How to force FileSystemWatcher to wait till the fi

问题:

I am downloading a file and want to execute the install only after the download is complete. How do I accomplish this? Seems like FileSystemWatcher onCreate event would do this but this happens in a different thread, is there a simple way to force the waiting part to happen in the same thread.

Code I have so far

 FileSystemWatcher w = new FileSystemWatcher(@"C:/downloads");
 w.EnableRaisingEvents = true;
 w.Created += new FileSystemEventHandler(FileDownloaded);

 static void FileDownloaded(object source, FileSystemEventArgs e)
 {
    InstallMSI(e.FullPath);
 }

I looked at SynchronizingObject and WaitForChangedResult but didn't get a solid working sample.

回答1:

Try:

FileInfo fInfo = new FileInfo(e.FullPath); 
while(IsFileLocked(fInfo)){
     Thread.Sleep(500);     
}
InstallMSI(e.FullPath);


static bool IsFileLocked(FileInfo file)
{
    FileStream stream = null;
    try {
        stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
    }
    catch (IOException) {
        return true;
    }
    finally {
        if (stream != null)
            stream.Close();
    }   
    return false;
}

回答2:

If you insist on using FileSystemWatcher you would probably have to account for the fact that a file of some size isn't created (uploaded) in one single operation. The filesystem is likely to produce 1 created and x changed events before the file is ready for use.

You could catch the created events and create new (dedicated) threads (unless you already have an ongoing thread for that file) in which you loop and periodically try to open the file exclusively. If you succeed, the file is ready.

回答3:

One technique would be to download to the temporary directory, and then move it into C:/downloads once it was complete.

回答4:

If you are using WebClient to download, you can use set the client's DownloadFileCompleted eventhandler.
If you do it this way you can also use client.DownloadFileAsync() to make it download asynchronously.