just initialize (open) the stream again, do the modification and close it again ...

In a previous version of Vintasoft Imaging (4.3), the internal logic must have been different:

Dim image as VintaSoftImage = new VintaSoftImage("C:/temp/test.tiff")
imageViewer.Image = image

This code block was working perfectly, and no lock was left on my file. This is expected behavior. But since 6.1, the lock on the file stays ...

Re: Usage of streams

Post by serrut » Fri Jun 07, 2013 12:01 PM

I also want to notice we add ImageViewer's dynamically to our VB.NET application form. Images are retrieved from a scanner, or a file import (PDF for example).
I just created a test project which has a form and a button "btnAddImageViewer". When you click the button, the application will crash => "Cannot access a closed file"

 Private Sub btnAddImageViewer_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddImageViewer.Click
        ' Create image viewer
        Dim imageViewer As ImageViewer = New ImageViewer()
        imageViewer.Location = New Point(100, 100)
        imageViewer.Size = New Size(200, 200)

        ' Add image to image viewer
        Dim fstream As FileStream = Nothing
        Try
            fstream = New FileStream("c:/temp/test.tiff", FileMode.Open, FileAccess.Read)
            imageViewer.Images.Add(fstream)
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            If (fstream IsNot Nothing) Then
                Try
                    fstream.Close()
                Catch ex As Exception
                    MsgBox(ex.Message)
                End Try
            End If
        End Try

        ' Add image viewer to form
        Me.Controls.Add(imageViewer)
    End Sub

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