Adding a thumbnail view & navigation to the PdfViewer control

If you’ve used the PdfViewer control you’ll know that it provides an easy way to display PDF documents within  your WinForms application. Currently, you can select text, manipulate a file (via the PdfDocumentProccessor non-visual component) and even fill out PDF forms. The 14.2.5 release even allows the ability to programmatically fill in PDF forms–pretty useful stuff for those of you processing electronic documents and working towards the dream of a paperless office.

One feature that I find lacking in the PdfViewer control is a good thumbnail navigation system. Adobe Reader offers this ability with a simple thumbnail navigation system; each page of the document is displayed as a small image which users can quickly scroll through. Double-clicking on a thumbnail opens the corresponding page and end users can even change the size of the thumbnail images.

Screenshot of Adobe Reader's thumbnail navigation
Screenshot of Adobe Reader’s thumbnail navigation

The DevExpress PdfViewer will display thumbnails for pages if you zoom out to about the 10-20% zoom level, but the functionality ends there. You can’t double-click one of the pages and have the viewer navigate to that particular page. How can we implement a system similar to Adobe Reader ourselves?

DevExpress's non-functional thumbnail mode.
DevExpress’s non-functional thumbnail mode.

To mimic Adobe Reader’s thumbnail function, I immediately though of a few controls that might make our job easier:

  • GalleryControl – This could easily organize and display our thumbnail images. We don’t really need any grouping functionality but that’s easy to ignore.
  • GridControl – This tends to be my default go-to for displaying a list of items/records. But that’s only the first half of the equation–after that, we’d have to decide which view type to use. The LayoutView in a single column mode would work well, but honestly, I hate the layout editor.

In the end, I decided to use the GridControl, but with the WinExplorerView instead of the LayoutView. The WinExplorerView mimics the various ways you might view a folder in Windows Explorer–details, large icons, small icons etc… This is all controlled via the OptionsViewStyles property, so we can even allow the user to toggle between styles at runtime.

At the end of this exercise, we’ll end up with something like this:

Our semi-finished product: a PdfViewer control with a sidebar of page thumbnails.
Our semi-finished product: a PdfViewer control with a sidebar of page thumbnails.

To being, we’ll create a form and place a LayoutControl onto the form. Dock the LayoutControl to fill the form, and then drop a GridControl onto the LayoutControl, followed by a PdfViewer control to the right. The GridControl can be placed in a LayoutControlGroup and the PdfViewer can just be contained within a standard LayoutControlItem. I also changed the view type of the GridControl from the default GridView to the WinExplorerView type.

The thumbnail logic is all going to be contained within a class I’ve called PdfPage. Let’s have a look at it:

namespace PdfThumbnails
{
    /// <summary>
    /// Encapsulates the properties and methods of a PdfPage
    /// </summary>
    sealed public class PdfPage
    {

        #region Public properties

        /// <summary>
        /// Gets or sets the number of this Pdf Page
        /// </summary>
        public int PageNumber
        {
            get;
            set;
        }

        /// <summary>
        /// Gets the thumbnail image for this Pdf Page
        /// </summary>
        public Image Thumbnail
        {
            get;
            private set;
        }

        #endregion


        /// <summary>
        /// Initializes a new instance of the PdfPage class
        /// </summary>
        public PdfPage()
        {

        }



        /// <summary>
        /// Sets the thumbnail image for the current PdfPage
        /// </summary>
        /// <param name="DocumentViewer">PdfViewer control responsible for displaying the PdfPage</param>
        public void SetThumbnailImage(PdfViewer DocumentViewer)
        {
            int PageWidth = 0;
            int PageHeight = 0;
            int PagePixelWidth = 0;
            int PagePixelHeight = 0;

            using (Graphics graphics = DocumentViewer.CreateGraphics())
            {
                //Get the page dimensions
                PageWidth = (int)DocumentViewer.GetPageSize(PageNumber).Width;
                PageHeight = (int)DocumentViewer.GetPageSize(PageNumber).Height;

                //Convert the page dimensions into screen pixels
                PagePixelWidth = (PageWidth * (int)graphics.DpiX);
                PagePixelHeight = (PageHeight * (int)graphics.DpiY);

                Thumbnail = DocumentViewer.CreateBitmap(PageNumber, Math.Max(PagePixelWidth, PagePixelHeight));

            }   //End the using() statement

        }   //End the SetThumbnailImage class



    }   //End the PdfPage class
}   //End the PdfThumbnails namespace

The class is pretty sparse in and of itself–just two properties. One to keep track of the page number within the document and another to hold the thumbnail image. The important part is the SetThumbnailImage method, which is in charge of creating a thumbnail for this page.

