Calculated Properties

0. Install Ditto.AsyncMvvm.Calculated.

1. Derive your view model from CalculatedAsyncBindableBase:

   using Ditto.AsyncMvvm.Calculated;
   
   class UniversalAnswerViewModel : CalculatedAsyncBindableBase
   {
   }

2. Implement the asynchronous method for calculating the value of the trigger property:

       private async Task<int?> GetAnswerAsync()
       {
           await Task.Delay(TimeSpan.FromDays(7500000 * 365.25));
           return 42;
       }

3. Define the trigger property:

       public int? Answer
       {
           get { return Property.Get(GetAnswerAsync); }
       }

4. Define the calculated property:

       public string AnswerString
       {
           get
           {
               return Property.Calculated(() => Answer.HasValue ? Answer.Value.ToString() : null);
           }
       }

Calculated Properties Copyright (c) 2014 StephenCleary