c# - MvvmCross - 在 UISlider 中处理绑定(bind)时获取 TargetInvocationException 和 SIGABRT

Question

我正在使用 Xamarin.iOS 和 MvvmCross (v5.6.3) 开发一个项目，我在一个 View Controller 上有一个非常典型的 UISlider，其值绑定(bind)到其 View 上的 float 属性-模型。

set.Bind(MySlider).For(x => x.Value).To(vm => vm.FloatProperty).TwoWay();

当 View 卸载并尝试处理现有的绑定(bind)时(比如导航到另一个 View 模型时)，我收到以下未处理的异常和 SIGABRT:

Unhandled Exception:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> UIKit.UIKitThreadAccessException: UIKit Consistency error: you are calling a UIKit method that can only be invoked from the UI thread.
  at UIKit.UIApplication.EnsureUIThread () [0x00023] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIApplication.cs:88 
  at UIKit.UIControl.RemoveTarget (Foundation.NSObject target, System.IntPtr sel, UIKit.UIControlEvent events) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.g.cs:235 
  at UIKit.UIControl.RemoveTarget (System.EventHandler notification, UIKit.UIControlEvent events) [0x00057] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.cs:116 
  at UIKit.UIControl.remove_ValueChanged (System.EventHandler value) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.cs:209 
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke(System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00032] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/MonoMethod.cs:305 
   --- End of inner exception stack trace ---
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00046] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/MonoMethod.cs:313 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/reflection/methodbase.cs:229 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].RemoveEventHandler () [0x00024] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].Dispose (System.Boolean disposing) [0x00003] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].Dispose () [0x00000] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Binding.iOS.Target.MvxUISliderValueTargetBinding.Dispose (System.Boolean isDisposing) [0x0001b] in <614c9ef828c14ba687a40ec2656f480f>:0 
  at MvvmCross.Binding.Bindings.MvxBinding.Finalize () [0x00000] in <866b1e46764b48aab0d408952a6f006f>:0 
2018-04-09 23:15:20.210 MyProject.iOS[73770:3302608] Unhandled managed exception:
Exception has been thrown by the target of an invocation. (System.Reflection.TargetInvocationException)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00046] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/MonoMethod.cs:313 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/reflection/methodbase.cs:229 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].RemoveEventHandler () [0x00024] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].Dispose (System.Boolean disposing) [0x00003] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Platform.WeakSubscription.MvxWeakEventSubscription`1[TSource].Dispose () [0x00000] in <6adc0d5857264558a9d45778a78ae02a>:0 
  at MvvmCross.Binding.iOS.Target.MvxUISliderValueTargetBinding.Dispose (System.Boolean isDisposing) [0x0001b] in <614c9ef828c14ba687a40ec2656f480f>:0 
  at MvvmCross.Binding.Bindings.MvxBinding.Finalize () [0x00000] in <866b1e46764b48aab0d408952a6f006f>:0 
 --- inner exception ---
UIKit Consistency error: you are calling a UIKit method that can only be invoked from the UI thread. (UIKit.UIKitThreadAccessException)
  at UIKit.UIApplication.EnsureUIThread () [0x00023] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIApplication.cs:88 
  at UIKit.UIControl.RemoveTarget (Foundation.NSObject target, System.IntPtr sel, UIKit.UIControlEvent events) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.g.cs:235 
  at UIKit.UIControl.RemoveTarget (System.EventHandler notification, UIKit.UIControlEvent events) [0x00057] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.cs:116 
  at UIKit.UIControl.remove_ValueChanged (System.EventHandler value) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/UIKit/UIControl.cs:209 
  at (wrapper managed-to-native) System.Reflection.MonoMethod.InternalInvoke(System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00032] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.9.1.24/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/MonoMethod.cs:305 
2018-04-09 23:15:20.210 MyProject.iOS[73770:3302608] critical: Stacktrace:

2018-04-09 23:15:20.211 MyProject.iOS[73770:3302608] critical: 
Native stacktrace:

