BreezeSharp 实体属性与 Xamarin Forms Entry 绑定答案

【问题标题】：BreezeSharp entity properties binding with Xamarin Forms EntryBreezeSharp 实体属性与 Xamarin Forms Entry 绑定
【发布时间】：2015-01-06 17:00:16
【问题描述】：

我们正在使用 Xamarin Forms 框架开发移动应用程序（目前仅针对 Android）。我们在 MVVMLight 工具包的帮助下构建了我们的应用程序以利用 MVVM 模式。对于数据管理，我们正在使用 BreezeSharp（因为我们已经为 Web 客户端实现了 Breeze 友好的服务器）。

我们正在处理的问题是在绑定到 Breeze 实体属性的 Xamarin Forms Entry 控件中键入时应用程序崩溃。

Xaml 视图中的入口控件：

<Entry Text="{Binding SelectedCustomerAddress.AddressLine1}" />

ViewModel 中的属性（Set() 来自 MVVMLight ViewModelBase）：

public CustomerAddress SelectedCustomerAddress
{
    get { return this.selectedCustomerAddress; }
    set { this.Set(() => this.SelectedCustomerAddress, ref this.selectedCustomerAddress, value);}
}

Breeze CLR 类型中的属性：

public string AddressLine1
{
    get { return this.GetValue<string>(); }
    set { this.SetValue(value); }
}

在输入字段中仅输入几个字符后，应用程序会因堆栈跟踪而崩溃：

11-10 11:51:02.896 F/        ( 4924): * Assertion at /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/mono/mono/metadata/sgen-stw.c:68, condition `info->stack_start >= info->stack_start_limit && info->stack_start < info->stack_end' not met
11-10 11:51:02.900 E/mono-rt ( 4924): Stacktrace:
11-10 11:51:02.900 E/mono-rt ( 4924): 
11-10 11:51:02.904 E/mono-rt ( 4924):   at <unknown> <0xffffffff>
11-10 11:51:02.908 E/mono-rt ( 4924):   at (wrapper managed-to-native) object.MemberwiseClone (object) <IL 0x0002d, 0xffffffff>
11-10 11:51:02.912 E/mono-rt ( 4924):   at System.Delegate.Clone () <IL 0x00001, 0x00027>
11-10 11:51:02.916 E/mono-rt ( 4924):   at System.MulticastDelegate.CombineImpl (System.Delegate) <IL 0x000be, 0x0037c>
11-10 11:51:02.916 E/mono-rt ( 4924):   at System.Delegate.Combine (System.Delegate,System.Delegate) <IL 0x00062, 0x001f8>
11-10 11:51:02.920 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.add_EntityPropertyChanged (System.ComponentModel.PropertyChangedEventHandler) <IL 0x0000b, 0x00057>
11-10 11:51:02.924 E/mono-rt ( 4924):   at Breeze.Sharp.BaseEntity.System.ComponentModel.INotifyPropertyChanged.add_PropertyChanged (System.ComponentModel.PropertyChangedEventHandler) [0x00000] in c:\GitHub\breeze.sharp\Breeze.Sharp\BaseEntity.cs:74
11-10 11:51:02.928 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression.ApplyCore (object,Xamarin.Forms.BindableObject,Xamarin.Forms.BindableProperty,bool) <IL 0x00130, 0x0077f>
11-10 11:51:02.928 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression.Apply (bool) <IL 0x00041, 0x000f3>
11-10 11:51:02.932 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression/BindingExpressionPart.<PropertyChanged>b__12 () <IL 0x00007, 0x0002f>
11-10 11:51:02.932 E/mono-rt ( 4924):   at Java.Lang.Thread/RunnableImplementor.Run () [0x0000b] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/src/Java.Lang/Thread.cs:36
11-10 11:51:02.932 E/mono-rt ( 4924):   at Java.Lang.IRunnableInvoker.n_Run (intptr,intptr) [0x00009] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/platforms/android-18/src/generated/Java.Lang.IRunnable.cs:71
11-10 11:51:02.932 E/mono-rt ( 4924):   at (wrapper dynamic-method) object.39beb2b5-65b4-431f-a21a-3e626049fa1f (intptr,intptr) <IL 0x00011, 0x0001b>
11-10 11:51:02.932 E/mono-rt ( 4924):   at (wrapper native-to-managed) object.39beb2b5-65b4-431f-a21a-3e626049fa1f (intptr,intptr) <IL 0x00022, 0xffffffff>
11-10 11:51:02.936 E/mono-rt ( 4924):   at <unknown> <0xffffffff>
11-10 11:51:02.936 E/mono-rt ( 4924):   at (wrapper managed-to-native) object.wrapper_native_0xb60a0eb0 (intptr,intptr,intptr,Android.Runtime.JValue[]) <IL 0x00120, 0xffffffff>
11-10 11:51:02.936 E/mono-rt ( 4924):   at Android.Runtime.JNIEnv.CallVoidMethod (intptr,intptr,Android.Runtime.JValue[]) [0x00040] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:504
11-10 11:51:02.940 E/mono-rt ( 4924):   at Android.App.Activity.RunOnUiThread (Java.Lang.IRunnable) [0x0002d] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/platforms/android-18/src/generated/Android.App.Activity.cs:4130
11-10 11:51:02.940 E/mono-rt ( 4924):   at Android.App.Activity.RunOnUiThread (System.Action) [0x00000] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/src/Android.App/Activity.cs:23
11-10 11:51:02.940 E/mono-rt ( 4924):   at Xamarin.Forms.Forms/AndroidPlatformServices.BeginInvokeOnMainThread (System.Action) <IL 0x0000b, 0x00053>
11-10 11:51:02.940 E/mono-rt ( 4924):   at Xamarin.Forms.Device.BeginInvokeOnMainThread (System.Action) <IL 0x00006, 0x00038>
11-10 11:51:02.940 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression/BindingExpressionPart.PropertyChanged (object,System.ComponentModel.PropertyChangedEventArgs) <IL 0x00087, 0x00313>
11-10 11:51:02.944 E/mono-rt ( 4924):   at (wrapper delegate-invoke) <Module>.invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs) <IL 0x00027, 0x00042>
11-10 11:51:02.944 E/mono-rt ( 4924):   at (wrapper delegate-invoke) <Module>.invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs) <IL 0x00027, 0x00042>
11-10 11:51:02.944 E/mono-rt ( 4924):   at (wrapper delegate-invoke) <Module>.invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs) <IL 0x00027, 0x00042>

