i just would like to be sure whether i missed something in my code or not. I want to validate before moving my files from one folder to another that file is image. I prepared this function and usegae like below. Can you please tell me is it ok? Do i need some dispose or anything else or its just quit enought. many thanks, cheers.
Function IsValidImage(filename As String) As Boolean
Try
Dim img As System.Drawing.Image = System.Drawing.Image.FromFile(filename)
img.Dispose()
Catch generatedExceptionName As OutOfMemoryException
' Image.FromFile throws an OutOfMemoryException
' if the file does not have a valid image format or
' GDI+ does not support the pixel format of the file.
'
Return False
End Try
Return True
End Function
If IsValidImage("c:\path\to\your\file.ext") Then
'do something
'
Else
'do something else
'
End If
Let the file path be "D:\web\sample\Image\my.Image.png" then you can check whether the file is an image file or not using the following code:
Dim filepath As String = "D:\web\sample\Image\my.Image.png"
Dim imageExtensions() As String = {"bmp", "gif", "jpg", "png", "psd", "psp", "thm", "tif", "yuv"}
Dim pat As String = "\\(?:.+)\\(.+)\.(.+)"
Dim r As Regex = New Regex(pat)
Dim m As Match = r.Match(filepath)
If imageExtensions.Contains(m.Groups(2).Captures(0).ToString()) Then
MsgBox("valid Image")
End If
You are on the right way, but you should make up your mind what you want to whant to gain:
If you want to develop a method telling you wheter the content of a file is considered a .Net recognized picture image, your approach is totally fine.
I start with your (slightly) overworked code:
Function IsValidImage(filename As String) As Boolean
Try
Using img As System.Drawing.Image = System.Drawing.Image.FromFile(filename)
' the file could be opened as image so it is valid
Return True
End Using
Catch notValidException As OutOfMemoryException
' Image.FromFile throws an OutOfMemoryException
' if the file does not have a valid image format or
' GDI+ does not support the pixel format of the file.
'
Return False
End Try
' Every other Exception is considered not to be able too look whether the
' file is an Image or not, so it should be thrown to outside
End Function
Don't misjudge this approach as using Exception for control flow, you are only reacting to the one thrown if the content of the file is not usable for creating an Image. This let's the decision on the framework whether the file is valid for an Imageor not.
Let's refine your Method a little bit, so that you can determine wheter the image in the file does not exceed a given size:
Function IsValidImage(filename As String, maxSize As Size) As Boolean
Try
Using img As System.Drawing.Image = System.Drawing.Image.FromFile(filename)
' Returns True if the image is smaller or equal than maxSize
Return img.Size.Width <= maxSize.Width AndAlso
img.Size.Height <= maxSize.Height
End Using
Catch notValidException As OutOfMemoryException
Return False
End Try
End Function
Also this is not a misuse of Exceptions. It is a practice of fail fast: if I can't get an Image the file is not an Image. Otherwise I check the dimension on the opened Image, making my outcome dependent on operations done with it.
Misusing an Exception for control flow could, but must not be the following:
Sub CheckImage(filename As String)
Try
Using img As System.Drawing.Image = System.Drawing.Image.FromFile(filename)
End Using
Catch notValidException As OutOfMemoryException
Throw New FileIsNoImageException()
End Try
End Sub
Try
CheckImage("c:\path\to\your\file.ext")
'do something
'
Catch invalid As FileIsNoImageException
'do something else
'
End Try
Even this approach has a valid usage if you consider a file not beeing an Image as an error.
But normaly you would do this in functions which give you the Image as return value.
But this is a tottaly no go:
Sub CheckImage(filename As String)
Try
Using img As System.Drawing.Image = System.Drawing.Image.FromFile(filename)
Throw New FileIsImageException() ' DON'T DO SUCH A CRAP
End Using
Catch notValidException As OutOfMemoryException
Throw New FileIsNoImageException()
End Try
End Sub
Try
CheckImage("c:\path\to\your\file.ext")
Catch valid As FileIsImageException
'do something
'
Catch invalid As FileIsNoImageException
'do something else
'
End Try
#Tim, I beg your pardon, but I can't hear this Exception use is a bad practice tale any more.
I need download a CSV file and then read it. Here is my code:
tickerValue = "goog"
Dim strURL As String = "http://ichart.yahoo.com/table.csv?s=" & tickerValue
Dim strBuffer As String = RequestWebData(strURL)
Using streamReader = New StreamReader(strBuffer)
Using reader = New CsvReader(streamReader)
I keep getting this error: An unhandled exception of type 'System.ArgumentException' occurred in mscorlib.dll Additional information: Illegal characters in path.
