Cancel acqusition of images from TWAIN device
In This Topic
You should do the following steps if you want to cancel acquisition of image from TWAIN device:
- Call the Device.CancelTransfer method.
- Wait for the Device.ScanCanceled event if you are acquiring images asynchronously.
- Wait while the Device.AcquireModal method returns AcquireModalState.ScanCanceled if youare acquiring images in modal loop.
Some high speed TWAIN scanners have internal buffer and TWAIN scanners cache the acquired images in the buffer if TWAIN scanner is faster than application which processes acquired images. Images, which are cached in internal buffer, will be lost if you cancel the image acquisition process. You can
pause TWAIN image acquisition process (instead of cancelling TWAIN image acquisition) if you need to keep all acquired images.
Here is an example that demonstrates how to cancel current asynchronous acquisition of images from TWAIN device:
static bool _isScanningFinished;
static bool _isScanCanceled;
/// <summary>
/// Asynchronously acquires one image from TWAIN device and cancels image transfer.
/// </summary>
public static void AsynchronouslyAcquireImageFromTwainDeviceAndCancelImageTransfer()
{
_isScanningFinished = false;
_isScanCanceled = false;
// create the device manager
using (Vintasoft.Twain.DeviceManager deviceManager = new Vintasoft.Twain.DeviceManager())
{
deviceManager.IsTwain2Compatible = true;
// open the device manager
deviceManager.Open();
// get the device
string deviceName = "KODAK Scanner: i5000";
Vintasoft.Twain.Device device = deviceManager.Devices.Find(deviceName);
if (device == null)
throw new System.ApplicationException(string.Format("Device '{0}' is not found.", deviceName));
// subscribe to device events
device.ImageAcquired += new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
device.ScanCompleted += new System.EventHandler(device_ScanCompleted);
device.ScanCanceled += new System.EventHandler(device_ScanCanceled);
device.ScanFailed += new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
device.ScanFinished += new System.EventHandler(device_ScanFinished);
// disable device UI
device.ShowUI = false;
// specify that device must be closed after scan
device.DisableAfterAcquire = true;
// open the device
device.Open();
// specify that 2 images must be acquired from scanner
device.XferCount = 2;
// run asynchronous image acqusition
device.Acquire();
// wait while scan will be finished
while (!_isScanningFinished)
{
System.Windows.Forms.Application.DoEvents();
}
if (!_isScanCanceled)
throw new System.ApplicationException("Scan is NOT canceled.");
// unsubscribe from device events
device.ImageAcquired -= new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
device.ScanCompleted -= new System.EventHandler(device_ScanCompleted);
device.ScanCanceled -= new System.EventHandler(device_ScanCanceled);
device.ScanFailed -= new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
device.ScanFinished -= new System.EventHandler(device_ScanFinished);
// close the device
device.Close();
}
}
static void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
{
// get reference to the device
Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;
// cancel image scan
device.CancelTransfer();
System.Console.WriteLine("Feeder is stopped.");
}
static void device_ScanCompleted(object sender, System.EventArgs e)
{
System.Console.WriteLine("Scan is completed.");
}
static void device_ScanCanceled(object sender, System.EventArgs e)
{
_isScanCanceled = true;
System.Console.WriteLine("Scan is canceled.");
}
static void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
{
System.Console.WriteLine(string.Format("Scan is failed: {0}.", e.ErrorString));
}
static void device_ScanFinished(object sender, System.EventArgs e)
{
_isScanningFinished = true;
}
Shared _isScanningFinished As Boolean
Shared _isScanCanceled As Boolean
''' <summary>
''' Asynchronously acquires one image from TWAIN device and cancels image transfer.
''' </summary>
Public Shared Sub AsynchronouslyAcquireImageFromTwainDeviceAndCancelImageTransfer()
_isScanningFinished = False
_isScanCanceled = False
' create the device manager
Using deviceManager As New Vintasoft.Twain.DeviceManager()
deviceManager.IsTwain2Compatible = True
' open the device manager
deviceManager.Open()
' get the device
Dim deviceName As String = "KODAK Scanner: i5000"
Dim device As Vintasoft.Twain.Device = deviceManager.Devices.Find(deviceName)
If device Is Nothing Then
Throw New System.ApplicationException(String.Format("Device '{0}' is not found.", deviceName))
End If
' subscribe to device events
AddHandler device.ImageAcquired, New System.EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
AddHandler device.ScanCompleted, New System.EventHandler(AddressOf device_ScanCompleted)
AddHandler device.ScanCanceled, New System.EventHandler(AddressOf device_ScanCanceled)
AddHandler device.ScanFailed, New System.EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
AddHandler device.ScanFinished, New System.EventHandler(AddressOf device_ScanFinished)
' disable device UI
device.ShowUI = False
' specify that device must be closed after scan
device.DisableAfterAcquire = True
' open the device
device.Open()
' specify that 2 images must be acquired from scanner
device.XferCount = 2
' run asynchronous image acqusition
device.Acquire()
' wait while scan will be finished
While Not _isScanningFinished
System.Windows.Forms.Application.DoEvents()
End While
If Not _isScanCanceled Then
Throw New System.ApplicationException("Scan is NOT canceled.")
