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RasterThumbnailBrowser Class
See Also  Members   Example 
Leadtools.WinForms Namespace : RasterThumbnailBrowser Class




Derives from the RasterImageList control to provides functionality to automatically generate thumbnails for images in a disk folder.

Object Model



Syntax

Visual Basic (Declaration) 
<ToolboxBitmapAttribute()>
<DefaultEventAttribute("SelectedIndexChanged")>
<DefaultPropertyAttribute("ViewStyle")>
Public Class RasterThumbnailBrowser 
   Inherits RasterImageList
Visual Basic (Usage)Copy Code
Dim instance As RasterThumbnailBrowser
C# 
[ToolboxBitmapAttribute()]
[DefaultEventAttribute("SelectedIndexChanged")]
[DefaultPropertyAttribute("ViewStyle")]
public class RasterThumbnailBrowser : RasterImageList
Managed Extensions for C++ 
[ToolboxBitmapAttribute()]
[DefaultEventAttribute("SelectedIndexChanged")]
[DefaultPropertyAttribute("ViewStyle")]
public __gc class RasterThumbnailBrowser : public RasterImageList
C++/CLI 
[ToolboxBitmapAttribute()]
[DefaultEventAttribute("SelectedIndexChanged")]
[DefaultPropertyAttribute("ViewStyle")]
public ref class RasterThumbnailBrowser : public RasterImageList

Example

This example creates an instance of a RasterThumbnailBrowser control and adds it to a form Next it displays thumbnail images of all images in a directory

Visual BasicCopy Code
Private Class MyForm : Inherits Form
   Public theBrowser As RasterThumbnailBrowser
   Public cancelOperation As Boolean ' Informs us if the user canceled the operation
   Public buttonCancel As Button ' Cancel browse loading
   Public buttonBrowse As Button ' Diplays the browse control
   Public progressBar As ProgressBar ' shows progress of loading browse images
   Private Sub buttonBrowse_Click(ByVal sender As Object, ByVal e As EventArgs)
      ' If we are already loading thumbails, cancel
      ' this operation
      If theBrowser.IsLoadingThumbnails Then
         theBrowser.CancelLoadingThumbnails()
      End If

      ' Clean all the items
      theBrowser.Items.Clear()

      ' Update the application state
      buttonCancel.Enabled = True
      progressBar.Value = 0

      ' And load the new thumbnails
      cancelOperation = False

      Dim folderPath As String = "C:\program files\LEAD Technologies\LEADTOOLS 15\Images"
      theBrowser.LoadThumbnails(folderPath, "*.*", RasterThumbnailBrowserLoadFlags.Block)
   End Sub

   Private Sub thumbnailBrowser_LoadThumbnail(ByVal sender As Object, ByVal e As RasterThumbnailBrowserLoadThumbnailEventArgs)
      ' If this is the first iteration, update the progress bar minimum and maximum values
      If e.Index = 0 Then
         progressBar.Minimum = 0
         progressBar.Maximum = e.Total - 1
      End If

      ' Update where we are in the loading operation
      progressBar.Value = e.Index

      ' Check if we need to cancel (due to the user clicking the Cancel button)
      If cancelOperation Then
         e.Cancel = True
      End If
   End Sub

   Private Sub thumbnailBrowser_AddFile(ByVal sender As Object, ByVal e As RasterThumbnailBrowserAddFileEventArgs)
      Console.WriteLine("AddFile: {0} Add: {1}", e.FileName, e.Add)
   End Sub

   Private Sub thumbnailBrowser_FinishedLoadingThumbnails(ByVal sender As Object, ByVal e As EventArgs)
      buttonCancel.Enabled = False
   End Sub

   Private Sub buttonCancel_Click(ByVal sender As Object, ByVal e As EventArgs)
      ' The user has clicked the cancel button
      Me.cancelOperation = True
   End Sub

   ' Create custom images to use as the "error" and "loading" thumbnails.
   Private Sub CreateErrorThumbnail()
      ' Get the image size
      Dim imageSize As Size = theBrowser.ItemImageSize