What am I doing wrong?
Additional Info
In another part of my program I use this code and it works fine.
Address = http://www.nasdaq.com/screening/companies-by-industry.aspx?exchange=AMEX&render=download
Dim strBuffer As String = Historical_Stock_Prices.RequestWebData(Address)
Using streamReader = New StringReader(strBuffer)
Using reader = New CsvReader(streamReader)
Isn't my second code the same concept as my problem code?
you are giving it, essentially, a web url. somewhere in your code, it does not support the web url. it could be the streamreader. it could be the CsvReader.
what line of code does this point to?
the best bet is to save the file TO DISK, then read from disk.
UPDATE
here is an example to SAVE to disk:
using writer as new StreamWriter("C:\Test.csv")
writer.Write(strBuffer)
writer.Close()
end using
here is an example to READ from disk:
using strReader as new StreamReader("C:\Test.csv")
' this code is presumably how it works for reading into the CsvReader:
using reader as new CsvReader(strReader)
' now do your thing
end using
strReader.Close()
end using
I have created a report that is based on a business object - this works great. I am now trying to add a button that renders the report directly to PDF (in a winforms application).
I know what I need to do - in code I am creating a ReportViewer, setting the DataSource, specifying the report (it's an embedded resource), then rendering the report into a byte array before using System.IO.File.WriteAllBytes to flush the byte array to disk. One thing I'm hung up on though, is how do I specify the instance of the object properly? I keep getting the "An error has occurred during the report processing" error. In IntelliTrace I can see that an exception is thrown "A data source instance has not been supplied for the data source 'IssRep'" (IssRep is the dataset name in the report. Here is the code:
Dim warning As Warning() = Nothing
Dim streamids As String() = Nothing
Dim mimetype As String = Nothing
Dim encoding As String = Nothing
Dim extension As String = Nothing
Dim viewer As New ReportViewer
Dim bs As New BindingSource
bs.DataSource = issuedet
Dim rds As New ReportDataSource
rds.Value = bs
viewer.LocalReport.DataSources.Add(rds)
viewer.ProcessingMode = ProcessingMode.Local
viewer.LocalReport.ReportEmbeddedResource = "FRSFE.SR.rdlc"
Dim pdfbytes As Byte()
Try
pdfbytes = viewer.LocalReport.Render("PDF", Nothing, mimetype, encoding, extension, streamids, warning)
File.WriteAllBytes("C:\Shared\FRS\SR.PDF", pdfbytes)
Catch ex As Exception
MsgBox(ex.Message)
End Try
I'm pretty sure whatever I'm stuck on is pretty simple as I'm very rusty on .NET but I just can't figure it out!
Try setting rds.Name = "IssRep" before adding it to viewer.LocalReport.DataSources.
I am using following code to put JPG's into a DataGridView's Image cell.
If strFileName.ToLower.EndsWith(".jpg") Then
Dim inImg As Image = Image.FromFile(strFileName)
DataGridView4.Rows.Add()
DataGridView4.Rows(DataGridView4.Rows().Count - 1).Cells(0).Value = inImg
End If
The problem is that I need to save this file from within the program, but i get the message that the file is beeing used by another program.
So i tried to add inImg.Dispose() before the end if, but then the program doesnt display the images anymore in the DataGridView.
How can i add images in the DataGridView without locking them?
thanks
When you use the Image.FromFile(strFileName) method to create the Image, the method locks the file until you release the Image. The exact reason is explained below. And it's why you can't access more than one time to the same image file with this method.
You could instead:
use the Image.FromStream(stream) method.
that you use with a New FileStream or a MemoryStream that you create from the image file.
Here are possible implementation of a custom SafeImageFromFile method that doesn't lock the image file:
Public Shared Function SafeImageFromFile(path As String) As Image
Using fs As New FileStream(path, FileMode.Open, FileAccess.Read)
Dim img = Image.FromStream(fs)
Return img
End using
End Function
Or
Public Shared Function SafeImageFromFile(path As String) As Image
Dim bytes = File.ReadAllBytes(path)
Using ms As New MemoryStream(bytes)
Dim img = Image.FromStream(ms)
Return img
End Using
End Function
Usage
If strFileName.ToLower.EndsWith(".jpg") Then
Dim inImg As Image = SafeImageFromFile(strFileName)
Dim index as integer = DataGridView4.Rows.Add()
DataGridView4.Rows(index).Cells(0).Value = inImg
End If
Important note
Here I create the FileStream or a MemoryStream using a Using statement to make sure the stream is released. It works fine on my system and it seems it work for you too, though MSDN says about Image.FromStream(stream) method:
You must keep the stream open for the lifetime of the Image.
