用URLDownloadToFile下载文件

'判断缓存是否存在
Private Declare Function GetUrlCacheEntryInfo Lib "wininet.dll" Alias "GetUrlCacheEntryInfoA" (ByVal sUrlName As String, lpCacheEntryInfo As Any, lpdwCacheEntryInfoBufferSize As Long) As Long
'删除缓存
Private Declare Function DeleteUrlCacheEntry Lib "wininet.dll" Alias "DeleteUrlCacheEntryA" (ByVal lpszUrlName As String) As Long
'上面二步后可以不从缓存下载数据，而是直接下载新的数据
Private Declare Function URLDownloadToFile Lib "urlmon" Alias "URLDownloadToFileA" (ByVal pCaller As Long, ByVal szURL As String, ByVal szFileName As String, ByVal dwReserved As Long, ByVal lpfnCB As Long) As Long

szUrl = "http://www.csdn.cn/test.txt";

DeleteUrlCacheEntry (szUrl); // 清理缓存
szFileName = "C:/dtapp.txt";

if (S_OK == URLDownloadToFile(NULL, szUrl, szFileName, NULL,NULL)) then
// 下载成功

else

// 下载失败
end if

清理和下载的路径要完全一样，才能直接下载新的数据！