TransformChanged Event

This event is raised when the transformation matrix of the view or any of the item changes by either a programmatic modification or end-user interaction through the user interface.

The event is raised by the UpdateTransform method after all the calculations needed is performed, it gives the user a chance for a catch all notification when anything in the viewer changes.

For more information, refer to Image Viewer Items, Image Viewer Transformation, Image Viewer Bounds and Transform and Image Viewer Layouts.

EventArgs

This example will hook to the TransformChanged event of the viewer and track the current first and largest visible items.

Run the demo, click the Example button and notice that as you pan and zoom the viewer, the values are displayed in the label.

Start with the ImageViewer example, remove all the code inside the example function (search for the "// TODO: add example code here" comment) and insert the following code:

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Imports Leadtools
Imports Leadtools.Controls
Imports Leadtools.Codecs
Imports Leadtools.Drawing
Imports Leadtools.ImageProcessing
Imports Leadtools.ImageProcessing.Color

' Clear all the images already the viewer
_imageViewer.Items.Clear()
' Use vertical view layout
_imageViewer.ViewLayout = New ImageViewerVerticalViewLayout()
' Make sure the item size is larger than the image size (thumbnails mode)
_imageViewer.ItemSize = LeadSize.Create(200, 200)
_imageViewer.ItemPadding = New Padding(8, 8, 8, 20)
_imageViewer.ItemBorderThickness = 1
_imageViewer.ImageBorderThickness = 1
' Add 4 items to the viewer
Using codecs As New RasterCodecs()
   For page As Integer = 1 To 4
      Dim item As New ImageViewerItem()
      Dim fileName As String = Path.Combine(ImagesPath.Path, String.Format("ocr{0}.tif", page))

      ' Create a thumbnail from the image
      Using image As RasterImage = codecs.Load(fileName, page)
         item.Image = image.CreateThumbnail(180, 180, 24, RasterViewPerspective.TopLeft, RasterSizeFlags.Resample)
      End Using

      item.Text = String.Format("Item {0}", page - 1)
      _imageViewer.Items.Add(item)
   Next page
End Using

' Hook to the TransformChanged event that shows occur whenever we pan or zoom
AddHandler _imageViewer.TransformChanged,
Sub(sender, e)
   ' Get the GetFirstVisibleItem and largest
   Dim firstVisible As ImageViewerItem = _imageViewer.GetFirstVisibleItem(ImageViewerItemPart.Item)
   Dim largest As ImageViewerItem = _imageViewer.GetLargestVisibleItem(ImageViewerItemPart.Item)

   ' Show both in the label
   If Not firstVisible Is Nothing Then
      If Not largest Is Nothing Then
         _label.Text = String.Format("First visible {0} - Largest {1}", firstVisible.Text, largest.Text)
      Else
         _label.Text = String.Format("First visible {0} - Largest {1}", firstVisible.Text, "none")
      End If
   Else
      If Not largest Is Nothing Then
         _label.Text = String.Format("First visible {0} - Largest {1}", "none", largest.Text)
      Else
         _label.Text = String.Format("First visible {0} - Largest {1}", "none", "none")
      End If
   End If

using Leadtools;
using Leadtools.Controls;
using Leadtools.Codecs;
using Leadtools.Drawing;
using Leadtools.ImageProcessing;
using Leadtools.ImageProcessing.Color;

// Clear all the images already the viewer
_imageViewer.Items.Clear();
// Use vertical view layout
_imageViewer.ViewLayout = new ImageViewerVerticalViewLayout();
// Make sure the item size is larger than the image size (thumbnails mode)
_imageViewer.ItemSize = LeadSize.Create(200, 200);
_imageViewer.ItemPadding = new Padding(8, 8, 8, 20);
_imageViewer.ItemBorderThickness = 1;
_imageViewer.ImageBorderThickness = 1;
// Add 4 items to the viewer
using (var codecs = new RasterCodecs())
{
   for (var page = 1; page <= 4; page++)
   {
      var item = new ImageViewerItem();
      var fileName = Path.Combine(ImagesPath.Path, string.Format("ocr{0}.tif", page));

      // Create a thumbnail from the image
      using (var image = codecs.Load(fileName, page))
      {
         item.Image = image.CreateThumbnail(180, 180, 24, RasterViewPerspective.TopLeft, RasterSizeFlags.Resample);
      }

      item.Text = string.Format("Item {0}", page - 1);
      _imageViewer.Items.Add(item);
   }
}

// Hook to the TransformChanged event that shows occur whenever we pan or zoom
_imageViewer.TransformChanged += (sender, e) =>
{
   // Get the GetFirstVisibleItem and largest
   var firstVisible = _imageViewer.GetFirstVisibleItem(ImageViewerItemPart.Item);
   var largest = _imageViewer.GetLargestVisibleItem(ImageViewerItemPart.Item);

   // Show both in the label
   _label.Text = string.Format("First visible {0} - Largest {1}",
      firstVisible != null ? firstVisible.Text : "none",
      largest != null ? largest.Text : "none");
};

Target Platforms

Reference

ImageViewer Class
ImageViewer Members