Ch19/ConditionalCells/ConditionalCells.iOS: crash when switch "Is Programmer" to ON

[baskren]

Environment:

• MacOSX 10.10.4
• Xamarin Studio 5.9.4 (build 5)
• Xamarin.Forms.1.4.4.6392\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+MonoTouch10+Xamarin.iOS10
• iOS Simulator: iPhone 4s iOS 8.4 (Simulator Version 8.4 (SimulatorApp-565.9 CoreSimulator-117.15))
• XCode: Version 6.4 (6E35b)

Steps to replicate:

• Use source code "as is" from GitHub repository.
• Run (using Debug | iPhone Simulator) using Xamarin Studio and the above environment
• When app launches, tap on the switch in the "Are you a programmer?" cell

Expect to see:

• Switch changes to "ON" and the "Platform" and "Language" cells are enabled

What happens:
App crashes with the following:

• Message: Object reference not set to an instance of an object
• Source: Xamarin.Forms.Platform.iOS
• StackTrace:

  at Xamarin.Forms.Platform.iOS.ViewCellRenderer.UpdateIsEnabled (Xamarin.Forms.Platform.iOS.ViewTableCell cell, Xamarin.Forms.ViewCell viewCell) [0x00007] in <filename unknown>:0 
  at Xamarin.Forms.Platform.iOS.ViewCellRenderer.ViewCellPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs e) [0x0002a] in <filename unknown>:0 
  at (wrapper delegate-invoke) <Module>:invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs)
  at (wrapper delegate-invoke) <Module>:invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs)
  at (wrapper delegate-invoke) <Module>:invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs)
  at (wrapper delegate-invoke) <Module>:invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs)
  at Xamarin.Forms.BindableObject.OnPropertyChanged (System.String propertyName) [0x00012] in <filename unknown>:0 
  at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty property, Xamarin.Forms.BindablePropertyContext context, System.Object value, Boolean currentlyApplying, SetValueFlags attributes, Boolean silent) [0x000ff] in <filename unknown>:0 
  at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, SetValueFlags attributes, SetValuePrivateFlags privateAttributes) [0x00235] in <filename unknown>:0 
  at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, SetValueFlags attributes) [0x00000] in <filename unknown>:0 
  at Xamarin.Forms.BindingExpression.ApplyCore (System.Object sourceObject, Xamarin.Forms.BindableObject target, Xamarin.Forms.BindableProperty property, Boolean fromTarget) [0x001e2] in <filename unknown>:0 
  at Xamarin.Forms.BindingExpression.Apply (Boolean fromTarget) [0x00037] in <filename unknown>:0 
  at Xamarin.Forms.BindingExpression+BindingExpressionPart.<PropertyChanged>b__c () [0x00000] in <filename unknown>:0 
  at Foundation.NSAsyncActionDispatcher.Apply () [0x00000] in /Users/builder/data/lanes/1962/8b265d64/source/maccore/src/Foundation/NSAction.cs:164 
  at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, IntPtr principal, IntPtr delegate) [0x00005] in /Users/builder/data/lanes/1962/8b265d64/source/maccore/src/UIKit/UIApplication.cs:63 
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Users/builder/data/lanes/1962/8b265d64/source/maccore/src/UIKit/UIApplication.cs:47 
  at ConditionalCells.iOS.Application.Main (System.String[] args) [0x00008] in /Users/ben/Downloads/xamarin-forms-book-preview-2-master/Chapter19/ConditionalCells/ConditionalCells/ConditionalCells.iOS/Main.cs:17 

• TargetSite: {Void UpdateIsEnabled(ViewTableCell, Xamarin.Forms.ViewCell)}
• DeclaringType: {Xamarin.Forms.Platform.iOS.ViewCellRenderer}

Notes:

• Switch does work on the Android version