如何清除高速缓存时应用程序主机 web 浏览器控件

微凉

当您的应用程序承载 web 浏览器控件时，可能需要以编程方式清除缓存。此功能不能通过 web 浏览器控件的接口。本文介绍了如何使用 WinInet API 函数直接清除缓存。
使用 WinInet API FindFirstURLCacheEntry 查找第一个缓存项，并使用 FindNextUrlCacheEntry 枚举通过缓存。若要删除的每个条目使用 DeleteUrlCacheEntry。

请注意在下面的示例中使用 FindFirstUrlCacheGroup、 FindNextUrlCacheGroup 和 DeleteUrlCacheGroup。因此若要防止出现错误需要正确的检查，如图所示，这些 API 函数仅有成为可用的 Internet Explorer 5。

以下步骤显示如何在 Visual Basic 中使用 WinInet API，以清除高速缓存中的所有文件。

• 创建一个新的 Visual Basic 标准 EXE 项目。
• 创建在 form1 下的一个命令按钮。
• 将以下代码粘贴到 form1 的模块中：
  

Option Explicit

Private Declare Function FindFirstUrlCacheGroup Lib "wininet.dll" ( _
    ByVal dwFlags As Long, _
    ByVal dwFilter As Long, _
    ByRef lpSearchCondition As Long, _
    ByVal dwSearchCondition As Long, _
    ByRef lpGroupId As Date, _
    ByRef lpReserved As Long) As Long

Private Declare Function FindNextUrlCacheGroup Lib "wininet.dll" ( _
    ByVal hFind As Long, _
    ByRef lpGroupId As Date, _
    ByRef lpReserved As Long) As Long
   
Private Declare Function DeleteUrlCacheGroup Lib "wininet.dll" ( _
    ByVal sGroupID As Date, _
    ByVal dwFlags As Long, _
    ByRef lpReserved As Long) As Long
   
Private Declare Function FindFirstUrlCacheEntry Lib "wininet.dll" Alias "FindFirstUrlCacheEntryA" ( _
    ByVal lpszUrlSearchPattern As String, _
    ByRef lpFirstCacheEntryInfo As INTERNET_CACHE_ENTRY_INFO, _
    ByRef lpdwFirstCacheEntryInfoBufferSize As Long) As Long
   
Private Type INTERNET_CACHE_ENTRY_INFO
    dwStructSize As Long
    szRestOfData(1024) As Long
End Type

Private Declare Function DeleteUrlCacheEntry Lib "wininet.dll" Alias "DeleteUrlCacheEntryA" ( _
    ByVal lpszUrlName As Long) As Long

Private Declare Function FindNextUrlCacheEntry Lib "wininet.dll" Alias "FindNextUrlCacheEntryA" ( _
    ByVal hEnumHandle As Long, _
    ByRef lpNextCacheEntryInfo As INTERNET_CACHE_ENTRY_INFO, _
    ByRef lpdwNextCacheEntryInfoBufferSize As Long) As Long

Private Const CACHGROUP_SEARCH_ALL = &H0
Private Const ERROR_NO_MORE_FILES = 18
Private Const ERROR_NO_MORE_ITEMS = 259
Private Const CACHEGROUP_FLAG_FLUSHURL_ONDELETE = &H2
Private Const BUFFERSIZE = 2048

Private Sub Command1_Click()
    Dim sGroupID As Date
    Dim hGroup As Long
    Dim hFile As Long
    Dim sEntryInfo As INTERNET_CACHE_ENTRY_INFO
    Dim iSize As Long
        
    On Error Resume Next
   
    ' Delete the groups
    hGroup = FindFirstUrlCacheGroup(0, 0, 0, 0, sGroupID, 0)
   
    ' To avoid error using it with IE4 as FindFirstUrlCacheGroup is not implemented
    If Err.Number <> 453 Then
        If (hGroup = 0) And (Err.LastDllError <> 2) Then
            MsgBox "An error occurred enumerating the cache groups" & Err.LastDllError
            Exit Sub
        End If
    Else
        Err.Clear
    End If
   
    If (hGroup <> 0) Then
        'we succeeded in finding the first cache group.. enumerate and
        'delete
        Do
            If (0 = DeleteUrlCacheGroup(sGroupID, CACHEGROUP_FLAG_FLUSHURL_ONDELETE, 0)) Then
               
               ' To avoid error using it with IE4 as FindFirstUrlCacheGroup is not implemented
               If Err.Number <> 453 Then
                 MsgBox "Error deleting cache group " & Err.LastDllError
                 Exit Sub
               Else
                  Err.Clear
               End If
            End If
            iSize = BUFFERSIZE
            If (0 = FindNextUrlCacheGroup(hGroup, sGroupID, iSize)) And (Err.LastDllError <> 2) Then
                MsgBox "Error finding next url cache group! - " & Err.LastDllError
            End If
        Loop Until Err.LastDllError = 2
    End If
  
  ' Delete the files
    sEntryInfo.dwStructSize = 80
    iSize = BUFFERSIZE
    hFile = FindFirstUrlCacheEntry(0, sEntryInfo, iSize)
    If (hFile = 0) Then
        If (Err.LastDllError = ERROR_NO_MORE_ITEMS) Then
            GoTo done
        End If
        MsgBox "ERROR: FindFirstUrlCacheEntry - " & Err.LastDllError
        Exit Sub
    End If
    Do
        If (0 = DeleteUrlCacheEntry(sEntryInfo.szRestOfData(0))) _
            And (Err.LastDllError <> 2) Then
            Err.Clear
        End If
        iSize = BUFFERSIZE
        If (0 = FindNextUrlCacheEntry(hFile, sEntryInfo, iSize)) And (Err.LastDllError <> ERROR_NO_MORE_ITEMS) Then
            MsgBox "Error:  Unable to find the next cache entry - " & Err.LastDllError
            Exit Sub
        End If
    Loop Until Err.LastDllError = ERROR_NO_MORE_ITEMS
done:
    MsgBox "cache cleared"
    Command1.Enabled = True
End Sub

4.运行您的项目，然后单击 Command1。在您的计算机中高速缓存将被清除。

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