wp8的工作queue列？ [英] Task queue for wp8?

问题描述

在wp8中将复杂任务排队的正确方法是什么？

What is a correct way to queue complex tasks in wp8?

任务包括以下内容：

1. 通过更新模型变量显示 ProgressIndicator


2. 获取数据或将数据存储到wcf服务中（ UploadStringAsync ）


3. 使用 UploadStringCompleted 的结果更新潜在的数据绑定模型。


4. 通过更新模型变量来隐藏 ProgressIndicator

1. Showing a ProgressIndicator through updating a model variable
2. Fetching or storing data to a wcf service (UploadStringAsync)
3. Updating potentially data bound model with the result from UploadStringCompleted.
4. Hiding the ProgressIndicator through updating a model variable

当前，我正在与拥有命令对象队列的类一起工作，运行一个线程，该线程在添加项（如果尚未运行）时启动。

Currently I've been working with a class owning a queue of command objects, running a single thread that is started when an item is added if it's not already running.

但是我在等待代码停止运行的任务或子任务时遇到问题。

I have however problems with waiting for tasks or subtasks where the code stops running.

以前我使用过async await，但是在行为上有几层变得越来越不可预测。

Previously I've used async await, but a few levels down the behaviour was becoming more and more unpredictable.

我想要的是主线程能够创建和排队命令对象。
命令对象应该一次运行一个，而不要先启动一个新对象，直到前一个完全完成。
如果需要，命令对象应该能够使用调度程序访问主线程。

What I want is the main thread being able to create and queue command objects. The command objects should run one at a time, not starting a new one until the previous one is completely finished. The command objects should be able to use the dispatcher to access the main thread if neccesary.

推荐答案

如果使用 async / await ，不需要其他线程（因为您没有CPU绑定处理）。

If you use async/await, there's no need for another thread (since you have no CPU-bound processing).

在您的情况下，听起来您只需要一个异步委托队列。异步委托的自然类型是 Func< Task> （无返回值）或 Func< Task< T>> （带有返回值）。不幸的是，这个小技巧目前还不为人所知。

In your case, it sounds like you just need a queue of asynchronous delegates. The natural type of an asynchronous delegate is Func<Task> (without a return value) or Func<Task<T>> (with a return value). This little tip is unfortunately not well-known at this point.

因此，声明一个异步委托队列：

So, declare a queue of asynchronous delegates:

private readonly Queue<Func<Task>> queue = new Queue<Func<Task>>();

然后，您可以拥有一个仅（异步）处理队列的顶级任务：

Then you can have a single "top-level" task that just (asynchronously) processes the queue:

private Task queueProcessor;

queueProcessor 可以为 null 每当没有其他项目时。每当它不是 null 时，它将代表此方法：

The queueProcessor can be null whenever there's no more items. Whenever it's not null, it'll represent this method:

private async Task ProcessQueue()
{
  try
  {
    while (queue.Count != 0)
    {
      Func<Task> command = queue.Dequeue();
      try
      {
        await command();
      }
      catch (Exception ex)
      {
        // Exceptions from your queued tasks will end up here.
        throw;
      }
    }
  }
  finally
  {
    queueProcessor = null;
  }
}

您的入队方法将如下所示：

private void Enqueue(Func<Task> command)
{
  queue.Enqueue(command);
  if (queueProcessor == null)
    queueProcessor = ProcessQueue();
}

现在，我有这样的异常处理设置：任何排队的命令引发异常将导致队列处理器停止处理（具有相同的异常）。这可能不是您应用程序的最佳行为。

Right now, I have the exception handling set up like this: any queued command that throws an exception will cause the queue processor to stop processing (with the same exception). This may not be the best behavior for your application.

您可以这样使用它（当然可以使用lambda或实际方法）：

You can use it like this (with either a lambda or an actual method, of course):

Enqueue(async () =>
{
  ShowProgressIndicator = true;
  ModelData = await myProxy.DownloadStringTaskAsync();
  ShowProgressIndicator = false;
});

请注意使用 DownloadStringTaskAsync 。如果您为您的EAP成员编写TAP包装器，则您的 async 代码将看起来更自然（即更简单）。

Note the use of DownloadStringTaskAsync. If you write TAP wrappers for your EAP members, your async code will be more "natural-looking" (i.e., simpler).

这太复杂了，我想建议将其放在单独的类中，但您首先要决定如何处理（和显示）错误。

This is sufficiently complex that I'd recommend putting it into a separate class, but you'd want to decide how to handle (and surface) errors first.

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