Xamarin Forms iOS 切换渲染器空引用异常

Question

我有一个 xamarin 表单开关，当它被切换时，仅在 ios 版本上出现以下异常：

{System.NullReferenceException: Object reference not set to an instance of an object
  at Xamarin.Forms.Platform.iOS.SwitchRenderer.OnElementToggled (System.Object sender, System.EventArgs e) [0x00000] in D:\a\s\Xamarin.Forms.Platform.iOS\Renderers\SwitchRenderer.cs:78 
  at (wrapper delegate-invoke) System.EventHandler`1[Xamarin.Forms.ToggledEventArgs].invoke_void_object_TEventArgs(object,Xamarin.Forms.ToggledEventArgs)
  at Xamarin.Forms.Switch+<>c.<.cctor>b__21_0 (Xamarin.Forms.BindableObject bindable, System.Object oldValue, System.Object newValue) [0x00000] in D:\a\s\Xamarin.Forms.Core\Switch.cs:14 
  at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty property, Xamarin.Forms.BindableObject+BindablePropertyContext context, System.Object value, System.Boolean currentlyApplying, Xamarin.Forms.Internals.SetValueFlags attributes, System.Boolean silent) [0x00120] in D:\a\s\Xamarin.Forms.Core\BindableObject.cs:463 
  at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, Xamarin.Forms.Internals.SetValueFlags attributes, Xamarin.Forms.BindableObject+SetValuePrivateFlags privateAttributes) [0x00173] in D:\a\s\Xamarin.Forms.Core\BindableObject.cs:397 
  at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, Xamarin.Forms.Internals.SetValueFlags attributes) [0x00000] in D:\a\s\Xamarin.Forms.Core\BindableObject.cs:343 
  at Xamarin.Forms.Element.SetValueFromRenderer (Xamarin.Forms.BindableProperty property, System.Object value) [0x00000] in D:\a\s\Xamarin.Forms.Core\Element.cs:250 
  at Xamarin.Forms.Element.Xamarin.Forms.IElementController.SetValueFromRenderer (Xamarin.Forms.BindableProperty property, System.Object value) [0x00000] in D:\a\s\Xamarin.Forms.Core\Element.cs:246 
  at Xamarin.Forms.Platform.iOS.SwitchRenderer.OnControlValueChanged (System.Object sender, System.EventArgs e) [0x00000] in D:\a\s\Xamarin.Forms.Platform.iOS\Renderers\SwitchRenderer.cs:73 
  at UIKit.UIControlEventProxy.Activated () [0x00004] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.18.2.1/src/Xamarin.iOS/UIKit/UIControl.cs:38 
  at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.18.2.1/src/Xamarin.iOS/UIKit/UIApplication.cs:86 
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.18.2.1/src/Xamarin.iOS/UIKit/UIApplication.cs:65 
  at WeCareMobility.iOS.Application.Main (System.String[] args) [0x00002] in /Users/user/Desktop/Vipin/Copiloto/Mobile/WeCareMobility/WeCareMobility.iOS/Main.cs:20 }

Xaml:

<Switch Grid.Row="0" Grid.Column="1" Margin="{OnPlatform Android='0,0,25,0',iOS='0,0,0,8'}" Scale="{OnPlatform iOS= '0.7'}" VerticalOptions="Start" HorizontalOptions="FillAndExpand" IsToggled="False" Toggled="Switch_Toggled" />

CS:

private void Switch_Toggled(object sender, ToggledEventArgs e)
{
            // Perform an action after examining e.Value
            if (e.Value)
            {
                App.Current.MainPage = new NavigationPage(new FlyoutPage());
                _weCareStorageService.SetToggleValue(true);
            }
   }

我没有任何用于切换的渲染器。它适用于 android.
升级到最新的 xamarin forms 稳定版 4.7.0.1080.
使用 VS2019 mac。 iOS SDK version:13.18.2.1 .
清理，重建。 ios 仍然发生崩溃。需要一些帮助...

Answer 1

导航是这样的 issue.Changed 导航：
Device.BeginInvokeOnMainThread(() => { App.Current.MainPage = new NavigationPage(new FlyoutPage()); });
已解决问题。

Xamarin Forms iOS 切换渲染器空引用异常

Xamarin Forms iOS switch renderer null reference exception

xamarin.ios

xamarin.android

xamarin

xamarin.forms