多个任务的C＃异步问题

Question

I am trying to iterate over a list and trying to get data from async method. Following is the code :

var tasks = listOfStrings.Select(async currentString => {

       //creating an object RequestDataObj
        RequestDataObj request = new RequestDataObj();

       //filling RequestDataObj with some request data based on currentString

       //making async call and getting data in resultDataObj 
       var resultDataObj = await ApiCall.GetDataAsync(request, currentString);

       //saving resultDataObj + currentString to database synchronously
  });

await Task.WhenAll(tasks);
//doing some other operations here

Problem is that in database the value of currentString is always the last item of listOfStrings. Am I doing anything wrong? Please help.

Thanks

Answer 1

I believe you have a closure issue here. Try this instead:

var taskList = new List<Task>();
foreach (var myString in listOfStrings)
{
    // Avoid closure issue
    var temp = myString;
    taskList.Add(Task.Factory.StartNew(async object stringObject => {
        var currentString = stringObject as string;
        //creating an object RequestDataObj
        RequestDataObj request = new RequestDataObj();

        //filling RequestDataObj with some request data based on currentString

        //making async call and getting data in resultDataObj 
        var resultDataObj = await ApiCall.GetDataAsync(request, currentString);

        //saving resultDataObj + currentString to database synchronously
    }, temp));
}

await Task.WhenAll(taskList);
//doing some other operations here

There may be typos in the above; haven't tested it.