..... (2500 lines)

11-10 11:51:03.564 E/mono-rt ( 4924):   at (wrapper delegate-invoke) <Module>.invoke_void_object_PropertyChangedEventArgs (object,System.ComponentModel.PropertyChangedEventArgs) <IL 0x00059, 0xffffffff>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.OnPropertyChangedCore (System.ComponentModel.PropertyChangedEventArgs) [0x0000b] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:1315
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect/<>c__DisplayClass4b.<OnPropertyChanged>b__4a () [0x00000] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:1306
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.QueueEvent (System.Action) [0x0003e] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:1362
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.OnPropertyChanged (System.ComponentModel.PropertyChangedEventArgs) [0x0003f] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:1305
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.SetValueWithEvents<T> (T,object,System.Action`3<T, object, object>) [0x00042] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:563
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.SetDpValue (Breeze.Sharp.DataProperty,object) [0x00000] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:529
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.SetValue (Breeze.Sharp.StructuralProperty,object) [0x00052] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:522
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.EntityAspect.SetValue (string,object) [0x00031] in c:\GitHub\breeze.sharp\Breeze.Sharp\EntityAspect.cs:507
11-10 11:51:03.564 E/mono-rt ( 4924):   at Breeze.Sharp.BaseEntity.SetValue (object,string) [0x00000] in c:\GitHub\breeze.sharp\Breeze.Sharp\BaseEntity.cs:37
11-10 11:51:03.564 E/mono-rt ( 4924):   at Client.Common.Model.Proxy.CustomerAddress.set_AddressLine2 (string) [0x00001] in c:\Projects\Client\source\Client.Common\Model\Proxy\CustomerAddress.cs:26
11-10 11:51:03.564 E/mono-rt ( 4924):   at (wrapper runtime-invoke) <Module>.runtime_invoke_void__this___object (object,intptr,intptr,intptr) <IL 0x00052, 0xffffffff>
11-10 11:51:03.564 E/mono-rt ( 4924):   at <unknown> <0xffffffff>
11-10 11:51:03.564 E/mono-rt ( 4924):   at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&) <IL 0x00030, 0xffffffff>
11-10 11:51:03.564 E/mono-rt ( 4924):   at System.Reflection.MonoMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <IL 0x0004a, 0x0016f>
11-10 11:51:03.564 E/mono-rt ( 4924):   at System.Reflection.MethodBase.Invoke (object,object[]) <IL 0x00006, 0x0004b>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression.ApplyCore (object,Xamarin.Forms.BindableObject,Xamarin.Forms.BindableProperty,bool) <IL 0x002f4, 0x00fd3>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.BindingExpression.Apply (bool) <IL 0x00041, 0x000f3>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.Binding.Apply (bool) <IL 0x00027, 0x000db>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty,object,bool,bool,bool) <IL 0x00090, 0x00295>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty,object,bool,bool,bool) <IL 0x00213, 0x007b7>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Xamarin.Forms.Platform.Android.EntryRenderer.Android.Text.ITextWatcher.OnTextChanged (Java.Lang.ICharSequence,int,int,int) <IL 0x00014, 0x00087>
11-10 11:51:03.564 E/mono-rt ( 4924):   at Android.Text.ITextWatcherInvoker.n_OnTextChanged_Ljava_lang_CharSequence_III (intptr,intptr,intptr,int,int,int) [0x00011] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.18-series/3b7ef0a7/source/monodroid/src/Mono.Android/platforms/android-18/src/generated/Android.Text.ITextWatcher.cs:149
11-10 11:51:03.564 E/mono-rt ( 4924):   at (wrapper dynamic-method) object.369fe85e-8bc0-4aec-88da-b1540ec93f9c (intptr,intptr,intptr,int,int,int) <IL 0x00029, 0x0003f>
11-10 11:51:03.564 E/mono-rt ( 4924):   at (wrapper native-to-managed) object.369fe85e-8bc0-4aec-88da-b1540ec93f9c (intptr,intptr,intptr,int,int,int) <IL 0x00028, 0xffffffff>
11-10 11:51:03.564 E/mono-rt ( 4924): 
11-10 11:51:03.564 E/mono-rt ( 4924): =================================================================
11-10 11:51:03.564 E/mono-rt ( 4924): Got a SIGSEGV while executing native code. This usually indicates
11-10 11:51:03.564 E/mono-rt ( 4924): a fatal error in the mono runtime or one of the native libraries 
11-10 11:51:03.564 E/mono-rt ( 4924): used by your application.
11-10 11:51:03.564 E/mono-rt ( 4924): =================================================================
11-10 11:51:03.564 E/mono-rt ( 4924): 
11-10 11:51:03.564 F/libc    ( 4924): Fatal signal 11 (SIGSEGV) at 0xdeadbaad (code=1), thread 4924 (r.nimbus.mobile)
The program 'Mono' has exited with code 0 (0x0).

