检查内部循环是否已创建 *txt 文件

Question

My code is searchcing inside a loop if a *txt file has been created. If file will not be created after x time then i will throw an exception. Here is my code:

 var AnswerFile = @"C:\myFile.txt";

 for (int i = 0; i <= 30; i++)
 {
     if (File.Exists(AnswerFile))
          break;
      await Task.Delay(100);
 }

 if (File.Exists(AnswerFile))
 {
 }
 else
 { 
 }

After the loop i check my file if has been created or not. Loop will expire in 3 seconds, 100ms * 30times. My code is working, i am just looking for the performance and quality of my code. Is there any better approach than mine? Example should i use FileInfo class instead this?

  var fi1 = new FileInfo(AnswerFile);
  if(fi1.Exists)
  {
  }

Or should i use filewatcher Class?

Answer 1

You should perhaps use a FileSystemWatcher for this and decouple the process of creating the file from the process of reacting to its presence. If the file must be generated in a certain time because it has some expiry time then you could make the expiry datetime part of the file name so that if it appears after that time you know it's expired. A note of caution with the FileSystemWatcher - it can sometimes miss something ( the fine manual says that events can be missed if large numbers are generated in a short time)

In the past I've used this for watching for files being uploaded via ftp. As soon as the notification of file created appears I put the file into a list and check it periodically to see if it is still growing - you can either look at the filesystem watcher lastwritetime event for this or directly check the size of the file now vs some time ago etc - in either approach it's probably easiest to use a dictionary to track the file and the previous size/most recent lastwritedate event. After a minute of no growth I consider the file uploaded completely and I process it. It might be wise for you to implement a similar delay if using a file system watcher and the files are arriving by some slow generating method

Answer 2

Why you don't retrieve a list of files name, then search in the list? You can use Directory.GetFiles to get the files list inside a directory then search in this list. This would be more fixable for you since you will create the list once, and reuse it across the application, instead of calling File.Exists for each file.

Example:

var path = @"C:\folder\"; // set the folder path, which contains all answers files

var ext = "*.txt"; // set the file extension. 
// GET filename list (bare name) and make them all lowercase.
var files = Directory.GetFiles(path, ext).Select(x=> x.Substring(path.Length, (x.Length - path.Length) - ext.Length + 1 ).Trim().ToLower()).ToList();


// Search for this filename 
var search = "myFile";

// Check 
if(files.Contains(search.ToLower()))
{
    Console.WriteLine($"File : {search} is already existed.");
}
else
{
    Console.WriteLine($"File : {search} is not found.");
}