c# - The 'await' operator can only be used with an async lambda expression -

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• the 'await' operator can used within async lambda expression 1 answer

i'm trying copy list of files directory. i'm using async / await. i've been getting compilation error

the 'await' operator can used within async lambda expression. consider marking lambda expression 'async' modifier.

this code looks like

async task<int> copyfilestofolder(list<string> filelist,              iprogress<int> progress, cancellationtoken ct) {     int totalcount = filelist.count;     int processcount = await task.run<int>(() =>     {         int tempcount = 0;         foreach (var file in filelist)         {             string outputfile = path.combine(outputpath, file);              await copyfileasync(file, outputfile); //<-- error: compilation error               ct.throwifcancellationrequested();             tempcount++;             if (progress != null)             {                 progress.report((tempcount * 100 / totalcount)));             }          }          return tempcount;     });     return processcount; }   private async task copyfileasync(string sourcepath, string destinationpath) {     using (stream source = file.open(sourcepath, filemode.open))     {         using (stream destination = file.create(destinationpath))         {             await source.copytoasync(destination);         }     }  } 

pls can point out missing here ?

int processcount = await task.run<int>(() => 

should be

int processcount = await task.run<int>(async () => 

remember lambda shorthand defining method. so, outer method async, in case you're trying use await within lambda (which different method outer method). lambda must marked async well.