System.ArgumentNullException: missing source event info in MvxWeakEventSubscription - xamarin.ios

Question

We are using data binding in our Xamarin.IOS project using MvvmCross(Hot Tuna version) as specified in the sample app “N-39-CrossLight-Touch”.
The sample app as well as our project works fine on simulator(IOS7) but on device(IOS7) it throws the below exception while binding.
System.ArgumentNullException: missing source event info in
MvxWeakEventSubscription Parameter name: sourceEventInfo at
Cirrious.CrossCore.WeakSubscription.MvxWeakEventSubscription2[System.ComponentModel.INotifyPropertyChanged,System.ComponentModel.PropertyChangedEventArgs]..ctor
(INotifyPropertyChanged source, System.Reflection.EventInfo
sourceEventInfo, System.EventHandler1 targetEventHandler) [0x00000] in
:0 at
Cirrious.CrossCore.WeakSubscription.MvxNotifyPropertyChangedEventSubscription..ctor
(INotifyPropertyChanged source, System.EventHandler1
targetEventHandler) [0x00000] in :0 at
Cirrious.CrossCore.WeakSubscription.MvxWeakSubscriptionExtensionMethods.WeakSubscribe
(INotifyPropertyChanged source, System.EventHandler1 eventHandler)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.MvxPropertyInfoSourceBinding..ctor
(System.Object source, System.Reflection.PropertyInfo propertyInfo)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Leaf.MvxLeafPropertyInfoSourceBinding..ctor
(System.Object source, System.Reflection.PropertyInfo propertyInfo)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Leaf.MvxSimpleLeafPropertyInfoSourceBinding..ctor
(System.Object source, System.Reflection.PropertyInfo propertyInfo)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxPropertySourceBindingFactoryExtension.CreateLeafBinding
(System.Object source,
Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken
propertyToken) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxPropertySourceBindingFactoryExtension.TryCreateBinding
(System.Object source,
Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken
currentToken, System.Collections.Generic.List1 remainingTokens,
IMvxSourceBinding& result) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.TryCreateBindingFromExtensions
(System.Object source,
Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken
propertyToken, System.Collections.Generic.List1 remainingTokens,
IMvxSourceBinding& result) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.CreateBinding
(System.Object source, IList1 tokens) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.CreateBinding
(System.Object source, System.String combinedPropertyName) [0x00000]
in :0 at
Cirrious.MvvmCross.Binding.Bindings.SourceSteps.MvxPathSourceStep.OnDataContextChanged
() [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.SourceSteps.MvxSourceStep.set_DataContext
(System.Object value) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding.CreateSourceBinding
(System.Object source) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding..ctor
(Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder.BindSingle
(Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest)
[0x00000] in :0 at
Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder+<>c_DisplayClass1.b_0
(Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription
description) [0x00000] in :0 at
System.Linq.Enumerable+c__Iterator102[Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription,Cirrious.MvvmCross.Binding.Bindings.IMvxUpdateableBinding].MoveNext
() [0x00000] in :0 at
Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings
(IMvxBindingContextOwner view, IEnumerable1 bindings, System.Object
clearKey) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings
(IMvxBindingContextOwner view, System.Object target, IEnumerable1
bindingDescriptions, System.Object clearKey) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBinding
(IMvxBindingContextOwner view, System.Object target,
Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription
bindingDescription, System.Object clearKey) [0x00000] in :0 at
Cirrious.MvvmCross.Binding.BindingContext.MvxBaseFluentBindingDescription1[MonoTouch.UIKit.UITextField].Apply
() [0x00000] in :0 at
Cirrious.MvvmCross.Binding.BindingContext.MvxFluentBindingDescriptionSet2[CrossLightTouch.MyViewController,CrossLightTouch.ViewModels.MyViewModel].Apply
() [0x00000] in :0 at CrossLightTouch.MyViewController.ViewDidLoad ()
[0x0024f] in
/Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/MyViewController.cs:81
at at (wrapper managed-to-native)
MonoTouch.ObjCRuntime.Messaging:void_objc_msgSend (intptr,intptr) at
MonoTouch.UIKit.UIWindow.MakeKeyAndVisible () [0x00008] in
/Developer/MonoTouch/Source/monotouch/src/UIKit/.pp-UIWindow.g.cs:129
at CrossLightTouch.AppDelegate.FinishedLaunching
(MonoTouch.UIKit.UIApplication app, MonoTouch.Foundation.NSDictionary
options) [0x00042] in
/Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/AppDelegate.cs:25
at at (wrapper managed-to-native)
MonoTouch.UIKit.UIApplication:UIApplicationMain
(int,string[],intptr,intptr) at MonoTouch.UIKit.UIApplication.Main
(System.String[] args, System.String principalClassName, System.String
delegateClassName) [0x0004c] in
/Developer/MonoTouch/Source/monotouch/src/UIKit/.pp-UIApplication.cs:38
at CrossLightTouch.Application.Main (System.String[] args) [0x00008]
in
/Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/Main.cs:17
By setting the IOS build options -> Link Behavior -> Don’t link , it works on device as expected, but the binary size has been doubled.
You can reproduce this issue with “N-39-CrossLight-Touch” sample.
Is there a fix or alternative for this?

Answer 1

If you don't already have a LinkerPleaseInclude file, copy the one from here into your project:
https://github.com/MvvmCross/MvvmCross/blob/6ab1baa9ca128921208efa994890039edf398474/TestProjects/Android-Support/Fragments/Example.Droid/LinkerPleaseInclude.cs
Also, add the following line to the Include(TextView text) method:
text.AfterTextChanged += (sender, args) => text.Text = "" + text.Text;
If that doesn't solve it, look for other events that may be used in the Mvx bindings and add those to the LinkerPleaseInclude file.
This issue is caused by the dynamic nature of Mvx binding on Android. Because the bindings are resolved at runtime, the Xamarin linker thinks the UI events they reference are not being used so they are removed from the final build. Adding references in the LinkerPleaseInclude file forces them to be included.