如何在没有基于任务的代理的情况下处理Windows Phone 8中的服务引用

Question

With so much emphasis on Task-Based asynchronous development, I was surprised to see that Service References in Windows Phone 8 do not support task-based implementations. Instead they use a "XYZCompleted" event-based asynchronous approach.

As a result, code like this is necessary: http://codepaste.net/fqyt47

public async Task<IEnumerable<MyService.Character>> GetCharactersAsync()
{
    var _Task = new TaskCompletionSource<IEnumerable<MyService.Character>>();
    var _Client = new MyService.ServiceClient();
    _Client.GetCharactersCompleted += (s, e) =>
    {
        var _Characters = e.Result as IEnumerable<MyService.Character>;
        if (e.Error != null && !_Task.TrySetException(e.Error))
            System.Diagnostics.Debugger.Break();
        else if (e.Cancelled && !_Task.TrySetCanceled())
            System.Diagnostics.Debugger.Break();
        else if (!_Task.TrySetResult(_Characters))
            System.Diagnostics.Debugger.Break();
    };
    _Client.GetCharactersAsync();

    return await _Task.Task;
}

However, this feels wrong . Is there a better, more elegant approach?

Answer 1

I'm surprised Windows Phone 8 doesn't have Task -based reference creation.

That said, TaskCompletionSource is the standard way of interoperating with various asynchronous patterns (including EAP) .

Usually it's done with extension methods which are consumable by await but which are not async themselves:

public Task<IEnumerable<MyService.Character>> GetCharactersTaskAsync(this ServiceClient client)
{
  var tcs = new TaskCompletionSource<IEnumerable<MyService.Character>>();
  client.GetCharactersCompleted += (s, e) =>
  {
    if (e.Error != null) tcs.SetException(e.Error);
    else if (e.Cancelled) tcs.SetCanceled();
    else tcs.SetResult(e.Result);
  };
  client.GetCharactersAsync();
  return tcs.Task;
}