我正在使用Xamarin.iOS和MvvmCross（v5.6.3）开展项目，我在一个视图控制器上有一个非常典型的UISlider，其值在其视图中绑定到float属性 - 模型。
set.Bind(MySlider).For(x => x.Value).To(vm => vm.FloatProperty).TwoWay();
当视图卸载并尝试处理现有绑定时（例如导航到另一个视图模型时）我使用SIGABRT得到以下未处理的异常：
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.
=================================================================
绑定工作正常，只有当我尝试导航到另一个视图模型 正在卸载视图时才会发生这种情况。
我错过了什么吗？或者这可能是MvvmCross上的一个错误？
修改 最后检查在卸载视图时发生此问题，无论我是否导航到另一个视图模型。我已删除了我指向导航问题的参考文献。
答案 0 :(得分：3)
MvvmCross 5.x.x目前存在与UISlider相关的错误。该问题已通过PR 2750修复，该版本将在6.0.0版本中发布
与此同时，您应该能够通过使用修复程序创建自定义绑定来覆盖绑定以修复项目。问题出在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Setup.cs注册绑定。请注意，请务必先拨打base.FillTargetFactories。
protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
{
base.FillTargetFactories(registry);
registry.RegisterPropertyInfoBindingFactory(
typeof(FixedMvxUISliderValueTargetBinding),
typeof(UISlider),
nameof(UISlider.Value));
}
答案 1 :(得分：1)
您正在调用只能从UI线程调用的UIKit方法。
尝试在UIThread中调用导航方法。
this.InvokeOnMainThread(async () =>
{
//navigate
});
如果以上操作不起作用，您可以尝试关闭UI线程检查。
var previous = UIApplication.CheckForIllegalCrossThreadCalls;
UIApplication.CheckForIllegalCrossThreadCalls = false;
//navigate
UIApplication.CheckForIllegalCrossThreadCalls = previous;