判斷一個文件是否在IE的緩存中

　　當你建立一個聯到網上文件的快捷方式時，你可能需要知道它是否已經被訪問過，于是你就可以適當地改變鏈接的顏色等等。這則小技巧
就是告訴你如何判斷一個文件是否在Inte.net Explorer的緩存中，以滿足你的須要。
　　新建一個項目、添加一個模塊。將以下代碼寫到模塊里：

Private Const ERROR_INSUFFICIENT_BUFFER = 122
Private Const eeErrorBase = 26720

Private Type FILETIME
　 dwLowDateTime As Long
　 dwHighDateTime As Long
End Type

Private Type INTERNET_CACHE_ENTRY_INFO
　 dwStructSize As Long
　 lpszSourceUrlName As String
　 lpszLocalFileName As String
　 CacheEntryType As String
　 dwUseCount As Long
　 dwHitRate As Long
　 dwSizeLow As Long
　 dwSizeHigh As Long
　 LastModifiedTime As FILETIME
　 ExpireTIme As FILETIME
　 LastAccessTime As FILETIME
　 LastSyncTime As FILETIME
　 lpHeaderInfo As Long
　 dwHeaderInfoSize As Long
　 lpszFileExtension As String
　 dwReserved As Long
End Type

Private Declare Function GetUrlCacheEntryInfo Lib "wininet.dll" _
Alias "GetUrlCacheEntryInfoA" (ByVal sUrlName As String, _
　 lpCacheEntryInfo As Any, lpdwCacheEntryInfoBufferSize _
　 As Long) As Long

'用來報告API產生的錯誤：
Private Const FORMAT_MESSAGE_ALLOCATE_BUFFER = &H100
Private Const FORMAT_MESSAGE_ARGUMENT_ARRAY = &H2000
Private Const FORMAT_MESSAGE_FROM_HMODULE = &H800
Private Const FORMAT_MESSAGE_FROM_STRING = &H400
Private Const FORMAT_MESSAGE_FROM_SYSTEM = &H1000
Private Const FORMAT_MESSAGE_IGNORE_INSERTS = &H200
Private Const FORMAT_MESSAGE_MAX_WIDTH_MASK = &HFF
Private Declare Function FormatMessage Lib "kernel32" Alias _
　 "FormatMessageA" (ByVal dwFlags As Long, lpSource As Any, _
　 ByVal dwMessageId As Long, ByVal dwLanguageId As Long, _
　 ByVal lpBuffer As String, ByVal nSize As Long, Arguments _
　 As Long) As Long

Public Function WinAPIError(ByVal lLastDLLError As Long) As String
Dim sBuff As String
Dim lCount As Long

　 '返回與LastDLLError相關的出錯信息：
　 sBuff = String$(256, 0)
　 lCount = FormatMessage( _
　　　FORMAT_MESSAGE_FROM_SYSTEM Or FORMAT_MESSAGE_IGNORE_INSERTS, _
　　　0, lLastDLLError, 0&, sBuff, Len(sBuff), ByVal 0)
　 If lCount Then
　　　WinAPIError = Left$(sBuff, lCount)
　 End If

End Function

Public Function GetCacheEntryInfo(ByVal hWnd As Long, _
　 ByVal lpszUrl As String) As Boolean

Dim dwEntrySize As Long
Dim lpCacheEntry As INTERNET_CACHE_ENTRY_INFO
Dim dwTemp As Long
Dim lErr As Long

　 If (GetUrlCacheEntryInfo(lpszUrl, ByVal 0&, dwEntrySize)) = 0 Then
　　　lErr = Err.LastDllError
　　　If (lErr <> ERROR_INSUFFICIENT_BUFFER) Then
　　　　 '預料外的錯誤。須要顯示出錯原因：
　　　　 Err.Raise eeErrorBase + 1, _
　　　　　　App.EXEName & ".mCacheEntry", WinAPIError(lErr)

　　　　 GetCacheEntryInfo = False
　　　　 Exit Function
　　　Else
　　　　 '這是預料中的錯誤
　　　　 GetCacheEntryInfo = True
　　　End If
　 End If

End Function


在窗體上添加一個Command和一個Text。然后加入這些代碼：

Option Explicit

Private Sub Command1_Click()
On Error Goto ErrorHandler
　 '檢查Text中的URL地址是否出現在緩存中：
　 If (GetCacheEntryInfo(Me.hWnd, Text1.Text)) Then
　　　MsgBox "URL In Cache.", vbInformation
　 Else
　　　MsgBox "URL Not In Cache.", vbInformation
　 End If

Exit Sub

ErrorHandler:
　MsgBox "URL Not in Cache [" & Err.Description & "]",vbInformation

End Sub

　　運行，在Text中鍵入一個URL地址（比如，http://www.vbaccelerator.com/index.html）當你按下Command按鈕時，就會得到一則消息報告URL在不在緩存中。如果Windows給出了URL沒找到的原因，它將被顯示在隨后的的方括號內。