The reason of this sentence is explain here: KB814675 Bitmap and Image constructor dependencies
GDI+, and therefore the System.Drawing namespace, may defer the
decoding of raw image bits until the bits are required by the image.
Additionally, even after the image has been decoded, GDI+ may
determine that it is more efficient to discard the memory for a large
Bitmap and to re-decode later. Therefore, GDI+ must have access to the
source bits for the image for the life of the Bitmap or the Image
object.
To retain access to the source bits, GDI+ locks any source file, and
forces the application to maintain the life of any source stream, for
the life of the Bitmap or the Image object.
So know the code above could generate GDIexceptions because of releasing the stream using Using. It could happen when you save the image from the file or during the image creation. From this thread Loading an image from a stream without keeping the stream open and Hans Passant's comment they fixed several problems with indexed pixel formats in the Vista version of gdiplus.dll., it would happen only on XP.
To avoid this you need to keep the stream open. The methods would be:
Public Shared Function SafeImageFromFile(path As String) As Image
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read)
Dim img = Image.FromStream(fs)
Return img
End Function
Or
Public Shared Function SafeImageFromFile(path As String) As Image
Dim bytes = File.ReadAllBytes(path)
Dim ms = New MemoryStream(bytes)
Dim img = Image.FromStream(ms)
Return img
End Function
But those last methods have some disadvantage like not releasing the stream (memory issue) and they violate rule CA2000 Dispose objects before losing scope .
The KB article gives some workarounds:
Create a Non-Indexed Image
This approach requires that the new image be in a non-indexed pixel
format (more than 8 bits-per-pixel), even if the original image was in
an indexed format. This workaround uses the Graphics.DrawImage()
method to copy the image to a new Bitmap object:
Construct the original Bitmap from the stream, from the memory, or from the file.
Create a new Bitmap of the same size, with a pixel format of more than 8 bits-per-pixel (BPP).
Use the Graphics.FromImage() method to obtain a Graphics object for the second Bitmap.
Use Graphics.DrawImage() to draw the first Bitmap onto the second Bitmap.
Use Graphics.Dispose() to dispose of the Graphics.
Use Bitmap.Dispose() to dispose of the first Bitmap.
Create an Indexed Image
This workaround creates a Bitmap object in an indexed format:
Construct the original Bitmap from the stream, from the memory, or from the file.
Create a new Bitmap with the same size and pixel format as the first Bitmap.
Use the Bitmap.LockBits() method to lock the whole image for both Bitmap objects in their native pixel format.
Use either the Marshal.Copy function or another memory copying function to copy the image bits from the first Bitmap to the second Bitmap.
Use the Bitmap.UnlockBits() method to unlock both Bitmap objects.
Use Bitmap.Dispose() to dispose of the first Bitmap.
Here is an implementation of Non-Indexed Image creation, based on KB article and this answer https://stackoverflow.com/a/7972963/2387010 Your best bet is creating a pixel-perfect replica of the image -- though YMMV (with certain types of images there may be more than one frame, or you may have to copy palette data as well.) But for most images, this works:
Private Shared Function SafeImageFromFile(path As String) As Bitmap
Dim img As Bitmap = Nothing
Using fs As New FileStream(path, FileMode.Open, FileAccess.Read)
Using b As New Bitmap(fs)
img = New Bitmap(b.Width, b.Height, b.PixelFormat)
Using g As Graphics = Graphics.FromImage(img)
g.DrawImage(b, Point.Empty)
g.Flush()
End Using
End Using
End Using
Return img
End Function
Someone indicated that what is important is that the FileStream is opened in read mode (FileAccess.Read).
True, but it makes more sens if you don't use Using statement and so you don't release the stream, or in multi threads context: FileAccess.Write is inappropriate, and FileAccess.ReadWrite is not required, but open the stream with FileAccess.Read mode won't prevent to have an IO.Exception if another program (or yours in multi threads context) has opened the file with another mode than FileAccess.Read.
If you want to be able to display the image and at the same time be able to save data to the file, Since you don't lock the file with those methods, you should be able to save the image (delete/overwrite the previous file) using the Image.Save method.
