WebBrowser control caching issue

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

Further to Serj Sagan, here is the code with bizarre error handling simplified, the infinite loop removed, and 32/64-bit capable.

/** * Modified from code originally found here: http://support.microsoft.com/kb/326201 **/ public class WebBrowserHelper {     #region Definitions/DLL Imports     /// <summary>     /// For PInvoke: Contains information about an entry in the Internet cache     /// </summary>     [StructLayout(LayoutKind.Explicit)]     public struct ExemptDeltaOrReserverd     {         [FieldOffset(0)]         public UInt32 dwReserved;         [FieldOffset(0)]         public UInt32 dwExemptDelta;     }      [StructLayout(LayoutKind.Sequential)]     public struct INTERNET_CACHE_ENTRY_INFOA     {         public UInt32 dwStructSize;         public IntPtr lpszSourceUrlName;         public IntPtr lpszLocalFileName;         public UInt32 CacheEntryType;         public UInt32 dwUseCount;         public UInt32 dwHitRate;         public UInt32 dwSizeLow;         public UInt32 dwSizeHigh;         public FILETIME LastModifiedTime;         public FILETIME ExpireTime;         public FILETIME LastAccessTime;         public FILETIME LastSyncTime;         public IntPtr lpHeaderInfo;         public UInt32 dwHeaderInfoSize;         public IntPtr lpszFileExtension;         public ExemptDeltaOrReserverd dwExemptDeltaOrReserved;     }      // 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      /// <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;         const int ERROR_INSUFFICIENT_BUFFER = 0x7A;          // 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.                     long groupId = 0;         IntPtr enumHandle = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL, IntPtr.Zero, 0, ref groupId, IntPtr.Zero);         if (enumHandle != IntPtr.Zero) {             bool more;             do {                 // Delete a particular Cache Group.                 DeleteUrlCacheGroup(groupId, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, IntPtr.Zero);                 more = FindNextUrlCacheGroup(enumHandle, ref groupId, IntPtr.Zero);             } while (more);         }          // Start to delete URLs that do not belong to any group.         int cacheEntryInfoBufferSizeInitial = 0;         FindFirstUrlCacheEntry(null, IntPtr.Zero, ref cacheEntryInfoBufferSizeInitial);  // should always fail because buffer is too small         if (Marshal.GetLastWin32Error() == ERROR_INSUFFICIENT_BUFFER) {             int cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;             IntPtr cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);             enumHandle = FindFirstUrlCacheEntry(null, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);             if (enumHandle != IntPtr.Zero) {                 bool more;                 do {                     INTERNET_CACHE_ENTRY_INFOA internetCacheEntry = (INTERNET_CACHE_ENTRY_INFOA)Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(INTERNET_CACHE_ENTRY_INFOA));                     cacheEntryInfoBufferSizeInitial = cacheEntryInfoBufferSize;                     DeleteUrlCacheEntry(internetCacheEntry.lpszSourceUrlName);                     more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);                     if (!more && Marshal.GetLastWin32Error() == ERROR_INSUFFICIENT_BUFFER) {                         cacheEntryInfoBufferSize = cacheEntryInfoBufferSizeInitial;                         cacheEntryInfoBuffer = Marshal.ReAllocHGlobal(cacheEntryInfoBuffer, (IntPtr)cacheEntryInfoBufferSize);                         more = FindNextUrlCacheEntry(enumHandle, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSizeInitial);                     }                 } while (more);             }             Marshal.FreeHGlobal(cacheEntryInfoBuffer);         }     } } 

Answer 2

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!