Internet技巧两则

　　一、判断某一个连接是否保存在Cache中

　　在使用Microsoft IE在网上冲浪时，IE会把你浏览过的网页保存在Cache中以便你可以脱机浏览。
　　下面这个程序可以判断一个URL是否在浏览器的Cache中。
　　首先建立一个新的VB工程文件，在Form1中加入一个CommandButton控件和一个TextBox控件，然后
　　在Form1的代码窗口中加入以下代码：

Option Explicit

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

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

´获取错误消息
　　 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
　　 ´URL没有在Cache中
　　 Err.Raise eeErrorBase + 1, App.EXEName & ".mCacheEntry", WinAPIError(lErr)
　　 GetCacheEntryInfo = False
　　 Exit Function
　　 Else
　　 ´URL保存在Cache中
　　 GetCacheEntryInfo = True
　　 End If
　　 End If
　　 End Function

Private Sub Command1_Click()
　　 On Error GoTo ErrorHandler
　　 If (GetCacheEntryInfo(Me.hWnd, Text1.Text)) Then
　　 MsgBox "URL 保存在Cache中.", vbInformation
　　 Else
　　 MsgBox "URL 没有保存在Cache中.", vbInformation
　　 End If

Exit Sub

ErrorHandler:
　　 MsgBox "URL 没有保存在Cache中 [" & Err.Description & "]", vbInformation
　　 End Sub
　　

Private Sub Form_Load()
　　 Form1.CurrentX = 150: Form1.CurrentY = 60
　　 Form1.Print "在Text1中输入URL，按Command1检测"
　　 Text1.Text = ""
　　 Command1.Default = True
　　 End Sub

　　运行程序，在TextBox中输入URL地址（例如http://member.netease.com/~blackcat），然后点击Command1按钮，如果URL在Cache中，程序会弹出消息框显示URL 保存在Cache中。