xamarin UIButton事件异步问题 - waitingforactivation

Question

我正在使用xamarin处理有关iphone应用程序开发的一些视频教程，我似乎遇到了异步问题。

我有一个按钮，当点击时会运行一个生成http请求的异步方法。但是，当单击时，异步方法永远不会运行，当我检查状态时它会显示“waitingforactivation”

public class RootViewModel : UIViewController
{
    private UIButton _button;
    private string response;

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        Title = "Load Async";
        View.BackgroundColor = UIColor.DarkGray;

        _button = new UIButton(UIButtonType.RoundedRect);
        _button.Frame = new RectangleF(0, View.Bounds.Height - 60, View.Bounds.Width, 60);
        _button.BackgroundColor = UIColor.FromRGB(0, 0, 0);
        _button.SetTitle("Get Async", UIControlState.Normal);
        _button.SetTitleColor(UIColor.FromRGB(255, 255, 255), UIControlState.Normal);

        response = string.Empty;

        _button.TouchUpInside += async (sender, args) =>
        {
            response = await DoStuffAsync();
            Title = response;
        };

        View.AddSubview(_button);
    }

    private async Task<string> DoStuffAsync()
    {
        var url = @"http://www.google.co.uk";

        using (var client = new HttpClient())
        {
            var response = await client.GetStringAsync(url);
            return response.Substring(0, 10);
        }
    }
}

非常感谢任何有关失败原因的帮助。