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TransformChanged Event


Occurs when the transformation matrix of the view or any of the item changes.

public event EventHandler TransformChanged 
   event EventHandler^ TransformChanged 

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.


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:

using Leadtools; 
using Leadtools.Controls; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
public ImageViewerForm _form = new ImageViewerForm(); 
public ImageViewer _imageViewer; 
public void ImageViewerTransformChangedExample() 
   // Get the ImageViewer control from the Form 
   _imageViewer = _form.ImageViewer; 
   // Clear all the images already the viewer 
   // 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(400, 400); 
   _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(LEAD_VARS.ImagesDir, string.Format("ocr{0}.tif", page)); 
         // Create a thumbnail from the image 
         using (var image = codecs.Load(fileName, page)) 
            item.Image = image.CreateThumbnail(380, 380, 24, RasterViewPerspective.TopLeft, RasterSizeFlags.Resample); 
         item.Text = string.Format("Item {0}", page - 1); 
   // 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 Debug Console 
      Debug.WriteLine(string.Format("First visible {0} - Largest {1}", 
         firstVisible != null ? firstVisible.Text : "none", 
         largest != null ? largest.Text : "none")); 
static class LEAD_VARS 
   public const string ImagesDir = @"C:\LEADTOOLS23\Resources\Images"; 
Event Data
senderobjectThe source of the event.

Target Platforms

Help Version 23.0.2024.2.29
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Leadtools.Controls Assembly

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© 1991-2023 LEAD Technologies, Inc. All Rights Reserved.