2018-04-09 23:15:20.212 MyProject.iOS[73770:3302608] critical:  0   MyProject.iOS                       0x00000001038b4574 mono_handle_native_crash + 244
2018-04-09 23:15:20.212 MyProject.iOS[73770:3302608] critical:  1   libsystem_platform.dylib            0x000000010bbecf5a _sigtramp + 26
2018-04-09 23:15:20.213 MyProject.iOS[73770:3302608] critical:  2   ???                                 0x0000000103dd308a 0x0 + 4359794826
2018-04-09 23:15:20.213 MyProject.iOS[73770:3302608] critical:  3   libsystem_c.dylib                   0x000000010b8820eb abort + 127
2018-04-09 23:15:20.213 MyProject.iOS[73770:3302608] critical:  4   MyProject.iOS                       0x0000000103a5b2df xamarin_unhandled_exception_handler + 47
2018-04-09 23:15:20.214 MyProject.iOS[73770:3302608] critical:  5   MyProject.iOS                       0x000000010391b854 mono_invoke_unhandled_exception_hook + 148
2018-04-09 23:15:20.214 MyProject.iOS[73770:3302608] critical:  6   MyProject.iOS                       0x00000001039c2a3e mono_thread_internal_unhandled_exception + 110
2018-04-09 23:15:20.215 MyProject.iOS[73770:3302608] critical:  7   MyProject.iOS                       0x000000010391d15a mono_gc_run_finalize + 842
2018-04-09 23:15:20.215 MyProject.iOS[73770:3302608] critical:  8   MyProject.iOS                       0x00000001039fc9ba sgen_gc_invoke_finalizers + 234
2018-04-09 23:15:20.215 MyProject.iOS[73770:3302608] critical:  9   MyProject.iOS                       0x000000010391eae4 finalizer_thread + 756
2018-04-09 23:15:20.215 MyProject.iOS[73770:3302608] critical:  10  MyProject.iOS                       0x00000001039c3600 start_wrapper + 704
2018-04-09 23:15:20.215 MyProject.iOS[73770:3302608] critical:  11  libsystem_pthread.dylib             0x000000010bbfe6c1 _pthread_body + 340
2018-04-09 23:15:20.216 MyProject.iOS[73770:3302608] critical:  12  libsystem_pthread.dylib             0x000000010bbfe56d _pthread_body + 0
2018-04-09 23:15:20.216 MyProject.iOS[73770:3302608] critical:  13  libsystem_pthread.dylib             0x000000010bbfdc5d thread_start + 13
2018-04-09 23:15:20.216 MyProject.iOS[73770:3302608] critical: 
=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

绑定(bind)工作正常，只有当我尝试导航到另一个 View 模型 正在卸载 View 时才会发生这种情况。

我错过了什么吗？或者这可能是 MvvmCross 上的错误？

编辑: 最后检查了卸载 View 时是否会出现此问题，无论我是否导航到另一个 View 模型。我删除了指向导航问题的引用。

Answer 1

目前 MvvmCross 5.x.x 中存在一个关于 UISlider 的错误。 PR 2750 已解决此问题它将在 6.0.0 版本中发布

与此同时，您应该能够覆盖绑定(bind)以通过使用修复创建自定义绑定(bind)来为您的项目修复它。问题在 Dispose .

public class FixedMvxUISliderValueTargetBinding : MvxPropertyInfoTargetBinding<UISlider>
{
    private IDisposable _subscription;

    public FixedMvxUISliderValueTargetBinding(object target, PropertyInfo targetPropertyInfo) 
        : base(target, targetPropertyInfo) { }

    protected override void SetValueImpl(object target, object value)
    {
        var view = target as UISlider;
        if (view == null) return;
        view.Value = (float)value;
    }

    private void HandleSliderValueChanged(object sender, EventArgs e)
    {
        var view = View;
        if (view == null) return;
        FireValueChanged(view.Value);
    }

    public override MvxBindingMode DefaultMode => MvxBindingMode.TwoWay;

    public override void SubscribeToEvents()
    {
        var slider = View;
        if (slider == null)
        {
            MvxBindingTrace.Trace(
                MvxTraceLevel.Error, 
                "Error - UISlider is null in MvxUISliderValueTargetBinding");
            return;
        }
        _subscription = slider.WeakSubscribe(
            nameof(slider.ValueChanged), 
            HandleSliderValueChanged);
    }

    protected override void Dispose(bool isDisposing)
    {
        base.Dispose(isDisposing);
        if (isDisposing)
        {
            _subscription?.Dispose();
            _subscription = null;
        }
    }
}

然后在您的 Setup.cs 中注册绑定(bind)。请注意，确保先调用 base.FillTargetFactories。

protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
{
    base.FillTargetFactories(registry);
    registry.RegisterPropertyInfoBindingFactory(
        typeof(FixedMvxUISliderValueTargetBinding),
        typeof(UISlider),
        nameof(UISlider.Value));
}