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BeginUpdate Method

Summary

Prevents the control from drawing until the EndUpdate method is called.

Syntax

C++/CLI

C++

public void BeginUpdate()

public: 
void BeginUpdate();

public:  
   void BeginUpdate()

Remarks

The preferred way to add multiple items to a RasterImageList is to use the AddRange method of the RasterImageListItemCollection (accessed through the Items property of the RasterImageList). This enables you to add an array of items to the list in a single operation. However, if you want to add items one at a time using the Add method of the RasterImageListItemCollection class, you can use the BeginUpdate method to prevent the control from repainting the RasterImageList each time an item is added. Once you have completed the task of adding items to the control, call the EndUpdate method to enable the RasterImageList to repaint. This way of adding items can prevent flickered drawing of the RasterImageList when a large number of items are being added to the control.

Example

using Leadtools.WinForms; 
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
 
class MyForm2 : Form 
{ 
   RasterImageViewer viewer; 
   RasterImageList imageList; 
   RasterCodecs codecs; 
 
   public MyForm2() 
   { 
      // Set the size of the form 
      Size = new Size(400, 200); 
 
      // Create a new RasterImageList control 
      imageList = new RasterImageList(); 
      imageList.Dock = DockStyle.Left; 
      imageList.SelectionMode = RasterImageListSelectionMode.Single; 
      Controls.Add(imageList); 
      imageList.BringToFront(); 
 
      // Add a handler to the SelectedIndexChanged event 
      imageList.SelectedIndexChanged += new EventHandler(rasterImageList_SelectedIndexChanged); 
 
      Splitter splitter = new Splitter(); 
      splitter.Dock = DockStyle.Left; 
      Controls.Add(splitter); 
      splitter.BringToFront(); 
 
      viewer = new RasterImageViewer(); 
      viewer.Dock = DockStyle.Fill; 
      Controls.Add(viewer); 
      viewer.BringToFront(); 
 
      // Now load all our images 
      codecs = new RasterCodecs(); 
 
      string folderName = LEAD_VARS.ImagesDir; 
      string[] files = Directory.GetFiles(folderName, "*.*"); 
 
      // This is going to be a lengthy operation 
      // Suspend painting the RasterImageList 
      imageList.BeginUpdate(); 
 
      foreach (string fileName in files) 
      { 
         // Load the image as a thumbnail 
         RasterImage image = LoadThumbnail(fileName); 
 
         // Only add an item if we loaded the image successfuly 
         if (image != null) 
         { 
            // Create an item 
            RasterImageListItem item = new RasterImageListItem(); 
 
 
            // Setup the item information 
            item.Image = image; 
            item.Text = Path.GetFileName(fileName); 
            item.Page = 1; 
 
            // To load this image in original size later 
            item.FileName = fileName; 
 
            // Add the item into RasterImageList 
            imageList.Items.Add(item); 
         } 
      } 
 
      imageList.EndUpdate(); 
 
   } 
 
   private void rasterImageList_SelectedIndexChanged(object sender, EventArgs e) 
   { 
      // User has selected an item from the RasterImageList control. 
      // Re-load the item image and show it in original size in the viewer 
 
      // Get the selected item(s) 
      RasterImageListItemCollection selectedItems = imageList.SelectedItems; 
      if (selectedItems != null && selectedItems.Count == 1) 
      { 
         RasterImageListItem item = selectedItems[0]; 
 
         // Load the image in its original size and set it in the viewer 
         viewer.Image = codecs.Load( 
            item.FileName, 
            0, 
            CodecsLoadByteOrder.BgrOrGray, 
            1, 
            1); 
      } 
   } 
 
   private RasterImage LoadThumbnail(string fileName) 
   { 
      RasterImage image = null; 
 
      try 
      { 
         // See if we can load this image 
         CodecsImageInfo info = codecs.GetInformation(fileName, false, 1); 
 
         if (info.Format != RasterImageFormat.Unknown) 
         { 
            // Yes, calculate the thumbnail size to fit into RasterImageList.ItemImageSize 
            Rectangle rc = new Rectangle( 
               0, 
               0, 
               imageList.ItemImageSize.Width, 
               imageList.ItemImageSize.Height); 
 
            rc = RasterImageList.GetFixedAspectRatioImageRectangle(info.Width, info.Height, rc); 
 
            // Load the thumbnail 
            image = codecs.Load( 
               fileName, 
               rc.Width, 
               rc.Height, 
               24, 
               RasterSizeFlags.Resample, 
               CodecsLoadByteOrder.BgrOrGray, 
               1, 
               1); 
         } 
         else 
            image = null; 
      } 
      catch 
      { 
         image = null; 
      } 
      return image; 
   } 
} 
 
public void RasterImageList_Image() 
{ 
   MyForm2 form = new MyForm2(); 
   form.ShowDialog(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
}

Requirements

Target Platforms