使用 File.OpenRead 打开文件时出现 System.IOException

Question

当我打开文件以解压缩其内容时，出现以下异常。当我在 Windows 资源管理器中选择文件或将鼠标悬停在显示工具提示的文件上时，就会发生这种情况。

System.IO.IOException was unhandled
  Message=The process cannot access the file 'D:\Documents\AutoUnZip\Zips\MVCContrib.Extras.release.zip' because it is being used by another process.
  Source=mscorlib
  StackTrace:
       at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
       at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
       at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
       at System.IO.File.OpenRead(String path)
       at AutoUnzip.SelectFolderForm.w_Changed(Object sender, FileSystemEventArgs e) in D:\Projects\WindowsForms\AutoUnzip\AutoUnzip\SelectFolderForm.cs:line 37
       at System.IO.FileSystemWatcher.OnCreated(FileSystemEventArgs e)
       at System.IO.FileSystemWatcher.NotifyFileSystemEventArgs(Int32 action, String name)
       at System.IO.FileSystemWatcher.CompletionStatusChanged(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* overlappedPointer)
       at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)
  InnerException: 

有没有办法等到文件不再使用时再读取它？基本上我只是查看文件夹中是否有新的 zip 文件，解压缩 zip 文件的内容，然后将其删除。

FileSystemWatcher watcher = new FileSystemWatcher("C:\\Path\\To\\Folder\\");
watcher.NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.FileName;
watcher.Filter = "*.zip";
watcher.Created += new FileSystemEventHandler(w_Changed);
// Begin watching.
watcher.EnableRaisingEvents = true;

事件处理程序：

void w_Changed(object sender, FileSystemEventArgs e)
{
    // IOException on following line
    using (ZipInputStream s = new ZipInputStream(File.OpenRead(e.FullPath)))
    {
        ...
    }
    // delete the zip file
    File.Delete(e.FullPath);
}

Answer 1

当您使用 FileSystemWatcher 时，这是完全正常的。您收到通知的文件很可能正在被创建或修改该文件的进程使用。您必须等到该进程停止使用它。你当然无法预测这种情况何时发生。

通用方法是将文件的路径放入由计时器触发的定期扫描的列表中。最终您将可以访问该文件。

Answer 2

有时，如果您只是复制错误抛出而不是使用 File.OpenRead 将其更改为：

void w_Changed(object sender, FileSystemEventArgs e) 
{ 
    // IOException on following line 
    using (ZipInputStream s = new ZipInputStream(new System.IO.FileStream(e.FullPath, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.ReadWrite))) 
    { 
        ... 
    } 
    // delete the zip file 
    File.Delete(e.FullPath); 
}