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TransformChanged Event (ImageViewer)

Summary

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

Syntax

C++

public event EventHandler TransformChanged

Public Event TransformChanged As EventHandler

public:  
   event EventHandler^ TransformChanged

Remarks

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.

Example

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 LeadtoolsExamples.Common; 
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"); 
};

Imports Leadtools 
Imports Leadtools.Controls 
Imports Leadtools.Codecs 
Imports Leadtools.Drawing 
Imports Leadtools.ImageProcessing 
Imports Leadtools.ImageProcessing.Color 
Imports LeadtoolsControlsExamples.LeadtoolsExamples.Common 
 
' 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