HOW TO: Clear the Cache When Your Application Hosts a WebBrowser Control in Visual C# .NET (326201)


The information in this article applies to:

  • Microsoft Visual C# .NET (2002)
This article was previously published under Q326201
For a Microsoft Visual Basic .NET version of this article, see 311289.

This article refers to the following Microsoft .NET Framework Class Library namespace:
  • System.Runtime.InteropServices

IN THIS TASK

SUMMARY

This step-by-step article describes how to use WinInet application programming interface (API) functions to clear the cache directly.

You may have to clear the cache programmatically when your application hosts a WebBrowser control. However, this feature is not available through the interfaces of the WebBrowser control.

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WinInet Functions

To clear the cache directly, you can use the following WinInet functions:
  • Use the FindFirstURLCacheEntry function to find the first cache entry.
  • Use the FindNextUrlCacheEntry function to enumerate through the cache.
  • Use the DeleteUrlCacheEntry function to delete each entry.
The code sample in this article uses all of these functions.

NOTE: These functions are only available with Microsoft Internet Explorer 5. Therefore, you must include the appropriate checks (which the code sample in this article includes) to prevent errors.

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Steps to Clear the Cache in Visual C# .NET

To use the WinInet functions in Visual C# .NET to clear all of the files in the cache, follow these steps:
  1. Start Microsoft Visual Studio .NET.
  2. On the File menu, point to New, and then click Project.
  3. In the New Project dialog box, click Visual C# Projects under Project Types, and then click Console Application under Templates.
  4. Add the following code to the Class1.cs class:
    using System;
using System.Runtime.InteropServices;

// Visual C# version of Q326201
namespace Q326201CS
{
    // Class for deleting the cache.
    class DeleteCache
    {
        // For PInvoke: Contains information about an entry in the Internet cache
        [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 FILETIME LastModifiedTime;
            [FieldOffset(40)] public FILETIME ExpireTime;
            [FieldOffset(48)] public FILETIME LastAccessTime;
            [FieldOffset(56)] public 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);

        [STAThread]
        static void Main(string[] args)
        {
            // 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)
            {
                // 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));		

                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);		
        }
    }
}
  5. Compile and then run the project.
  6. To confirm that the temporary Internet files in your cache have been deleted, follow these steps in Microsoft Internet Explorer:
    1. On the Tools menu, click Internet Options.
    2. In the Temporary Internet files area on the General tab, click Settings.
    3. Click View Files. Notice that all of the files in the Internet Explorer cache have been deleted.
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REFERENCES

The code sample in this article uses the Interop namespace that is part of the Visual Studio .NET runtime. For more information, visit the following Microsoft Developer Network (MSDN) Web site:

Interoperating with Unmanaged Code
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconinteroperatingwithunmanagedcode.asp

For information about Microsoft .NET development, visit the following MSDN Web site:

.NET Development
http://msdn.microsoft.com/netframework/default.aspx

For more information about the syntax of the WinInet caching functions, visit the following MSDN Web site:

Caching
http://msdn.microsoft.com/library/?url=/workshop/networking/wininet/overview/cache.asp

For additional information%1, click the article number%2 below to view the article%2 in the Microsoft Knowledge Base:

262110 HOWTO: Clear Cache When Your Application Hosts a WebBrowser Control

For more information about developing Web-based solutions for Microsoft Internet Explorer, visit the following Microsoft Web sites:

http://msdn.microsoft.com/ie/

http://support.microsoft.com/iep

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Modification Type:MajorLast Reviewed:4/21/2006
Keywords:kbCaching kbCOMInterop kbhowto kbHOWTOmaster kbWebBrowser kbWinInet KB326201 kbAudDeveloper
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