Question

使用Task的WhenAll（）或WaitAll（）方法时，有没有办法知道单个Task的状态。
当我为每个完成的任务使用await Task.WhenAll（tasks.ToArray（））时，我想知道任务已经完成。

Answer 1

有一种更好的方法可以做到这一点，但是这里有一个原始类，它接受一系列未启动的任务，并在每次执行某些任务时触发一个事件：

public class TaskBatchRunner
{
    private Task[] _tasks;

    public event EventHandler<Task> TaskCompleted;

    public TaskBatchRunner(Task[] tasks)
    {
        _tasks = tasks.Select(t =>
            new Task(() =>
            {
                t.ContinueWith(OnTaskCompleted);
                t.Start();
            })).ToArray();
    }

    public void Run()
    {
        foreach (var t in _tasks) t.Start();
        Task.WaitAll(_tasks);
    }

    private void OnTaskCompleted(Task completedTask)
    {
        TaskCompleted?.Invoke(this, completedTask);
    }
}

用法：

        var taskRunner = new TaskBatchRunner(tasks.ToArray());
        taskRunner.TaskCompleted += MyTaskCompleted;
        taskRunner.Run();
        ...

    private void MyTaskCompleted(object sender, Task e)
    {
        System.Diagnostics.Debug.WriteLine($"task {e.Id} completed!");
    }

Answer 2

要报告async或并发进程的进度，请使用IProgress<T>抽象。使用Progress<T> implmentation，您可以轻松捕获当前上下文，并在后台工作时在ui上下文中运行进度更新/完成表达式：

public class WorkItem {
    public async Task DoWork(IProgress<bool> completionNotification) {
        await Task.Delay(TimeSpan.FromSeconds(2));
        //Work Done
        completionNotification.Report(true);
    }

    //Get, Set, Fire Property change etc
    public bool Completed {
        get; set;
    }
}

public class ViewModel {
    public async void ButtonClickHandler(object sender, EventArgs e) {
        var workitemTasks = WorkItems.Select(workItem =>
            workItem.DoWork(new Progress<bool>(done => workItem.Completed = done)))
            .ToList();
        await Task.WhenAll(workitemTasks);
    }

    //Get, Set, Fire Property change etc
    public IEnumerable<WorkItem> WorkItems {
        get; set;
    }
}

<强> More Info

<强> Reporting Progress From Async Tasks @StephenCleary

报告任务进度

2 个答案: