Answers

• JohnMiller USForum Administrator, Xamarin Team Xamurai

  October 2016 edited October 2016

  @StephenHauck,

  Have you tried doing your update in Device.BeginInvokeOnMainThread(...)?

  Not MVVM friendly, but we can figure that out if it works.

  0
• StephenHauck USMember ✭✭✭

  October 2016

  John, what do you mean.. I am calling a WCF async web service and subscribing to the complete event.

  I bind to a new instance of the view model in the code behind....

  In the view model constructor I subscribe to the web service complete event and then call the web service.....

  I need a way to let the view know.. "the data has been received and you can rebind"... which I thought was being handled by the databinging in the XAML....

  0
• AdamMeaney USMember ✭✭✭✭✭

  October 2016

  You probably have an error in the bindings, either not using an observable collection as your data source or just something wrong.

  Could you post some code?

  0
• JohnMiller USForum Administrator, Xamarin Team Xamurai

  October 2016

  @StephenHauck,

  Sorry, I was confused. Can you share some code of what you're doing and what type of collection is being used? It would also be good to see the INPC implementation for your backing collection.

  0
• StephenHauck USMember ✭✭✭

  October 2016

  Adam, the fact that I navigate to a modal form and when I come back the data shows kinda rules out binding errors....right?
  How do I log, monitor, capture binding errors?
  The XAML is binding to a List, is this not an observable collection?
  The other thing is that it works from time to time just fine.....

  0
• AdamMeaney USMember ✭✭✭✭✭

  October 2016 Accepted Answer

  The system type List is not an ObservableCollection.

  The object on your ViewModel should be an ObservableCollection if you want collection updates to trickle down to the listview.

  5
• StephenHauck USMember ✭✭✭

  October 2016

  OK, so I changed it and it seems to work but it was working intermittently before .... so I will have to wait and see for sure.
  Could this be because the iOS "emulator" is a simulator and not an emulator ?
  Also, is there a way to trap binding issues / errors?

  0
• JohnMiller USForum Administrator, Xamarin Team Xamurai

  October 2016

  @StephenHauck,

  I don't think the simulator has anything to do with it. My guess is that you were seeing updates if you replaced the entire List<T> instead of adding something to it. Are you adding items to the list now and expecting it to update?

  I ask because that is a difference between using a List<T> and an ObservableCollection<T>. The later will send INPC events when things are added/removed. In contrast, List<T> does not do that. I assumed you had something like

  public List<T> MyItems
  {
     get { return _myItems;}
     set { 
         _myItems = value;
        OnPropertyChanged("MyItems");
     }
  }
  

  If so, the INPC events would have only changed if you did something like

  MyItems = new List<T>(...);

  and not like

  MyItems.Add(...);

  1
• StephenHauck USMember ✭✭✭

  October 2016

  OK, thanks for clarifying that point.
  I was not expecting to see changes in the data I was simply wanting to show the list to allow selections to be made when I experienced the issue but what you are saying about the INPC may have prevented the proper rendering as well??????

  0