awcullen
commented
7 years ago The short answer is that the ViewModel is not initially connected to the server when it is constructed. Connecting and subscribing happens asynchronously on a threadpool thread. If you wish to read the value of Axis1 in a method, then you could
private static async Task<double> GetValueAsync()
{
var channel = await UaApplication.Current.GetChannelAsync("opc.tcp://localhost:26543");
var result = await channel.ReadAsync(new ReadRequest
{
NodesToRead = new[] {
new ReadValueId { NodeId = NodeId.Parse("ns=2;s=Robot1_Axis1"), AttributeId = AttributeIds.Value }
}
});
double axisdata = result.Results[0].GetValueOrDefault<float>();
return axisdata;
}
The long answer is that initially SubscriptionBase is monitoring for when a view adds a eventhandler to PropertyChanged event. When a view adds an eventhandler, then SubscriptionBase creates the subscription. When the view removes the eventhandler, then SubscriptionBase deletes the subscription. So if you are creating a viewmodel, but not using a view (with bindings to the viewmodel), then you must add an eventhandler yourself if you want the SubscriptionBase to work.
var vm= new MainPageViewModel();
var d = new PropertyChangedEventHandler((s, e) => { });
// create the subscription.
vm.PropertyChanged += d;
// and when you want the subscription deleted.
sub.PropertyChanged -= d;
tejasklodha
Dear Sir,
I can able to fetch live data via viewmodel. But how can I fetch live data through method which call to Viewmodel from diffrent class
Example
I have one main view model MainPageViewModel
Now I want Live data through method GetData() as below from different class
But every time I got value 0 from above method. Any mistake i Did in above?
need your help.
thanks,