System.ArgumentNullException：MvxWeakEventSubscription 中缺少源事件信息

Question

我们在 Xamarin.IOS 项目中使用 MvvmCross（Hot Tuna 版本）在示例应用“N-39-CrossLight-Touch”中指定数据绑定。

示例应用程序和我们的项目在模拟器（IOS7）上运行良好，但在设备（IOS7）上绑定时抛出以下异常。

System.ArgumentNullException：缺少源事件信息 MvxWeakEventSubscription 参数名称：sourceEventInfo at Cirrious.CrossCore.WeakSubscription.MvxWeakEventSubscription2[System.ComponentModel.INotifyPropertyChanged,System.ComponentModel.PropertyChangedEventArgs]..ctor （INotifyPropertyChanged 源，System.Reflection.EventInfo sourceEventInfo, System.EventHandler1 targetEventHandler) [0x00000] in :0 在 Cirrious.CrossCore.WeakSubscription.MvxNotifyPropertyChangedEventSubscription..ctor （INotifyPropertyChanged 源，System.EventHandler1 targetEventHandler) [0x00000] in :0 at Cirrious.CrossCore.WeakSubscription.MvxWeakSubscriptionExtensionMethods.WeakSubscribe （INotifyPropertyChanged 源，System.EventHandler1 eventHandler） [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Bindings.Source.MvxPropertyInfoSourceBinding..ctor （System.Object 源，System.Reflection.PropertyInfo propertyInfo） [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Bindings.Source.Leaf.MvxLeafPropertyInfoSourceBinding..ctor （System.Object 源，System.Reflection.PropertyInfo propertyInfo） [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Bindings.Source.Leaf.MvxSimpleLeafPropertyInfoSourceBinding..ctor （System.Object 源，System.Reflection.PropertyInfo propertyInfo） [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxPropertySourceBindingFactoryExtension.CreateLeafBinding （System.Object 源， Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken propertyToken) [0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxPropertySourceBindingFactoryExtension.TryCreateBinding （System.Object 源， Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken currentToken，System.Collections.Generic.List1 剩余令牌， IMvxSourceBinding& 结果）[0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.TryCreateBindingFromExtensions （System.Object 源， Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyToken propertyToken，System.Collections.Generic.List1 剩余令牌， IMvxSourceBinding& 结果）[0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.CreateBinding （System.Object 源，IList1 令牌）[0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.Source.Construction.MvxSourceBindingFactory.CreateBinding （System.Object 源，System.String 组合属性名称）[0x00000] 在 :0 在 Cirrious.MvvmCross.Binding.Bindings.SourceSteps.MvxPathSourceStep.OnDataContextChanged () [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Bindings.SourceSteps.MvxSourceStep.set_DataContext （System.Object 值）[0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding.CreateSourceBinding （System.Object 源）[0x00000] in :0 at Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding..ctor (Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest) [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder.BindSingle (Cirrious.MvvmCross.Binding.MvxBindingRequest bindingRequest) [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.Binders.MvxFromTextBinder+c_DisplayClass1.b_0 (Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription 描述）[0x00000] in :0 at System.Linq.Enumerable+c__Iterator102[Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription,Cirrious.MvvmCross.Binding.Bindings.IMvxUpdateableBinding].MoveNext () [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings （IMvxBindingContextOwner 视图，IEnumerable1 绑定，System.Object clearKey) [0x00000] in :0 at Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBindings （IMvxBindingContextOwner 视图，System.Object 目标，IEnumerable1 bindingDescriptions, System.Object clearKey) [0x00000] in :0 at Cirrious.MvvmCross.Binding.BindingContext.MvxBindingContextOwnerExtensions.AddBinding （IMvxBindingContextOwner 视图，System.Object 目标， Cirrious.MvvmCross.Binding.Bindings.MvxBindingDescription bindingDescription, System.Object clearKey) [0x00000] in :0 at Cirrious.MvvmCross.Binding.BindingContext.MvxBaseFluentBindingDescription1[MonoTouch.UIKit.UITextField].Apply () [0x00000] 在 :0 处 Cirrious.MvvmCross.Binding.BindingContext.MvxFluentBindingDescriptionSet2[CrossLightTouch.MyViewController,CrossLightTouch.ViewModels.MyViewModel].Apply () [0x00000] in:0 在 CrossLightTouch.MyViewController.ViewDidLoad () [0x0024f] 在 /Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/MyViewController.cs:81 at at（包装器托管到本机） MonoTouch.ObjCRuntime.Messaging:void_objc_msgSend (intptr,intptr) 在 MonoTouch.UIKit.UIWindow.MakeKeyAndVisible() [0x00008] in /Developer/MonoTouch/Source/monotouch/src/UIKit/.pp-UIWindow.g.cs:129 在 CrossLightTouch.AppDelegate.FinishedLaunching （MonoTouch.UIKit.UIApplication 应用程序，MonoTouch.Foundation.NSDictionary 选项）[0x00042] 在 /Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/AppDelegate.cs:25 at at（包装器托管到本机） MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr) 在 MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] 在 /Developer/MonoTouch/Source/monotouch/src/UIKit/.pp-UIApplication.cs:38 在 CrossLightTouch.Application.Main (System.String[] args) [0x00008] 在 /Users/admin/Downloads/N-39-CrossLight-Touch/CrossLightTouch/Main.cs:17

通过设置 IOS 构建选项 -> Link Behavior -> Don't link ，它可以在设备上正常工作，但二进制大小增加了一倍。

您可以使用“N-39-CrossLight-Touch”示例重现此问题。

是否有解决方法或替代方法？

Answer 1

如果您还没有 LinkerPleaseInclude 文件，请将此处的文件复制到您的项目中：

https://github.com/MvvmCross/MvvmCross/blob/6ab1baa9ca128921208efa994890039edf398474/TestProjects/Android-Support/Fragments/Example.Droid/LinkerPleaseInclude.cs

另外，将以下行添加到Include(TextView text) 方法：

text.AfterTextChanged += (sender, args) => text.Text = "" + text.Text;

如果这不能解决问题，请查找可能在 Mvx 绑定中使用的其他事件并将其添加到 LinkerPleaseInclude 文件中。

此问题是由 Android 上 Mvx 绑定的动态特性引起的。因为绑定是在运行时解析的，所以 Xamarin 链接器认为它们引用的 UI 事件没有被使用，因此它们被从最终生成中删除。在 LinkerPleaseInclude 文件中添加引用会强制包含它们。