End If
' unsubscribe from device events
RemoveHandler device.ImageAcquired, New System.EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
RemoveHandler device.ScanCompleted, New System.EventHandler(AddressOf device_ScanCompleted)
RemoveHandler device.ScanCanceled, New System.EventHandler(AddressOf device_ScanCanceled)
RemoveHandler device.ScanFailed, New System.EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
RemoveHandler device.ScanFinished, New System.EventHandler(AddressOf device_ScanFinished)
' close the device
device.Close()
End Using
End Sub
Private Shared Sub device_ImageAcquired(sender As Object, e As Vintasoft.Twain.ImageAcquiredEventArgs)
' get reference to the device
Dim device As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)
' cancel image scan
device.CancelTransfer()
System.Console.WriteLine("Feeder is stopped.")
End Sub
Private Shared Sub device_ScanCompleted(sender As Object, e As System.EventArgs)
System.Console.WriteLine("Scan is completed.")
End Sub
Private Shared Sub device_ScanCanceled(sender As Object, e As System.EventArgs)
_isScanCanceled = True
System.Console.WriteLine("Scan is canceled.")
End Sub
Private Shared Sub device_ScanFailed(sender As Object, e As Vintasoft.Twain.ScanFailedEventArgs)
System.Console.WriteLine(String.Format("Scan is failed: {0}.", e.ErrorString))
End Sub
Private Shared Sub device_ScanFinished(sender As Object, e As System.EventArgs)
_isScanningFinished = True
End Sub
Here is an example that demonstrates how to cancel current synchronous acquisition of images from TWAIN device:
/// <summary>
/// Synchronously acquires one image from TWAIN device and cancels image transfer.
/// </summary>
public static void SynchronouslyAcquireImageFromTwainDeviceAndCancelImageTransfer()
{
bool isScanCanceled = false;
// create the device manager
using (Vintasoft.Twain.DeviceManager deviceManager = new Vintasoft.Twain.DeviceManager())
{
deviceManager.IsTwain2Compatible = true;
// open the device manager
deviceManager.Open();
// get the device
string deviceName = "KODAK Scanner: i5000";
Vintasoft.Twain.Device device = deviceManager.Devices.Find(deviceName);
if (device == null)
throw new System.ApplicationException(string.Format("Device '{0}' is not found.", deviceName));
// disable device UI
device.ShowUI = false;
// specify that device must be closed after scan
device.DisableAfterAcquire = true;
// open the device
device.Open();
// specify that 2 images must be acquired from scanner
device.XferCount = 2;
// run asynchronous image acquisition
Vintasoft.Twain.AcquireModalState acquireModalState = Vintasoft.Twain.AcquireModalState.None;
do
{
acquireModalState = device.AcquireModal();
switch (acquireModalState)
{
case Vintasoft.Twain.AcquireModalState.ImageAcquired:
System.Console.WriteLine("Image is acquired.");
if (device.AcquiredImage != null)
device.AcquiredImage.Dispose();
// cancel image scan
device.CancelTransfer();
break;
case Vintasoft.Twain.AcquireModalState.ScanCompleted:
System.Console.WriteLine("Scan is completed.");
break;
case Vintasoft.Twain.AcquireModalState.ScanCanceled:
isScanCanceled = true;
System.Console.WriteLine("Scan is canceled.");
break;
case Vintasoft.Twain.AcquireModalState.ScanFailed:
System.Console.WriteLine(string.Format("Scan is failed: {0}.", device.ErrorString));
break;
}
}
while (acquireModalState != Vintasoft.Twain.AcquireModalState.None);
if (!isScanCanceled)
throw new System.ApplicationException("Scan is NOT canceled.");
// close the device
device.Close();
}
}
''' <summary>
''' Synchronously acquires one image from TWAIN device and cancels image transfer.
''' </summary>
Public Shared Sub SynchronouslyAcquireImageFromTwainDeviceAndCancelImageTransfer()
Dim isScanCanceled As Boolean = False
' create the device manager
Using deviceManager As New Vintasoft.Twain.DeviceManager()
deviceManager.IsTwain2Compatible = True
' open the device manager
deviceManager.Open()
' get the device
Dim deviceName As String = "KODAK Scanner: i5000"
Dim device As Vintasoft.Twain.Device = deviceManager.Devices.Find(deviceName)
If device Is Nothing Then
Throw New System.ApplicationException(String.Format("Device '{0}' is not found.", deviceName))
End If
' disable device UI
device.ShowUI = False
' specify that device must be closed after scan
device.DisableAfterAcquire = True
' open the device
device.Open()
' specify that 2 images must be acquired from scanner
device.XferCount = 2
' run asynchronous image acquisition
Dim acquireModalState As Vintasoft.Twain.AcquireModalState = Vintasoft.Twain.AcquireModalState.None
Do
acquireModalState = device.AcquireModal()
Select Case acquireModalState
Case Vintasoft.Twain.AcquireModalState.ImageAcquired
System.Console.WriteLine("Image is acquired.")
If device.AcquiredImage IsNot Nothing Then
device.AcquiredImage.Dispose()
End If
' cancel image scan
device.CancelTransfer()
Exit Select
Case Vintasoft.Twain.AcquireModalState.ScanCompleted
System.Console.WriteLine("Scan is completed.")
Exit Select
Case Vintasoft.Twain.AcquireModalState.ScanCanceled
isScanCanceled = True
System.Console.WriteLine("Scan is canceled.")
Exit Select
Case Vintasoft.Twain.AcquireModalState.ScanFailed
System.Console.WriteLine(String.Format("Scan is failed: {0}.", device.ErrorString))
Exit Select
End Select
Loop While acquireModalState <> Vintasoft.Twain.AcquireModalState.None
If Not isScanCanceled Then
Throw New System.ApplicationException("Scan is NOT canceled.")
End If
' close the device
device.Close()
End Using
End Sub