Question

I am using the WebBrowser control inside a Windows Form to display a PDF.

Whenever the PDF is regenerated, however, the WebBrowser control only displays its local cached version and not the updated version from the server.

I am using the Refresh() method shown below to try and force the control to reload the PDF, but it doesn’t work:

_webBrowser.Navigate(pdfUrl);

_webBrowser.Refresh(WebBrowserRefreshOption.Completely)

Do I have to do anything else to force the refresh to reload the PDF from the server?

Answer 1

Sheng Jiang is correct – you need the programmatically clear IE’s cache. Here is sample code showing how to do this in c#:
http://www.gutgames.com/post/Clearing-the-Cache-of-a-WebBrowser-Control.aspx

Copy in case the page goes offline:

/**
* Modified from code originally found here: 
http://support.microsoft.com/kb/326201
**/

#region Usings
using System;
using System.Runtime.InteropServices;

#endregion

namespace Utilities.Web.WebBrowserHelper
{
    /// <summary>
    /// Class for clearing the cache
    /// </summary>
    public static class WebBrowserHelper
    {
        #region Definitions/DLL Imports
        /// <summary>
        /// For PInvoke: Contains information about an entry in the Internet cache
        /// </summary>
        [StructLayout(LayoutKind.Explicit, Size = 80)]
        public struct INTERNET_CACHE_ENTRY_INFOA
        {
            [FieldOffset(0)]
            public uint dwStructSize;
            [FieldOffset(4)]
            public IntPtr lpszSourceUrlName;
            [FieldOffset(8)]
            public IntPtr lpszLocalFileName;
            [FieldOffset(12)]
            public uint CacheEntryType;
            [FieldOffset(16)]
            public uint dwUseCount;
            [FieldOffset(20)]
            public uint dwHitRate;
            [FieldOffset(24)]
            public uint dwSizeLow;
            [FieldOffset(28)]
            public uint dwSizeHigh;
            [FieldOffset(32)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastModifiedTime;
            [FieldOffset(40)]
            public System.Runtime.InteropServices.ComTypes.FILETIME ExpireTime;
            [FieldOffset(48)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastAccessTime;
            [FieldOffset(56)]
            public System.Runtime.InteropServices.ComTypes.FILETIME LastSyncTime;
            [FieldOffset(64)]
            public IntPtr lpHeaderInfo;
            [FieldOffset(68)]
            public uint dwHeaderInfoSize;
            [FieldOffset(72)]
            public IntPtr lpszFileExtension;
            [FieldOffset(76)]
            public uint dwReserved;
            [FieldOffset(76)]
            public uint dwExemptDelta;
        }

        // For PInvoke: Initiates the enumeration of the cache groups in the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheGroup(
        int dwFlags,
        int dwFilter,
        IntPtr lpSearchCondition,
        int dwSearchCondition,
        ref long lpGroupId,
        IntPtr lpReserved);

        // For PInvoke: Retrieves the next cache group in a cache group enumeration
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheGroup(
        IntPtr hFind,
        ref long lpGroupId,
        IntPtr lpReserved);

        // For PInvoke: Releases the specified GROUPID and any associated state in the cache index file
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheGroup",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheGroup(
        long GroupId,
        int dwFlags,
        IntPtr lpReserved);

        // For PInvoke: Begins the enumeration of the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindFirstUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr FindFirstUrlCacheEntry(
        [MarshalAs(UnmanagedType.LPTStr)] string lpszUrlSearchPattern,
        IntPtr lpFirstCacheEntryInfo,
        ref int lpdwFirstCacheEntryInfoBufferSize);

        // For PInvoke: Retrieves the next entry in the Internet cache
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "FindNextUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool FindNextUrlCacheEntry(
        IntPtr hFind,
        IntPtr lpNextCacheEntryInfo,
        ref int lpdwNextCacheEntryInfoBufferSize);

        // For PInvoke: Removes the file that is associated with the source name from the cache, if the file exists
        [DllImport(@"wininet",
        SetLastError = true,
        CharSet = CharSet.Auto,
        EntryPoint = "DeleteUrlCacheEntryA",
        CallingConvention = CallingConvention.StdCall)]
        public static extern bool DeleteUrlCacheEntry(
        IntPtr lpszUrlName);
        #endregion

        #region Public Static Functions

        /// <summary>
        /// Clears the cache of the web browser
        /// </summary>
        public static void ClearCache()
        {
            // Indicates that all of the cache groups in the user's system should be enumerated
            const int CACHEGROUP_SEARCH_ALL = 0x0;
            // Indicates that all the cache entries that are associated with the cache group
            // should be deleted, unless the entry belongs to another cache group.
            const int CACHEGROUP_FLAG_FLUSHURL_ONDELETE = 0x2;
            // File not found.
            const int ERROR_FILE_NOT_FOUND = 0x2;
            // No more items have been found.
            const int ERROR_NO_MORE_ITEMS = 259;
            // Pointer to a GROUPID variable
            long groupId = 0;

            // Local variables
            int cacheEntryInfoBufferSizeInitial = 0;
            int cacheEntryInfoBufferSize = 0;
            IntPtr cacheEntryInfoBuffer = IntPtr.Zero;
            INTERNET_CACHE_ENTRY_INFOA internetCacheEntry;
            IntPtr enumHandle = IntPtr.Zero;
            bool returnValue = false;

            // Delete the groups first.
            // Groups may not always exist on the system.
            // For more information, visit the following Microsoft Web site:
            // http://msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp            
            // By default, a URL does not belong to any group. Therefore, that cache may become
            // empty even when the CacheGroup APIs are not used because the existing URL does not belong to any group.            
            enumHandle = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, ref groupId, IntPtr.Zero);
            // If there are no items in the Cache, you are finished.
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            // Loop through Cache Group, and then delete entries.
            while (true)
            {
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()) { break; }
                // Delete a particular Cache Group.
                returnValue = DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero);
                if (!returnValue && ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error())
                {
                    returnValue = FindNextUrlCacheGroup(enumHandle, ref groupId, IntPtr.Zero);
                }

                if (!returnValue && (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error() || ERROR_FILE_NOT_FOUND == Marshal.GetLastWin32Error()))
                    break;
            }

            // Start to delete URLs that do not belong to any group.
            enumHandle = FindFirstUrlCacheEntry(null, IntPtr.Zero, ref cacheEntryInfoBufferSizeInitial);
            if (enumHandle != IntPtr.Zero && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                return;

            cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
            cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);
            enumHandle = FindFirstUrlCacheEntry(null, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);

            while (true)
            {
                internetCacheEntry = (INTERNET_CACHE_ENTRY_INFOA)Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(INTERNET_CACHE_ENTRY_INFOA));
                if (ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error()) { break; }

                cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize;
                returnValue = DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName);
                if (!returnValue)
                {
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
                if (!returnValue && ERROR_NO_MORE_ITEMS == Marshal.GetLastWin32Error())
                {
                    break;
                }
                if (!returnValue && cacheEntryInfoBufferSizeInitial > cacheEntryInfoBufferSize)
            {
                    cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;
                    cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, (IntPtr)cacheEntryInfoBufferSize);
                    returnValue = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);
                }
            }
            Marshal.FreeHGlobal(cacheEntryInfoBuffer);
        }
        #endregion
    }
}

It is based heavily on the Microsoft KB article here:
http://support.microsoft.com/kb/326201

And to pre-empt the question – yes this is a huge pain in the neck, and no, there isn’t another way around it. Good luck!