运行多个任务并等待所有任务完成

Question

我需要运行多个任务来访问数据库并等待所有任务完成以获取结果并将其分配给我的视图模型，我尝试了很多示例但我从未得到结果，请帮助，这是我的代码

var model = new AggregationViewModel();
var loadDataTasks = new Task[]
{
    Task.Run(async () =>model.Alive =  await _repository.GetCountAsync<filter>(Predicate)),
    Task.Run(async () => model.Delay = await _repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused")))
};
try
{
    await Task.WhenAll(loadDataTasks);
    foreach (var item in loadDataTasks)
    {

    }
}
catch (Exception ex)
{
}

Answer 1

看看这个：

 var task1 = _repository.GetCountAsync<filter>(Predicate);
 var task2 = _repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused"));

 await Task.WhenAll(task1, task2); //wait both tasks to finish

 model.Alive = await task1;
 model.Delay = await task2;

PS：上面代码放置的函数，对于上面的场景需要异步。

Answer 2

试试这个代码：

var model = new AggregationViewModel();

//----------------------------------------
var tasks = new List<Task<int>>();
//Add CountA
tasks.Add(_repository.GetCountAsync<filter>(Predicate));
//Add CountB
tasks.Add(_repository.GetCountAsync<Flight>(predicate.And(x => x.Status == "refused")));

//----------------------------------------
// Create a task with "allTasks" name to wait to complete all tasks
Task allTasks = Task.WhenAll(tasks);
try {
    // Wait to compelete "allTask"
     allTasks.Wait();
}
catch(AggregateException) 
{}

//----------------------------------------
//Working on the results

if (allTasks.Status == TaskStatus.RanToCompletion) {
   model.CountA=allTasks.Result[0]
   model.CountB=allTasks.Result[1]
}
// Display information on faulted tasks.
else {
    foreach (var t in tasks) {
        Console.WriteLine("Task {0}: {1}", t.Id, t.Status);
     }
}