Xamarin.Forms-爲什麼CustomRenderer Android for NavigationPage引發InvalidCastException？

我嘗試在NavigationBar上爲Xamarin.Forms android build設置背景圖像。這裏的例子幾乎相同。我使用了這個自定義渲染器;Xamarin.Forms-爲什麼CustomRenderer Android for NavigationPage引發InvalidCastException？

[assembly: ExportRenderer(typeof(NavigationPage), typeof(CustomNavigationRenderer))] 
namespace xfprism.Droid 
{ 

    public class CustomNavigationRenderer : NavigationRenderer 
    { 
     protected override void OnElementChanged(ElementChangedEventArgs<NavigationPage> e) 
     { 
      base.OnElementChanged(e); 

      ExtendedActionBar(); 
     } 

     void ExtendedActionBar() 
     { 
      var actionBar = ((Activity)Context).ActionBar; 
      actionBar.SetIcon(Resources.GetDrawable(Resource.Drawable.icon)); 
      actionBar.SetBackgroundDrawable(Resources.GetDrawable(Resource.Drawable.coffee)); 
     } 
    } 
}

而我的app.xaml.cs;

public partial class App 
{ 
    protected override void OnInitialized() 
    { 
     InitializeComponent(); 
     MainPage = new NavigationPage(new MainPage()); 
    } 
}

但是，當我嘗試調試項目我上線base.OnElementChanged(e); InvalidCastException的。有什麼我失蹤？

FYI：我使用Xamarin 4.1.0.462

的Visual Studio 2015年更新2

編輯：

這裏是調用堆棧;

>0xBE in Xamarin.Forms.Platform.Android.NavigationRenderer.SwitchContentAsync at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Renderers\NavigationRenderer.cs:196,4 
0x4 in Xamarin.Forms.Platform.Android.NavigationRenderer.OnPushAsync at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Renderers\NavigationRenderer.cs:124,4  
0x3 in Xamarin.Forms.Platform.Android.NavigationRenderer.PushViewAsync at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Renderers\NavigationRenderer.cs:34,4 
0x3 in Xamarin.Forms.Platform.Android.NavigationRenderer.<OnElementChanged>b__9_0 at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Renderers\NavigationRenderer.cs:97,41 
0x12 in Xamarin.Forms.EnumerableExtensions.ForEach<Xamarin.Forms.Page> at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Core\EnumerableExtensions.cs:38,5 
0xEA in Xamarin.Forms.Platform.Android.NavigationRenderer.OnElementChanged at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Renderers\NavigationRenderer.cs:97,4 
0x3 in xfprism.Droid.CustomNavigationRenderer.OnElementChanged at C:\Users\andrej\Desktop\xfprism-kahve\xfprism\xfprism.Droid\Nav_Renderer.cs:24,13 
0xFC in Xamarin.Forms.Platform.Android.VisualElementRenderer<Xamarin.Forms.NavigationPage>.SetElement at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:190,4 
0x2E in Xamarin.Forms.Platform.Android.VisualElementRenderer<Xamarin.Forms.NavigationPage>.Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126,4  
0x21 in Xamarin.Forms.Platform.Android.Platform.CreateRenderer at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:284,4 
0x16 in Xamarin.Forms.Platform.Android.AppCompat.Platform.AddChild at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:248,4  
0x91 in Xamarin.Forms.Platform.Android.AppCompat.Platform.SetPage at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:237,4 
0xA2 in Xamarin.Forms.Platform.Android.FormsAppCompatActivity.InternalSetPage at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\FormsAppCompatActivity.cs:355,4 
0xC in Xamarin.Forms.Platform.Android.FormsAppCompatActivity.SetMainPage at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\FormsAppCompatActivity.cs:429,4  
0x17E in Xamarin.Forms.Platform.Android.FormsAppCompatActivity.LoadApplication at C:\BuildAgent3\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\FormsAppCompatActivity.cs:129,4 
0x2D in xfprism.Droid.MainActivity.OnCreate at C:\Users\andrej\Desktop\xfprism-kahve\xfprism\xfprism.Droid\MainActivity.cs:23,13

來源

2016-05-13 T.Y. Kucuk

你確定錯誤是這樣嗎？我複製你的代碼並編譯。 – Gusman

構建它時不引發異常。你的意思是當你建立它並運行它？ –

啊。你是對的。它建立得很成功。當我調試時遇到異常。 –

如果您還沒有解決方案，嘗試擴展/從Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer而不是Xamarin.Forms.Platform.Android.NavigationRenderer

心靈類的名稱繼承你的渲染，「AppCompat.NavigationPageRenderer」是。

來源

2017-09-22 12:55:28 Subash

Xamarin.Forms-爲什麼CustomRenderer Android for NavigationPage引發InvalidCastException？

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