How to sync WebService operation in silverlight? - web-services

Question

I am now on a project regarding controlling devices by using silverlight and web service(asmx page). The project flows like below:
pressing the button on the silverlight UI, it will send out a package by using socket to the middlewire. Then middlewire will accept the package and deconstructe it and return back another package to silverlight UI. I am using below code to load the button state, which will trigger database query:
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");
}
}
Now the problem is, whenever I load the silverlight app, the button on the UI can't load its state correctly. I know the reason is because that the GetPR function is from webservice(asmx), it's very oddly that I can't do sync operation by using AutoResetEvent in silverlight generated client code:
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());
};
}
I am using webservice (asmx page) instead of WCF ria service.
Above problem is what i meet, Anyone can give me some light?

Answer 1

The "GetPR" method is still running asynchronously, so the "ButtonStateModel" getter will return null immediately (the "completed" action will then have no effect). And, you do not want to use any kind of blocking inside your getters, as that will block the UI. Instead, you should put the "GetPR" in the initialization, and use the to set the "ButtonStateModel" property to the appropriate value:
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;
});
}
}