Microsoft KB Archive/326201

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

Article ID: 326201

Article Last Modified on 11/22/2007

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APPLIES TO


 * Microsoft Visual C# .NET 2002 Standard Edition

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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
 * WinInet Functions
 * Steps to Clear the Cache in Visual C# .NET

REFERENCES



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:  Start Microsoft Visual Studio .NET. On the File menu, point to New, and then click Project. In the New Project dialog box, click Visual C# Projects under Project Types, and then click Console Application under Templates.  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(@&quot;wininet&quot;,           SetLastError=true,            CharSet=CharSet.Auto,            EntryPoint=&quot;FindFirstUrlCacheGroup&quot;,            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(@&quot;wininet&quot;,           SetLastError=true,            CharSet=CharSet.Auto,            EntryPoint=&quot;FindNextUrlCacheGroup&quot;,            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(@&quot;wininet&quot;,            SetLastError=true,             CharSet=CharSet.Auto,             EntryPoint=&quot;DeleteUrlCacheGroup&quot;,             CallingConvention=CallingConvention.StdCall)] public static extern bool DeleteUrlCacheGroup(           long GroupId,            int dwFlags,            IntPtr lpReserved);

// For PInvoke: Begins the enumeration of the Internet cache [DllImport(@&quot;wininet&quot;,           SetLastError=true,            CharSet=CharSet.Auto,            EntryPoint=&quot;FindFirstUrlCacheEntryA&quot;,            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(@&quot;wininet&quot;,           SetLastError=true,            CharSet=CharSet.Auto,            EntryPoint=&quot;FindNextUrlCacheEntryA&quot;,            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(@&quot;wininet&quot;,           SetLastError=true,            CharSet=CharSet.Auto,            EntryPoint=&quot;DeleteUrlCacheEntryA&quot;,            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); }   } }                     Compile and then run the project. To confirm that the temporary Internet files in your cache have been deleted, follow these steps in Microsoft Internet Explorer:  On the Tools menu, click Internet Options.</li> In the Temporary Internet files area on the General tab, click Settings.</li> Click View Files. Notice that all of the files in the Internet Explorer cache have been deleted.</li></ol> </li></ol>

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