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Editorial Team
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Asked: 2026-05-16T11:42:22+00:00

I get the following exception when I open a file for unzipping it’s contents.

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I get the following exception when I open a file for unzipping it’s contents. It happens when I have the file selected in Windows Explorer, or mouse over it showing a tooltip.

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:

Is there a way just to wait until the file is no longer in use and then read it? Basically I just watch a folder for any new zip files, unzip the contents of the zip file, then delete it.

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;

Event handler:

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);
}
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1 Answer

  1. Editorial Team

    This is entirely normal when you use FileSystemWatcher. It is very likely that the file you get the notification for is in use by the process that created or modified the file. You will have to wait until the process stops using it. You of course cannot predict when that happens.

    A generic approach is to put the path to the file in a list that you periodically scan, triggered by a timer. Eventually you’ll get access to the file.

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