Error Making Method Async

[Kevin Marois]

My app has a FileSystemWatcher. Once a file is dropped into the target folder it is then Ftp'd to the server. I'm trying to make it async but I'm getting errors. I want to make the method async so that multiple files can be uploaded without blocking.

class Program
{
private static string _address;
private static string _userName;
private static string _password;
static void Main(string[] args)
{
}
// A FileSystemWatcher passes the file name into this method
public static async void FileReceived(string fileName)
{
Task t = await Task.Run(() => FTPFile(fileName)); // <=== ERROR HERE
await t.ContinueWith((t1) =>
{
FileUploaded(t1.Result);
});
}
// FTP the file to the server
private static string FTPFile(string fileName)
{
string remoteFile = Path.GetFileName(fileName);
SFTP sftp = new SFTP(_address, _userName, _password);
sftp.UploadFileAsync(fileName, remoteFile);
return fileName;
}
private static async void FileUploaded(string fileName)
{
// Once here, the file has been transfered.
}
}

On the Task line I get the error:

Cannot implicitly convert type 'string' to 'System.Threading.Tasks.Task'

I'm not sure how to fix this. Can someone help? Thanks

If it's not broken, fix it until it is. Everything makes sense in someone's mind. Ya can't fix stupid.

[George Swan]

You should start the Task and then await it.

public static async void FileReceived(string fileName)
{
Task<string> t = Task.Run(() => FTPFile(fileName));
await t.ContinueWith((t1) =>
{
FileUploaded(t1.Result);
});
}

[Pete OHanlon]

Your FTPFile method returns a string. You're trying to put it in a Task of string.

This space for rent

[Richard Deeming]

You should avoid async void methods wherever possible: Avoid async void methods - You’ve Been Haacked[^] Async/Await - Best Practices in Asynchronous Programming[^] Also, sftp.UploadFileAsync implies that the method returns before the upload has completed. Does this method return a Task, or does it raise an UploadFileCompleted event? If it raises an event (EAP pattern), you can wrap that in a Task-returning method, and make your FTPFile method async as well. How to: Wrap EAP Patterns in a Task[^] Tasks and the Event-based Asynchronous Pattern | Parallel Programming with .NET[^]

public static class SFTPExtensions
{
public static Task UploadFileTaskAsync(this SFTP sftp, string fileName, string remoteFile)
{
var tcs = new TaskCompletionSource<bool>();

    UploadFileCompletedEventHandler handler = null;
    handler = (sender, args) =>
    {
        if (args.Cancelled)
        {
            tcs.TrySetCancelled();
        }
        else if (args.Error != null)
        {
            tcs.TrySetException(args.Error);
        }
        else
        {
            tcs.TrySetResult(true);
        }
        
        sftp.UploadFileCompleted -= handler;
    };
    
    sftp.UploadFileCompleted += handler;
    
    try
    {
        sftp.UploadFileAsync(fileName, remoteFile);
    }
    catch (Exception ex)
    {
        sftp.UploadFileCompleted -= handler;
        tcs.TrySetException(ex);
    }
    
    return tcs.Task;