      ' No "loading" thumbnail
      theBrowser.LoadingThumbnail = Nothing

      ' For the "error" thumbnail, create a red X image
      Dim palette As RasterColor() = New RasterColor() {}
      Dim image As RasterImage = New RasterImage(RasterMemoryFlags.Conventional, imageSize.Width, imageSize.Height, 24, RasterByteOrder.Bgr, RasterViewPerspective.TopLeft, palette, IntPtr.Zero, 0)

      Dim hdc As IntPtr = image.CreateLeadDC()
      Dim g As Graphics = Graphics.FromHdc(hdc)

      g.FillRectangle(Brushes.Magenta, 0, 0, imageSize.Width, imageSize.Height)

      g.DrawLine(Pens.Red, 0, 0, imageSize.Width, imageSize.Height)
      g.DrawLine(Pens.Red, imageSize.Width, 0, 0, imageSize.Height)

      g.Dispose()
      RasterImage.DeleteLeadDC(hdc)

      ' Make this image transparent
      image.Transparent = True
      image.TransparentColor = RasterColor.FromGdiPlusColor(Color.Magenta)

      theBrowser.ErrorThumbnail = image
   End Sub

   Public Sub Cleanup()
      RemoveHandler buttonBrowse.Click, AddressOf buttonBrowse_Click
      RemoveHandler buttonCancel.Click, AddressOf buttonCancel_Click
      RemoveHandler theBrowser.LoadThumbnail, AddressOf thumbnailBrowser_LoadThumbnail
      RemoveHandler theBrowser.FinishedLoadingThumbnails, AddressOf thumbnailBrowser_FinishedLoadingThumbnails
   End Sub

   Public Sub New()
      Size = New Size(300, 200)

      ' create the browser
      theBrowser = New RasterThumbnailBrowser()
      theBrowser.Codecs = New RasterCodecs()
      theBrowser.Dock = DockStyle.Fill
      theBrowser.ItemSpacingSize = New Size(10, 10)
      theBrowser.ThumbnailSizeFlags = RasterSizeFlags.Bicubic
      AddHandler theBrowser.LoadThumbnail, AddressOf thumbnailBrowser_LoadThumbnail
      AddHandler theBrowser.FinishedLoadingThumbnails, AddressOf thumbnailBrowser_FinishedLoadingThumbnails
      AddHandler theBrowser.AddFile, AddressOf thumbnailBrowser_AddFile

      ' Create a thumbnail image to be displayed on error
      CreateErrorThumbnail()

      ' add a panel
      Dim panel As Panel = New Panel()
      panel.Dock = DockStyle.Left
      panel.Width = 100
      Controls.Add(panel)
      panel.BringToFront()

      ' add a "browse" button
      buttonBrowse = New Button()
      buttonBrowse.Text = "Browse"
      buttonBrowse.Dock = DockStyle.Top
      panel.Controls.Add(buttonBrowse)
      AddHandler buttonBrowse.Click, AddressOf buttonBrowse_Click

      ' add a "cancel" button
      buttonCancel = New Button()
      buttonCancel.Text = "Cancel"
      buttonBrowse.Dock = DockStyle.Bottom
      panel.Controls.Add(buttonCancel)
      AddHandler buttonCancel.Click, AddressOf buttonCancel_Click

      ' add a progress bar
      progressBar = New ProgressBar()
      progressBar.Dock = DockStyle.Bottom
      Controls.Add(progressBar)

      Controls.Add(theBrowser)
      theBrowser.BringToFront()
   End Sub

   Private Sub InitializeComponent()
      Me.SuspendLayout()
      '
      ' MyForm
      '
      Me.ClientSize = New System.Drawing.Size(315, 273)
      Me.Name = "MyForm"
      Me.ResumeLayout(False)

   End Sub
End Class
Public Sub RasterThumbnailBrowser_RasterThumbnailBrowser()
   RasterCodecs.Startup()
   Dim form As MyForm = New MyForm()
   form.ShowDialog()
   form.Cleanup()
   RasterCodecs.Shutdown()
End Sub
C#Copy Code
class MyForm : Form 
{ 
   public RasterThumbnailBrowser theBrowser; 
   public bool cancelOperation;        // Informs us if the user canceled the operation 
   public Button buttonCancel;         // Cancel browse loading 
   public Button buttonBrowse;         // Diplays the browse control 
   public ProgressBar progressBar;     // shows progress of loading browse images 
   void buttonBrowse_Click(object sender, EventArgs e) 
   { 
      // If we are already loading thumbails, cancel 
      // this operation 
      if(theBrowser.IsLoadingThumbnails) 
         theBrowser.CancelLoadingThumbnails(); 
 
