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I am trying to upload files to Azure Blob Storage and after successful upload adding the filename to a list for my further operation. When i am doing synchronous it works fine but when i am doing async the error occured.
Error : Collection was modified; enumeration operation may not execute.
foreach(var file in files)
   // .....
   await blockBlob.UploadFromStreamAsync(fs);

if (listOfMovedLabelFiles.Count > 0) // error point
    // my code for further operation

Is there any way to wait till all the async operations get completed.
Updated 5-Jun-14 5:52am
Sampath Lokuge 5-Jun-14 7:03am    
Is this forms or MVC ?
Vi(ky 5-Jun-14 7:04am    
It is console application.
Herman<T>.Instance 5-Jun-14 8:06am    
because of asynchronity your lists expands in the background. Better do the job in the background and raise an event when a filename must be added to the list
Rahul Kumar 5-Jun-14 10:28am    
and how to implement it, any sample or link.
Herman<T>.Instance 5-Jun-14 18:15pm    
what is the problem for you, the async or the event?

1 solution

If it's a console app then you have to use Async is as below.

Note: This is just a sample.Adjust it according to your app.

class Program
  static int Main(string[] args)
      return AsyncContext.Run(() => MainAsync(args));
    catch (Exception ex)
      return -1;

  static async Task<int> MainAsync(string[] args)

Read for more info : Async Console Programs
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