# Chris: Opening approximately 100 large (3400x2200) images with your final code, I was receiving an invalid argument crash on [img = new bitmap(...], I have seen this before opening an image of zero size, but that was not the case here. I added fs.dispose and successfully opened thousands of images of the same size of the same set as the first test without issue. I'm interested in your comments on this.
Private Function SafeImageFromFile(FilePath As String) As Image
Dim img As Bitmap = Nothing
Using fs As New FileStream(FilePath, FileMode.Open, FileAccess.Read)
Using b As New Bitmap(fs)
img = New Bitmap(b.Width, b.Height, b.PixelFormat)
Using g As Graphics = Graphics.FromImage(img)
g.DrawImage(b, Point.Empty)
g.Flush()
End Using
End Using
fs.Dispose()
End Using
Return img
End Function
This works without issue, ran 4189 images 3400x2200 through it (twice) without issue, this moves the filestream outside of the function and re-uses it. Im closing the file to release the write lock. Im pointing a picturebox at this image in a loop for my test.
Private fsIMG As FileStream
Private Function SafeImageFromFile(FilePath As String) As Image
'Ref: http://stackoverflow.com/questions/18250848/how-to-prevent-the-image-fromfile-method-to-lock-the-file
Dim img As Bitmap = Nothing
fsIMG = New FileStream(FilePath, FileMode.Open, FileAccess.Read)
Using b As New Bitmap(fsIMG)
img = New Bitmap(b.Width, b.Height, b.PixelFormat)
Using g As Graphics = Graphics.FromImage(img)
g.DrawImage(b, Point.Empty)
g.Flush()
End Using
End Using
fsIMG.Close()
Return img
End Function
After searching the internet for long time I found out I can use this code without any error.
Private fsIMG As FileStream
Private Function SafeImageFromFile(FilePath As String) As Image
'Ref: http://stackoverflow.com/questions/18250848/how-to-prevent-the-image-fromfile-method-to-lock-the-file
Dim img As Bitmap = Nothing
fsIMG = New FileStream(FilePath, FileMode.Open, FileAccess.Read)
Using b As New Bitmap(fsIMG)
img = New Bitmap(b.Width, b.Height, b.PixelFormat)
Using g As Graphics = Graphics.FromImage(img)
g.DrawImage(b, Point.Empty)
g.Flush()
End Using
End Using
fsIMG.Close()
Return img
End Function
I encountered the same situation and used this code:
' Create memory stream from file
Dim ms As New MemoryStream()
' Open image file
Using fs As New FileStream(.FileName, FileMode.Open, FileAccess.Read)
' Save to memory stream
fs.CopyTo(ms)
End Using
' Create image from the file's copy in memory
Dim img = Image.FromStream(ms)
I didn't dispose the memory stream because it allows to save the image later using exactly the same encoding as the original file, using this code:
img.Save(someOtherStream, img.RawFormat)
I am coding a whitelist for my application in VB.NET.
I am using the HttpWebRequest Method and HttpWebResponse.
If the Whitelist Host is down, the whitelist is bypassed and the program is available to anyone which is a vulnerability.
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Try
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Catch ex As Exception
Debug.WriteLine("Start Program Error. Handle:0")
End Try
Return S
End Function
I want to give the user an error if the website is down, any ideas?
Regards.
What is your error condition? This function alone doesn't prevent anything from happening in the event of an exception. The function still exits with returning a string. So any consuming code would have to look for error conditions and handle them accordingly.
If the request fails, you should meaningfully handle the exception. Two ideas off the top of my head would include:
1) Let the exception bubble up the stack:
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Return S
End Function
This would make the attempt to contact the host and, if that attempt failed, throw an exception instead of return a string.
2) Throw a custom exception:
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Try
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Catch ex As Exception
Debug.WriteLine("Start Program Error. Handle:0")
Throw New SomeCustomException(String.Format("Unable to contact host: {0}", PageURL), ex)
End Try
Return S
End Function
This would provide a more targeted exception instead of whatever comes out of the response reader, would provide useful runtime information about the error for logging and analysis (namely the runtime value of the PageURL), and takes a step toward hiding the implementation details from code outside of this object (since that code doesn't really care about the HttpWebRequest and HttpWebResponse, it just wants to know if the URL is good or not).
Remember that throwing an exception is a perfectly acceptable exit path for a function. It doesn't always have to return a value. An exception is an appropriate way of indicating an error condition. Your current implementation, however, "swallows" the exception and provides no indication to the consuming code that anything went wrong. Instead it returns a "magic value" of String.Empty which consuming code may or may not ignore.
Change your exception handler. The correct way to do this is to just try the request and handle the exception if it fails.