In This Topic
You should do the following steps if you want to cancel image acquisition:
- 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 you
are 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 image acquisition process
(instead of cancelling image acquisition) if you need to keep all acquired images.
Here is an example that demonstrates how to cancel current asynchronous image transfer:
namespace TwainExamples_CSharp
{
class AsyncScan_Cancel
{
static bool _isScanFinished;
static bool _isScanCanceled;
/// <summary>
/// This method scans one image and cancels image scan.
/// </summary>
public static void ScanOneImageAndCancelScan()
{
_isScanFinished = 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 (!_isScanFinished)
{
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)
{
_isScanFinished = true;
}
}
}
Class AsyncScan_Cancel
Shared _isScanFinished As Boolean
Shared _isScanCanceled As Boolean
''' <summary>
''' This method scans one image and cancels image scan.
''' </summary>
Public Shared Sub ScanOneImageAndCancelScan()
_isScanFinished = 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 ApplicationException(String.Format("Device '{0}' is not found.", deviceName))
End If
' subscribe to device events
AddHandler device.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
AddHandler device.ScanCompleted, New EventHandler(AddressOf device_ScanCompleted)
AddHandler device.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
AddHandler device.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
AddHandler device.ScanFinished, New 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 _isScanFinished
System.Windows.Forms.Application.DoEvents()
End While
If Not _isScanCanceled Then
Throw New ApplicationException("Scan is NOT canceled.")
End If
' unsubscribe from device events
RemoveHandler device.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
RemoveHandler device.ScanCompleted, New EventHandler(AddressOf device_ScanCompleted)
RemoveHandler device.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
RemoveHandler device.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
RemoveHandler device.ScanFinished, New EventHandler(AddressOf device_ScanFinished)
' close the device
device.Close()
End Using
End Sub
Private Shared Sub device_ImageAcquired(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiredEventArgs)
Console.WriteLine("Image is acquired.")
' get reference to the device
Dim device As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)
' cancel image scan
device.CancelTransfer()
End Sub
Private Shared Sub device_ScanCompleted(ByVal sender As Object, ByVal e As EventArgs)
Console.WriteLine("Scan is completed.")
End Sub
Private Shared Sub device_ScanCanceled(ByVal sender As Object, ByVal e As EventArgs)
_isScanCanceled = True
Console.WriteLine("Scan is canceled.")
End Sub
Private Shared Sub device_ScanFailed(ByVal sender As Object, ByVal e As Vintasoft.Twain.ScanFailedEventArgs)
Console.WriteLine(String.Format("Scan is failed: {0}.", e.ErrorString))
End Sub
Private Shared Sub device_ScanFinished(ByVal sender As Object, ByVal e As EventArgs)
_isScanFinished = True
End Sub
End Class
Here is an example that demonstrates how to cancel current synchronous image transfer:
namespace TwainExamples_CSharp
{
class SyncScan_Cancel
{
/// <summary>
/// This method scans one image and cancels image scan.
/// </summary>
public static void ScanOneImageAndCancelScan()
{
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();
}
}
}
}
Class SyncScan_Cancel
''' <summary>
''' This method scans one image and cancels image scan.
''' </summary>
Public Shared Sub ScanOneImageAndCancelScan()
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 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 acquireModalState1 As Vintasoft.Twain.AcquireModalState = Vintasoft.Twain.AcquireModalState.None
Do
acquireModalState1 = device.AcquireModal()
Select Case acquireModalState1
Case Vintasoft.Twain.AcquireModalState.ImageAcquired
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
Console.WriteLine("Scan is completed.")
Exit Select
Case Vintasoft.Twain.AcquireModalState.ScanCanceled
isScanCanceled = True
Console.WriteLine("Scan is canceled.")
Exit Select
Case Vintasoft.Twain.AcquireModalState.ScanFailed
Console.WriteLine(String.Format("Scan is failed: {0}.", device.ErrorString))
Exit Select
End Select
Loop While acquireModalState1 <> Vintasoft.Twain.AcquireModalState.None
If Not isScanCanceled Then
Throw New ApplicationException("Scan is NOT canceled.")
End If
' close the device
device.Close()
End Using
End Sub
End Class