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RasterThumbnailBrowser Class

Summary

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

Syntax

C#
VB
C++
[DefaultPropertyAttribute("ViewStyle")] 
[DefaultEventAttribute("SelectedIndexChanged")] 
public class RasterThumbnailBrowser : RasterImageList 
  
<ToolboxBitmapAttribute()> 
<DefaultEventAttribute("SelectedIndexChanged")> 
<DefaultPropertyAttribute("ViewStyle")> 
Public Class RasterThumbnailBrowser  
   Inherits Leadtools.Winforms.RasterImageList 
   Implements System.ComponentModel.IComponent, System.ComponentModel.ISynchronizeInvoke, System.IDisposable, System.Windows.Forms.IBindableComponent, System.Windows.Forms.IDropTarget, System.Windows.Forms.IWin32Window  
[ToolboxBitmapAttribute()] 
[DefaultEventAttribute("SelectedIndexChanged")] 
[DefaultPropertyAttribute("ViewStyle")] 
public ref class RasterThumbnailBrowser : public Leadtools.Winforms.RasterImageList, System.ComponentModel.IComponent, System.ComponentModel.ISynchronizeInvoke, System.IDisposable, System.Windows.Forms.IBindableComponent, System.Windows.Forms.IDropTarget, System.Windows.Forms.IWin32Window   

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(string,string,rasterthumbnailbrowserloadflags) 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 needed. 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.

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

C#
VB
using Leadtools.WinForms; 
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
 
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 = LEAD_VARS.ImagesDir; 
      theBrowser.LoadStamp = true; 
      theBrowser.LoadThumbnails(folderPath, "*.*", RasterThumbnailBrowserLoadFlags.Block); 
 
      theBrowser.Refresh(); 
 
      theBrowser.EnableBrowserWatcher = true; 
   } 
 
   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 = RasterImagePainter.CreateLeadDC(image); 
      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(); 
      RasterImagePainter.DeleteLeadDC(hdc); 
 
      // Make this image transparent 
      image.Transparent = true; 
      image.TransparentColor = RasterColor.FromKnownColor(RasterKnownColor.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() 
{ 
   MyForm form = new MyForm(); 
   form.ShowDialog(); 
   form.Cleanup(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
} 
Imports Leadtools.WinForms 
Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.Drawing 
 
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 = LEAD_VARS.ImagesDir 
      theBrowser.LoadStamp = True 
      theBrowser.LoadThumbnails(folderPath, "*.*", RasterThumbnailBrowserLoadFlags.Block) 
 
      theBrowser.Refresh() 
 
      theBrowser.EnableBrowserWatcher = True 
   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 = RasterImagePainter.CreateLeadDC(image) 
      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() 
      RasterImagePainter.DeleteLeadDC(hdc) 
 
      ' Make this image transparent 
      image.Transparent = True 
      image.TransparentColor = RasterColor.FromKnownColor(RasterKnownColor.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_LoadThumbnails2() 
   Dim form As MyForm = New MyForm() 
   form.ShowDialog() 
   form.Cleanup() 
End Sub 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class 

Requirements

Target Platforms

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Leadtools.WinForms Assembly