Question

我必须检查一组文件路径是否代表现有文件。

除非路径包含不在当前网络上的计算机上的网络共享，否则它可以正常工作。在这种情况下，超时需要很长时间（30或60秒）。

问题

有没有办法缩短非现有网络共享的超时时间？（我确信当他们存在时他们会很快回答，所以超时1秒就可以了）
在没有开始缓存并使算法更复杂的情况下，还有其他方法可以解决此问题吗？（即，我已经知道这些X网络共享不存在，跳过其余的匹配路径）

更新：使用线程工作，虽然不是特别优雅，但

public bool pathExists(string path) 
{
    bool exists = true;
    Thread t = new Thread
    (
        new ThreadStart(delegate () 
        {
            exists = System.IO.File.Exists(path); 
        })
    );
    t.Start();
    bool completed = t.Join(500); //half a sec of timeout
    if (!completed) { exists = false; t.Abort(); }
    return exists;
}

此解决方案避免了每次尝试需要一个线程，首先检查哪些驱动器可以访问并将其存储在某处。

Experts exchange solution

首先，您可以在IsDriveReady函数中设置“超时”值。我把它设置为5秒，但设置它适合任何适合你的。

下面使用了3种方法：

第一个是获取的WNetGetConnection API函数驱动器的UNC（\ servername \ share）
第二个是我们的主要方法：Button1_Click事件
第三个是ping服务器的IsDriveReady功能。

这对我很有用！你走了：

'This API Function will be used to get the UNC of the drive
Private Declare Function WNetGetConnection Lib "mpr.dll" Alias _
"WNetGetConnectionA" _
(ByVal lpszLocalName As String, _
ByVal lpszRemoteName As String, _
ByRef cbRemoteName As Int32) As Int32


'This is just a button click event - add code to your appropriate event
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

    Dim bIsReady As Boolean = False

    For Each dri As IO.DriveInfo In IO.DriveInfo.GetDrives()

        'If the drive is a Network drive only, then ping it to see if it's ready.
        If dri.DriveType = IO.DriveType.Network Then

            'Get the UNC (\\servername\share) for the 
            '    drive letter returned by dri.Name
            Dim UNC As String = Space(100)
            WNetGetConnection(dri.Name.Substring(0, 2), UNC, 100)

            'Presuming the drive is mapped \\servername\share
            '    Parse the servername out of the UNC
            Dim server As String = _
                 UNC.Trim().Substring(2, UNC.Trim().IndexOf("\", 2) - 2)

            'Ping the server to see if it is available
            bIsReady = IsDriveReady(server)

        Else
            bIsReady = dri.IsReady

        End If

        'Only process drives that are ready
        If bIsReady = True Then
            'Process your drive...
            MsgBox(dri.Name & " is ready:  " & bIsReady)

        End If

    Next

    MsgBox("All drives processed")

End Sub

Private Function IsDriveReady(ByVal serverName As String) As Boolean
    Dim bReturnStatus As Boolean = False

    '***  SET YOUR TIMEOUT HERE  ***
    Dim timeout As Integer = 5    '5 seconds

    Dim pingSender As New System.Net.NetworkInformation.Ping()
    Dim options As New System.Net.NetworkInformation.PingOptions()

    options.DontFragment = True

    'Enter a valid ip address
    Dim ipAddressOrHostName As String = serverName
    Dim data As String = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
    Dim buffer As Byte() = System.Text.Encoding.ASCII.GetBytes(data)
    Dim reply As System.Net.NetworkInformation.PingReply = _
                pingSender.Send(ipAddressOrHostName, timeout, buffer, options)

    If reply.Status = Net.NetworkInformation.IPStatus.Success Then
        bReturnStatus = True

    End If

    Return bReturnStatus
End Function

Answer 1

简而言之

构建可用驱动器列表。
尝试将此驱动器号解析为UNC名称。
尝试ping驱动器。

关于比尔评论的编辑

如果Google不是引用者，则EE不会免费显示答案。 EE的链接没有帮助。

the source code for the solution

Answer 2

使用线程进行检查。我认为线程可以超时。

Answer 3

这对我来说很有用！这是C＃中的IsDriveReady（）：

using System.Net;
private bool IsDriveReady(string serverName)
{
   // ***  SET YOUR TIMEOUT HERE  ***     
   int timeout = 5;    // 5 seconds 
   System.Net.NetworkInformation.Ping pingSender = new System.Net.NetworkInformation.Ping();
   System.Net.NetworkInformation.PingOptions options = new System.Net.NetworkInformation.PingOptions();
   options.DontFragment = true;      
   // Enter a valid ip address     
   string ipAddressOrHostName = serverName;
   string data = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
   byte[] buffer = System.Text.Encoding.ASCII.GetBytes(data);
   System.Net.NetworkInformation.PingReply reply = pingSender.Send(ipAddressOrHostName, timeout, buffer, options);
   return (reply.Status == System.Net.NetworkInformation.IPStatus.Success);
}

Answer 4

我发现带有线程超时功能的pathExists非常有用但终于意识到它需要从File.Exists更改为Directory.Exists才能正常工作。

Answer 5

另一个“线程解决方案”：

Sub test()
With Sheets("Feuil1")
    .Range("B1").Value = WorksheetFunction.VLookup(.Range("A1").Value, Sheets("Feuil2").Range("A1:B100"), 2, False)
End With
End Sub

来源：http://www.jonathanantoine.com/2011/08/18/faster-file-exists/

对于“驱动器响应速度不够快”存在一些担忧，因此这是速度与“真相”之间的折衷。如果您想确定100％，请不要使用它。

Answer 6

难道你不能只使用FileMonitor控件，以便在删除事件时触发事件吗？然后你可以将bool设置为false;

为非现有网络共享加速File.Exists

Experts exchange solution

6 个答案:

简而言之

关于比尔评论的编辑