如何在 silverlight 中同步 WebService 操作？

Question

我现在正在进行一个关于使用 Silverlight 和 Web 服务（asmx 页面）控制设备的项目。项目流程如下：

按下silverlight UI上的按钮，它会通过socket发送一个包到中间线。然后 middlewire 将接受包并解构它并将另一个包返回给 silverlight UI。我正在使用下面的代码来加载按钮状态，这将触发数据库查询：

 private ButtonStateModel _buttonStateModel = new ButtonStateModel() { BtnOneImage = "Skins/images/flag/QU.png", BtnOneVisible = Visibility.Visible, BtnTwoVisible = Visibility.Collapsed };
    public ButtonStateModel ButtonStateModel
    {
        get
        {
                    ButtonStateModel btnState = null;
                    dataService.GetPR(BusEquipmentPermission.Control.RtuID, BusEquipmentPermission.Control.DevID, (result) =>
                    {
                        if (result != null && result.Count > 0)
                        {
                            var flag = result[0].PRFlag;
                            if (flag == 1)
                            {
                                btnState = new ButtonStateModel()
                                {
                                    BtnOneImage = "Skins/images/flag/OP.png",
                                    BtnOneVisible = Visibility.Visible,
                                    BtnTwoImage = "Skins/images/flag/OFF.png",
                                    BtnTwoVisible = Visibility.Visible
                                };
                            }
                            else if (flag == 2)
                            {
                                btnState = new ButtonStateModel()
                                {
                                    BtnOneImage = "Skins/images/flag/OFF.png",
                                    BtnOneVisible = Visibility.Visible,
                                    BtnTwoImage = "Skins/images/flag/OR.png",
                                    BtnTwoVisible = Visibility.Visible
                                }; 
                            }
                        }
                    });
                    return btnState;
        }
        set
        {
            if (value == _buttonStateModel)
            {
                return;
            }
            _buttonStateModel = value;
            RaisePropertyChanged("ButtonStateModel");
        }
    }

现在的问题是，每当我加载 silverlight 应用程序时，UI 上的按钮都无法正确加载其状态。我知道原因是因为GetPR函数来自webservice（asmx），很奇怪我不能在silverlight生成的客户端代码中使用AutoResetEvent进行同步操作：

  public void GetPR(string rtuID, string devID, Action<List<BusControlPR>> action)
    {
        ServiceSoapClient proxy = new ServiceSoapClient();
        proxy.GetPRAsync(rtuID, devID);
        proxy.GetPRCompleted += (sender, args) =>
        {
            //I cannt do Sync Operation Here by using AutoResetEvent.
            if (action != null)
                action(args.Result.ToList());
        };
    }

我正在使用 web 服务（asmx 页面）而不是 WCF ria 服务。 以上问题是我遇到的问题，谁能给我一些启发？

Answer 1

“GetPR”方法仍在异步运行，因此“ButtonStateModel”getter 将立即返回 null（“完成”操作将不起作用）。而且，您不想在 getter 中使用任何类型的阻塞，因为这会阻塞 UI。相反，您应该将“GetPR”放在初始化中，并使用将“ButtonStateModel”属性设置为适当的值：

public class TheViewModel
{
    public ButtonStateModel ButtonStateModel
    {
        get
        {
            return _buttonStateModel;
        }
        set
        {
            if (value == _buttonStateModel)
            {
                return;
            }
            _buttonStateModel = value;
            RaisePropertyChanged("ButtonStateModel");
        }
    }

    public TheViewModel()
    {
        Initialize();
    }

    private void Initialize()
    {
        dataService.GetPR(BusEquipmentPermission.Control.RtuID, BusEquipmentPermission.Control.DevID, (result) =>
        {
            ButtonStateModel btnState = null;
            if (result != null && result.Count > 0)
            {
                var flag = result[0].PRFlag;
                if (flag == 1)
                {
                    btnState = new ButtonStateModel()
                    {
                        BtnOneImage = "Skins/images/flag/OP.png",
                        BtnOneVisible = Visibility.Visible,
                        BtnTwoImage = "Skins/images/flag/OFF.png",
                        BtnTwoVisible = Visibility.Visible
                    };
                }
                else if (flag == 2)
                {
                    btnState = new ButtonStateModel()
                    {
                        BtnOneImage = "Skins/images/flag/OFF.png",
                        BtnOneVisible = Visibility.Visible,
                        BtnTwoImage = "Skins/images/flag/OR.png",
                        BtnTwoVisible = Visibility.Visible
                    }; 
                }
            }
            ButtonStateModel = btnState;
        });
    }
}