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How to show thumbnail previews in RadGrid embedded in RadFileExplorer

HOW TO

This article describes the steps in order to show thumbnail previews inside the RadGrid embedded in RadFileExplorer control.

DESCRIPTION

The thumbnail images are shown in a custom column added to the Grid, embedded in RadFileExplorer. More detailed description about adding a custom columns can be found in this online demo.

SOLUTION

A custom FileBrowserContentProvider needs to be implemented in order to achieve the desired result. Only the behavior of the ResolveDirectory method needs to be changed and the easiest way to do this is to subclass the default provider (Telerik.Web.UI.Widgets.FileSystemContentProvider  and override that method only. In the overridden method, a HTML content (a <img> tag) needs to be added to the Attributes collection of the image files only:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using Telerik.Web.UI.Widgets;
using Telerik.Web.UI;
using System.IO;

namespace Telerik.Web.Examples.FileExplorer.CustomGridColumns
{
    public partial class Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                RadFileExplorer1.Configuration.ContentProviderTypeName = typeof(CustomColumnsContentProvider).AssemblyQualifiedName;

                string[] paths = new string[] { "~/Products" };
                RadFileExplorer1.Configuration.ViewPaths = paths;
                RadFileExplorer1.Configuration.UploadPaths = paths;
                RadFileExplorer1.Configuration.DeletePaths = paths;
            }
            AddThumbnailColumn();
        }

        private void AddGridColumn(string name, string uniqueName, bool sortable)
        {
            RemoveGridColumn(uniqueName);
            GridTemplateColumn gridTemplateColumn1 = new GridTemplateColumn();
            gridTemplateColumn1.HeaderText = name;
            if (sortable)
            {
                gridTemplateColumn1.SortExpression = uniqueName;
            }
            gridTemplateColumn1.UniqueName = uniqueName;
            gridTemplateColumn1.DataField = uniqueName;
            RadFileExplorer1.Grid.Columns.Add(gridTemplateColumn1);
        }
        private void RemoveGridColumn(string uniqueName)
        {
            if (!Object.Equals(RadFileExplorer1.Grid.Columns.FindByUniqueNameSafe(uniqueName), null))
            {
                RadFileExplorer1.Grid.Columns.Remove(RadFileExplorer1.Grid.Columns.FindByUniqueNameSafe(uniqueName));
            }
        }

        private void AddThumbnailColumn()
        {
            AddGridColumn("Thumb", "Thumb", false);
        }

        public class CustomColumnsContentProvider : Telerik.Web.UI.Widgets.FileSystemContentProvider
        {
            public CustomColumnsContentProvider(HttpContext context, string[] searchPatterns, string[] viewPaths, string[] uploadPaths, string[] deletePaths, string selectedUrl, string selectedItemTag)
                : base(context, searchPatterns, viewPaths, uploadPaths, deletePaths, selectedUrl, selectedItemTag)
            {
            }

            public override DirectoryItem ResolveDirectory(string path)
            {
                DirectoryItem oldItem = base.ResolveDirectory(path);
                foreach (FileItem fileItem in oldItem.Files)
                {
                    string[] imageExtensios = new string[] { ".jpg", ".gif", ".png" };// Images extensios

                    if (imageExtensios.Contains(fileItem.Extension))
                    {//Show thumbnails for images only
                        string pathToFile = fileItem.Location;
                        string htmlText = "<img src='" + pathToFile + "' alt='" + fileItem.Name + "' class='thumbImages'/>";
                        fileItem.Attributes.Add("Thumb", htmlText);
                    }
                }
                return oldItem;
            }
        }
    }
}


Please note that the attribute name (Thumb in the demo) should mach the UniqueName set to the added custom column.

The scr attribute of the image should be set to the FileItem's Location property. A CSS class named thumbImagesis applied to the added img element in order to control the appearance of the images. The CSS class needs to be placed on the page where the RadFileExplorer control is declared

   ## RESULT
thumbnails in RadGrid view

Note:
The designed behavior of RadGrid is to suppress the standard RadGrid events for the following HTML elements: input, textarea, label, img, select, option, button. This is to avoid interfering with the functionality of the standard elements. This implies that double-clicking on the thumbnail will not open the preview dialog. To enable this functionality you need to override the following RadGrid functions:

<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
    <script type="text/javascript">
        var origCanRiseRowEvent = Telerik.Web.UI.RadGrid.prototype._canRiseRowEvent;
        Telerik.Web.UI.RadGrid.prototype._canRiseRowEvent = function (e)
        {
            return origCanRiseRowEvent.apply(this, arguments) || Telerik.Web.UI.Grid.GetCurrentElement(e).tagName.toLowerCase() == "img";
        }

        var origShouldRaiseRowEvent = Telerik.Web.UI.GridSelection.prototype._shouldRaiseRowEvent;
        Telerik.Web.UI.GridSelection.prototype._shouldRaiseRowEvent = function (el)
        {
            return origShouldRaiseRowEvent.apply(this, arguments) || el.tagName.toLowerCase() == "img";
        }
    </script>
</telerik:RadCodeBlock>
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