Updating a Gauge and Detecting a User Interrupt (Visual Basic)

Take the following steps to update a gauge during processing and detect a user interrupt:

1.	Start with the project that you created in Loading and Displaying an Image.
2.	Add the LEAD RasterProcess Object Library to your project.
	On the Project pull-down menu, use the References option, and select the LEAD RasterProcess Object Library (14.5).
3.	$image\btncmd.gif$ Select the CommandButton control; then add the control to your main form. Put the control at the top of the form to keep it away from the image.
4.	In the Properties box, change the CommandButton control's Caption property to Do Median.
5.	$image\btncmd.gif$ Select the CommandButton control; then add another control to your main form. Put the control at the top of the form to keep it away from the image.
6.	In the Properties box, change the CommandButton control's Caption property to Quit.
7.	Build a gauge consisting of a horizontal line $image\btnline.gif$ (Line1) inside a rectangle $image\btnshape.gif$ (Shape1). Put the gauge at the top of the form next to the Quit button.
8.	Add the following code to the general declarations:

Dim fEscape As Integer 'Use to indicate the user interrupt
Dim fInProc As Integer 'Use to avoid closing the form during processing
Public WithEvents RasterProc As LEADRasterProcess

9.	Now, add the following to the Form's Load event to create the ILEADRasterProcess object

'Create the RasterProcess Object
Set RasterProc = CreateObject("LEADRasterProcess.LEADRasterProcess. ")

10.	Add the following code to the first CommandButton control's Click procedure:

Private Sub Command1_Click ()
    'Enable the ProgressStatus event
    RasterProc.EnableProgressEvent = True
    'Initialize the indicators
    fEscape = False 'The user does not want to quit
    fInProc = True 'Processing is taking place
    'Perform a relatively slow median filter
    RasterProc.Median LEADRasterView1.Raster, 4
    'Clean up
    fInProc = False 'Processing is no longer taking place
    LEADRasterView1.ForceRepaint
End Sub

11.	Add the following code to handle the RasterProc object's ProgressStatus procedure:

RasterProc_ProgressStatus(ByVal iPercent As Integer)
    Dim LineLength
    DoEvents 'Detect Windows events
    If Not fEscape Then ' Look for the Click on the Quit button
      LineLength = Form1.Shape1.Width * iPercent / 100 'Udpate the gauge
      Me.Line1.X1 = Me.Shape1.Left
      Me.Line1.X2 = Me.Line1.X1 + LineLength
    Else
      RasterProc.EnableProgressEvent = False 'Cancel the task
    End If
End Sub

12.	Add the following code to the second CommandButton control's Click procedure:

Private Sub Command2_Click ()
fEscape = True 'The user wants to quit
Me.Line1.X2 = Me.Line1.X1 'Set the gauge back to the beginning
End Sub

13.	Add the following code to the main form's QueryUnload procedure:

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
  If fInProc Then 'If processing is taking place
    Cancel = 1 'Do not let the user close the form
  End If
End Sub

14.	Run your program to test it.