I have a form where the user can first scan to a bitmap. When scan is done, and the bitmap is loaded, I have 4 text boxes that are then enabled. Next to each text box, I have a button called "Cut from image". When the user clicks the button, they can click and drag in the bitmap to get the selected text using MODI.
This works perfect except for one annoying bug: When I click a "Cut from image" button and drag a square, it gets the information nicely to the text box. Then, if i click to the next text box, it goes very well, but if I use the tab key to leave the field, I get a "Parameter is not valid"
ArgumentException
Protected Overrides Function ProcessTabKey(ByVal forward As Boolean) As Boolean
MsgBox("TAB is currently disabled!")
Return False 'Tried True as well, just in case
End Function
ArgumentException
Dim filename As Collection
filename = TwainHandler.ScanImages("c:\scan\", "tif")
Dim ScannedFile As Image = Image.FromFile(filename(1))
PictureBox1.Image = ScannedFile
PictureBox1.Width = ScannedFile.Width
' etc.
Your problem is likely that, at some point, you are calling the Dispose
method on one of your Image
objects. When you call Image.Dispose
, it deletes the underlying image data from memory, so the Image
object still exists, but is invalid because it no longer contains an actual image. When you set the PictureBox.Image
property to a loaded Image
object, the PictureBox
control assumes that the Image
object will remain valid so that it can reuse it later any time the control needs to repaint itself to the screen. For instance:
Dim myImage As Image = Image.FromFile("file path")
PictureBox1.Image = myImage
PictureBox1.Refresh() ' This works
myImage.Dispose()
PictureBox1.Refresh() ' This throws an exception because it tries to access the disposed Image object
The PictureBox
control will automatically dispose of the image for you when it is disposed, so you don't need to worry about disposing it yourself. The only time you should be disposing your images is when you are not giving them to any other objects for later use.