在我看来，触发了很多事件，导致事件堆栈溢出。

绑定到非 Breeze 属性时，条目工作正常。绑定到分离实体时也可以正常工作。

在深入研究 Breeze EntityAspect.cs 代码后，我发现一切都来自这个函数：

internal void OnPropertyChanged(PropertyChangedEventArgs pcArgs)
    {
      if (this.IsDetached || !this.EntityGroup.ChangeNotificationEnabled)
        return;
      pcArgs = pcArgs ?? EntityAspect.AllPropertiesChangedEventArgs;
      this.QueueEvent((Action) (() =>
      {
        this.OnPropertyChangedCore(pcArgs);
        this.OnEntityChangedCore(EntityAction.PropertyChange, (EventArgs) pcArgs);
      }));
    }

所以我在 Breeze 中使用以下方法禁用了引发事件：

this.EntityManager.ChangeNotificationEnabled = false;

这似乎解决了我们的条目绑定问题，但我们不确定这是否为其他问题打开了大门。

这种方法的后果是什么？

这些 EntityPropertyChanged 和 PropertyChanged 事件是由 Breeze 代码使用还是仅用于我们的代码附加到它们上？

或者您是否看到了解决此问题的其他方法？

更新：后果是：如果我们在 UI 上将多个元素绑定到同一个属性，并且如果我们在一个地方更新该属性，则更改在其他地方不可见。

示例：从 ListView 中选择元素并将所选元素绑定到某些条目字段（在 ListView 之外）。当我们通过该输入字段更新元素时，更改在 ListView 上不可见（因为未通知 ListView）。

启用 Breeze PropertyChanged 机制（EntityPropertyChanged 和 ForceEntityPropertyChanged）后，这将开箱即用，但正如我上面提到的，应用程序崩溃存在问题。

我们最终在我们的基础实体（继承自 Breeze BaseEntity）中实现了 OnPropertyChanged 和 RaisePropertyChanged 方法。这种技术类似于 ObservableObject 的 MVVMLight 实现。

这段代码运行良好（没有应用程序崩溃）：

public bool IsImportant
{
    get { return this.GetValue<bool>(); }
    set
    {
        this.SetValue(value); 
        this.OnPropertyChanged();
    }
}

我们还可以在需要时调用 RaisePropertyChanged：

this.SelectedNote.RaisePropertyChanged("IsImportant");

【问题讨论】：

标签： mvvm-light xamarin.forms breeze-sharp

【解决方案1】：

我猜有一种方法可以修改绑定，使其仅在用户完成文本编辑后触发，而不是每次更改字符。这对于您要通过应用程序完成的工作是否足够？在 WPF/Silverlight XAML 中，绑定上有一个名为 UpdateSourceTrigger 的属性，您可以设置该属性以指示在哪个点推送更改。我正在联系 Xamarin 以了解他们是否具有同等属性。

【讨论】：

Xamarin 表单 Entry/Editor 具有 Completed 事件，该事件在输入文本后触发（或者更准确地说是在取消聚焦元素时）。这种方法的问题在于，我们需要在后面的代码中为每个条目字段编写事件处理程序，而不是使用双向绑定。

【解决方案2】：

未测试，但您可以在 EntityManager 上禁用属性通知，因此您可以按需切换此属性。

【讨论】：