Sharing violation (Desktop)

alfcen

Well-Known Member
Licensed User
Longtime User
Situation:
1. download an image via http.dll
2. save the image using the binary.dll and properly close the file
3. draw the saved image on a form
4. download the same image again for a refresh

The newly downloaded image can't be saved with the same name because
Windows throws an error: "The file may be use by another process..."
I would assume that a properly closed file can be overwritten.
Curiously, this does not happen every time (but too often).

Any thoughts are welcome
 

Erel

B4X founder
Staff member
Licensed User
Longtime User
The problem is between steps 3 and 4.
When you draw an image from a file the file gets locked.
One solution is to first load the image to a Bitmap object and then draw the Bitmap object.
However you can draw the image without saving it at all by using the Door library:
http://www.b4x.com/forum/showpost.php?p=11017&postcount=2
 

alfcen

Well-Known Member
Licensed User
Longtime User
Thanks for your fast response, Erel

Actually, the error happens at FileOpen when I download a second time
and save with the same file name (var LocalFile), irrespective of whether
the image is drawn on a form or not.

Looks like the image file the Writer object creates gets locked when
completely saved.

I was hoping to work around without additional DLLs. The image needs
to be saved for offline viewing.

B4X: 
  Response.New1
  Request.New1(URL)
  Request.TimeOut = 60000
  Response.Value = Request.GetResponse
  Reader.New1(Response.GetStream,true)
  FileOpen(c1,LocalFile,cRandom)
  Writer.New1(c1,false)
  Dim buffer(4096) As byte
  count = Reader.ReadBytes(buffer(),4096)
  Do While count > 0
    Writer.WriteBytes2(buffer(),0,count)
    count = Reader.ReadBytes(buffer(),4096)
  Loop
  FileClose(c1)     
  Response.Close
  ' DisplayImage(LocalFile, wf, hf, sf)   'The image is drawn on the form here. Error persists if I REM this line
 

Erel

B4X founder
Staff member
Licensed User
Longtime User
The following code works properly here:
B4X: 
Sub App_Start
For i = 1 To 2
    Response.New1
  Request.New1("http://www.b4x.com/index.html")
  Request.TimeOut = 60000
  Response.Value = Request.GetResponse
  Reader.New1(Response.GetStream,true)
  FileOpen(c1,"1.txt",cRandom)
  Writer.New1(c1,false)
  Dim buffer(4096) As byte
  count = Reader.ReadBytes(buffer(),4096)
  Do While count > 0
    Writer.WriteBytes2(buffer(),0,count)
    count = Reader.ReadBytes(buffer(),4096)
  Loop
  FileClose(c1)     
  Response.Close
Next
End Sub
 
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