Acquire images asynchronously

VintaSoft Twain ActiveX allows to acquire images from the scanner asynchronously.

Here is to do list for acquiring images asynchronously:

Open TWAIN device manager.
Select TWAIN device.
Subscribe to the events of TWAIN device: Device_ImageAcquired, Device_ScanCompleted, etc.
Open TWAIN device.
Set the scanning settings.
Start the asynchronous acquisition process.
Retrieve acquired image one by one while the Device_ImageAcquired event fires.
Stop image acquisition process when the Device_ScanCompleted event fires.

Example: Here is an example that shows how to acquire images asynchronously using scanner driver user interface and save acquired images into multipage TIFF file:

VB.NET

Private VSTwain1 As New VintaSoftTwain()


''' <summary>
''' Scans images asynchronously.
''' </summary>
Private Sub ScanImages()
    ' specify name of scanning application
    VSTwain1.DeviceManager_ApplicationProductName = "MyTwainApplication"
    ' open the device manager
    If Not VSTwain1.DeviceManager_Open() Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' select device using standard device selection dialog
    VSTwain1.DeviceManager_ShowDefaultDeviceSelectionDialog()

    ' open the device
    If Not VSTwain1.Device_Open Then
        Console.WriteLine(VSTwain1.errorString)
        Exit Sub
    End If

    ' specify that device UI must be shown
    VSTwain1.Device_ShowUI = True

    ' specify that acquired image must be added to an existing TIFF file
    VSTwain1.TiffEncoder_MultiPage = True

    ' subscribe to the device events
    AddHandler VSTwain1.DeviceImageAcquired, AddressOf VSTwain1_ImageAcquired
    AddHandler VSTwain1.DeviceScanCompleted, AddressOf VSTwain1_ScanCompleted
    AddHandler VSTwain1.DeviceScanFailed, AddressOf VSTwain1_ScanFailed
    AddHandler VSTwain1.DeviceScanCanceled, AddressOf VSTwain1_ScanCanceled

    ' acquire images asynchronously
    VSTwain1.Device_AcquireImage()
End Sub

Private Sub VSTwain1_ImageAcquired()
    ' get index of acquired image
    Dim imageIndex As Integer = VSTwain1.AcquiredImages_Count - 1

    ' save acquired image to TIFF file
    If Not VSTwain1.AcquiredImages_Save(imageIndex, "test.tif") Then
        Console.WriteLine(VSTwain1.errorString)
    End If
End Sub

Private Sub VSTwain1_ScanCompleted()
    Console.WriteLine("Scan is completed.")
End Sub

Private Sub VSTwain1_ScanFailed(errorString As String)
    Console.WriteLine(String.Format("Scan is failed: {0}.", errorString))
End Sub

Private Sub VSTwain1_ScanCanceled()
    Console.WriteLine("Scan is canceled.")
End Sub

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