The method requires an instance of the PdfViewer control because unfortunately, the control doesn’t offer a way to get an instance of a single visual page. Luckily, having an instance of the PdfViewer control allows to use its CreateGraphics method to get a reference to the drawing surface which will be useful for generating that thumbnail. And it is useful because the PdfViewer’s GetPageSize method returns the page’s dimensions in inches, not in pixels.

I think this was a poor decision on the part of DevExpress, because it’s not mentioned in the documentation that SizeF struct returned from the method is measured in inches and I have no clue how useful that information would be in metric-based countries. Our demonstration PDF will return 8 & 11 for the page’s width and height, respectively. Since we don’t want to create an 8px X 11px Bitmap, we need to convert these dimensions into pixels.

I’m not a graphics programmer, but I do know that DPI settings will influence the conversion between inches and pixels–after all, its name implies how many dots-per-inch there are on our display! Because of this, we can’t just multiply the page dimensions by some magic number. We have to take this DPI into account and multiply by that instead.

Once we have the page and screen dimensions, it’s a matter of using the PdfViewer’s CreateBitmap method to generate a Bitmap image of current page.

I then create a BindingSource component on the Form and set its DataSource property the PdfThumb class. After that, I set the GridControl’s DataSource to this BindingSource component. The GridControl will automatically read the scheme from this data source, but because we’re using the GridControl with a WinExplorerView there aren’t any columns. Instead, there’s a ColumnSet, which maps properties of the data source to the predefined properties of the WinExplorerView.

Since a future version of this application may allow a user to toggle between thumbnail sizes, we’ll set the values for SmallImageColumn, MediumImageColumnn, LargeImageColumn and ExtraLargeImageColumn members of that ColumnSet property. These are all set to the PdfPage’s ThumbnailImage property, and we’ll set the ColumnSet’s Description andTextColumn properties to the PageNumber property.

At this point, we have a PdfViewer control capable of displaying our PDF, a GridControl capable of displaying page thumbnails and a class capable of generating those thumbnails. The only thing we need to do is actually tell our application to generate those thumbnails at runtime when a PDF is loaded into the viewer.

Create a handler for the the PdfViewer’s DocumentChanged event as this will be fired every time a document is loaded into the PdfViewer control. After that, it’s just a matter of looping through the pages of the PdfViewer and creating an instance of the PdfPage class for each:

/// <summary>
/// Document changed event handler for the PdfViewer control
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void pdfViewer1_DocumentChanged(object sender, DevExpress.XtraPdfViewer.PdfDocumentChangedEventArgs e)
{
    IList<PdfPage> documentPages = new List<PdfPage>(pdfViewer1.PageCount);

    for (int i = 1; i <= pdfViewer1.PageCount; i++)
    {
        PdfPage documentPage = new PdfPage();
        documentPage.PageNumber = i;
        documentPage.SetThumbnailImage(pdfViewer1);

        documentPages.Add(documentPage);

    }   //End the for() loop

    bindingSource1.DataSource = documentPages;

}   //End the pdfViewer1_DocumentChanged() method

Once that’s done, our GridControl will automatically show those page thumbnails when the application is run and a Pdf is loaded into the viewer.

The final step is to handle the WinExplorerView’s DoubleClick event:

/// <summary>
/// Double click event handler for the Thumbnails WinExplorerView
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void wvThumbnails_DoubleClick(object sender, EventArgs e)
{
    PdfPage currentPage = (wvThumbnails.GetFocusedRow() as PdfPage);

    pdfViewer1.CurrentPageNumber = currentPage.PageNumber;

}   //End the wvThumbnails_DoubleClick() method

This code simply takes the current row (thumbnail) from the thumbnail grid and casts it to an instance of our PdfPage class. Since the class is nice enough to keep track of its page number on our behalf, we can tell the PdfViewer to navigate to corresponding page.

And that’s all there is to it! Once small class, a couple of event handlers and we’re done. In an upcoming post, we’ll look at adding a few additional features to this application such as:

  • Allowing the user to change the thumbnail size
  • Synchronizing the thumbnail sidebar scroll position to the PdfViewer scroll position
  • Showing a magnified image of the thumbnail when the user hovers over a thumbnail image

And don’t worry, we’ll also get back to the DxContactList Xpo tutorial soon! In the meantime, here is the full source code for this tutorial: PdfThumbnails.

Adding a thumbnail view & navigation to the PdfViewer control