如何将所有等待 ViewModel 添加到 Task.WhenAll

Question

如何在 Task.WhenAll() 中添加这三个等待，但使用我的模型的 return 值，因为如果不在 WhenAll() 中添加它，我可以获得 return 我的模型。但是当在 Task.WhenAll() 中添加它时，我得到的只是一些 AsyncState、id 属性。

var _pending = await _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Pending);
var _cancel = await _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Cancel);
var _completed = await _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Completed);

List<Task> taskList = List<Task<StatusLookup>>();
taskList.Add(_lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Pending));
taskList.Add(_lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Cancel));
taskList.Add(_lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Completed));

var result = await Task.WhenAll(taskList);

谢谢

Answer 1

您在这里有一个答案：https://jeremylindsayni.wordpress.com/2019/03/11/using-async-await-and-task-whenall-to-improve-the-overall-speed-of-your-c-code/

为了用尽可能少的语言告诉它，您应该将任务（没有 await）分配给变量。然后用 WhenAll 等待他们，最后在 Result 属性.

中读取他们的结果

Answer 2

您可以在WhenAllreturns后阅读结果。您可以使用 await（在完成的任务上再次调用它不会执行任何操作）或从 Result.

中读取它

var pendingTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Pending);
var cancelTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Cancel);
var completedTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Completed);

await Task.WhenAll( new [] { pendingTask, cancelTask, completedTask } );

_pending = pendingTask.Result;
_cancel = cancelTask.Result;
_complete = completedTask.Result;

您甚至可以跳过 WhenAll。这会给你一个稍微不同的行为，但它可能同样有效：

var pendingTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Pending);
var cancelTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Cancel);
var completedTask = _lookupService.GetFirstOrDefaultAsync<StatusLookup>(x => x.Code == LookupConstants.Completed);

_pending = await pendingTask;
_cancel = await cancelTask;
_complete = await completedTask;