      // Clean all the items 
      theBrowser.Items.Clear(); 
 
      // Update the application state 
      buttonCancel.Enabled = true; 
      progressBar.Value = 0; 
 
      // And load the new thumbnails 
      cancelOperation = false; 
 
      string folderPath = @"C:\program files\LEAD Technologies\LEADTOOLS 15\Images"; 
      theBrowser.LoadThumbnails(folderPath, "*.*", RasterThumbnailBrowserLoadFlags.Block); 
   } 
 
   private void thumbnailBrowser_LoadThumbnail(object sender, RasterThumbnailBrowserLoadThumbnailEventArgs e) 
   { 
      // If this is the first iteration, update the progress bar minimum and maximum values 
      if(e.Index == 0) 
      { 
         progressBar.Minimum = 0; 
         progressBar.Maximum = e.Total - 1; 
      } 
 
      // Update where we are in the loading operation 
      progressBar.Value = e.Index; 
 
      // Check if we need to cancel (due to the user clicking the Cancel button) 
      if(cancelOperation) 
         e.Cancel = true; 
   } 
 
   private void thumbnailBrowser_AddFile(object sender, RasterThumbnailBrowserAddFileEventArgs e) 
   { 
      Console.WriteLine("AddFile: {0}    Add: {1}", e.FileName, e.Add); 
   } 
 
   private void thumbnailBrowser_FinishedLoadingThumbnails(object sender, EventArgs e) 
   { 
      buttonCancel.Enabled = false; 
   } 
 
   private void buttonCancel_Click(object sender, EventArgs e) 
   { 
      // The user has clicked the cancel button 
      this.cancelOperation = true; 
   } 
 
   // Create  custom images to use as the "error" and "loading" thumbnails. 
   void CreateErrorThumbnail() 
   { 
      // Get the image size 
      Size imageSize = theBrowser.ItemImageSize; 
 
      // No "loading" thumbnail 
      theBrowser.LoadingThumbnail = null; 
 
      // For the "error" thumbnail, create a red X image 
      RasterColor[] palette = new RasterColor[0]; 
      RasterImage image = new RasterImage( 
         RasterMemoryFlags.Conventional, 
         imageSize.Width, 
         imageSize.Height, 
         24, 
         RasterByteOrder.Bgr, 
         RasterViewPerspective.TopLeft, 
      palette, 
      IntPtr.Zero, 
      0 
      ); 
 
      IntPtr hdc = image.CreateLeadDC(); 
      Graphics g = Graphics.FromHdc(hdc); 
 
      g.FillRectangle(Brushes.Magenta, 0, 0, imageSize.Width, imageSize.Height); 
 
      g.DrawLine(Pens.Red, 0, 0, imageSize.Width, imageSize.Height); 
      g.DrawLine(Pens.Red, imageSize.Width, 0, 0, imageSize.Height); 
 
      g.Dispose(); 
      RasterImage.DeleteLeadDC(hdc); 
 
      // Make this image transparent 
      image.Transparent = true; 
      image.TransparentColor = RasterColor.FromGdiPlusColor(Color.Magenta); 
 
      theBrowser.ErrorThumbnail = image; 
   } 
 
   public void Cleanup() 
   { 
      buttonBrowse.Click -= new EventHandler(buttonBrowse_Click); 
      buttonCancel.Click -= new EventHandler(buttonCancel_Click); 
      theBrowser.LoadThumbnail -= new EventHandler<RasterThumbnailBrowserLoadThumbnailEventArgs>(thumbnailBrowser_LoadThumbnail); 
      theBrowser.FinishedLoadingThumbnails -= new EventHandler(thumbnailBrowser_FinishedLoadingThumbnails); 
   } 
 
   public MyForm() 
   { 
      Size = new Size(300, 200); 
 
