title: Xamarin Forms - picker selectedItem not firing
body: <p>The following example works fine (<a href="https://developer.xamarin.com/samples/xamarin-forms/UserInterface/BindablePicker/" rel="nofollow noreferrer">https://developer.xamarin.com/samples/xamarin-forms/UserInterface/BindablePicker/</a>)</p>
  
  <p>When i try to implement it in my code, the object referenced for selectedItem is not being set. The picker is loading and selecting data fine, just not updating the object.</p>
  
  <p>Here is some of the code i'm using:
  XAML Page</p>
  
  <pre><code> &lt;Picker x:Name="testpicker" Title="Select a Service" ItemsSource="{Binding Services}, Mode=TwoWay}" ItemDisplayBinding="{Binding ServiceDescription}" SelectedItem="{Binding SelectedServiceName, Mode=TwoWay}" /&gt;
  </code></pre>
  
  <p>I have the object in the view model, but this is never called when the picker items are selected.:</p>
  
  <pre><code>string selectedServiceName;
      public string SelectedServiceName
      {
          get { return selectedServiceName; }
          set
          {
              if (selectedServiceName != value)
              {
                  selectedServiceName = value;
                  PickerOnPropertyChanged();
                  PickerOnPropertyChanged("SelectedService");
              }
          }
      }
  </code></pre>
  
  <p>The binding is done from the controller when the view loads by the way....</p>
  
  <pre><code>  protected async override void OnAppearing()
      {
  
          base.OnAppearing();
          await viewModel.LoadPreferenceData();
          await viewModel.LoadServiceData();
  
          testpicker.SelectedIndex = 5;
  
      }
  </code></pre>
  
  <p>I've also updated the base class to reflect the tutorial, i've changed the names.</p>
  
  <p>Can you see anything obvious why this is not working? I'm happy to supply more code if needed.</p>