VintaSoft Twain .NET SDK 15.0: Documentation for .NET developer
In This Topic
    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:
    1. Call the Device.CancelTransfer method.
    2. Wait for the Device.ScanCanceled event if you are acquiring images asynchronously.
    3. 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