      // create the browser 
      theBrowser = new RasterThumbnailBrowser(); 
      theBrowser.Codecs = new RasterCodecs(); 
      theBrowser.Dock = DockStyle.Fill; 
      theBrowser.ItemSpacingSize = new Size(10, 10); 
      theBrowser.ThumbnailSizeFlags = RasterSizeFlags.Bicubic; 
      theBrowser.LoadThumbnail += new EventHandler<RasterThumbnailBrowserLoadThumbnailEventArgs>(thumbnailBrowser_LoadThumbnail); 
      theBrowser.FinishedLoadingThumbnails += new EventHandler(thumbnailBrowser_FinishedLoadingThumbnails); 
      theBrowser.AddFile += new EventHandler<RasterThumbnailBrowserAddFileEventArgs>(thumbnailBrowser_AddFile); 
 
      // Create a thumbnail image to be displayed on error 
      CreateErrorThumbnail(); 
 
      // add a panel 
      Panel panel = new Panel(); 
      panel.Dock = DockStyle.Left; 
      panel.Width = 100; 
      Controls.Add(panel); 
      panel.BringToFront(); 
 
      // add a "browse" button 
      buttonBrowse = new Button(); 
      buttonBrowse.Text = "Browse"; 
      buttonBrowse.Dock = DockStyle.Top; 
      panel.Controls.Add(buttonBrowse); 
      buttonBrowse.Click += new EventHandler(buttonBrowse_Click); 
 
      // add a "cancel" button 
      buttonCancel = new Button(); 
      buttonCancel.Text = "Cancel"; 
      buttonBrowse.Dock = DockStyle.Bottom; 
      panel.Controls.Add(buttonCancel); 
      buttonCancel.Click += new EventHandler(buttonCancel_Click); 
 
      // add a progress bar 
      progressBar = new ProgressBar(); 
      progressBar.Dock = DockStyle.Bottom; 
      Controls.Add(progressBar); 
 
      Controls.Add(theBrowser); 
      theBrowser.BringToFront(); 
   } 
 
   private void InitializeComponent() 
   { 
      this.SuspendLayout(); 
      //  
      // MyForm 
      //  
      this.ClientSize = new System.Drawing.Size(315, 273); 
      this.Name = "MyForm"; 
      this.ResumeLayout(false); 
 
   } 
}  
public void RasterThumbnailBrowser_RasterThumbnailBrowser() 
{ 
   RasterCodecs.Startup(); 
   MyForm form = new MyForm(); 
   form.ShowDialog(); 
   form.Cleanup(); 
   RasterCodecs.Shutdown(); 
}

Remarks

The RasterThumbnailBrowser lets you quickly and easily create thumbnails for images that reside on any file folder in the system. Since the RasterThumbnailBrowser derives from the RasterImageList control, you get all the visual styles available to the image list (different view styles, control the item size, color, etc.) as well as the same interface to manually add/remove/edit items.

You call the LoadThumbnails method passing it the path of the folder for which you want to create thumbnails, a search pattern and a boolean value indicating whether you want the control to block until all thumbnails are created or to return immediately and continue loading the thumbnails in a background thread.

The control will first read the folder and create the items you need. These items will initially have a default "loading" thumbnail set in their RasterImageListItem.Image that you can access and change through the LoadingThumbnail property. Once the item image file is loaded and its thumbnail extracted, the control will replace the item Image property with the correct thumbnail. This gives the user a visual feedback on which items are loaded and which are yet to be loaded. If the control cannot load a certain file (for example, if the file is not a valid image format file), an "error" thumbnail will be used in the item. You can access and change this thumbnail image through the ErrorThumbnail property.

During the loading operation, you can check the IsLoadingThumbnails property to determine if the control is still loading thumbnails in the background. The FinishedLoadingThumbnails event will fire when the loading operation is done. You can subscribe to the LoadThumbnail event to get feedback about the item currently being loaded. You use this event also to update a progress bar on your application and to cancel the load process if neeeded. The CancelLoadingThumbnails method lets you cancel the load operation at any time.

The ThumbnailSizeFlags property lets you control the quality of the thumbnail images created by the RasterThumbnailBrowser control.

Inheritance Hierarchy

System.Object
   System.MarshalByRefObject
      System.ComponentModel.Component
         System.Windows.Forms.Control
            Leadtools.WinForms.RasterImageList
               Leadtools.WinForms.RasterThumbnailBrowser

Requirements

Target Platforms: Microsoft .NET Framework 2.0, Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also