xamarin 渲染器无效转换

Question

为了能够创建需要在 Xamarin 环境中本地完成的样式，我使用了自定义渲染器。在 android 方面，我收到了一个 System.InvalidCastException，我不知道如何解决这个问题。由于 this guys 对我收到的先前错误的建议（没有默认构造函数接受 0 个参数错误），我目前正在包装一个 Android.Widget.StackView。该错误似乎不是由于声明或实例化而发生的，而是当我将其添加到 ContentView 并发生在 return 时（通过注释掉该行发现，如下所示）。

        MainPage = new ContentPage {
            Content = new StackLayout {
                VerticalOptions = LayoutOptions.Center,
                Children = {
                    item1,
                    item2,
                    item3,
                    item4,
                    item5,
                    item6,
                    //rendererIWantToAdd,//taking out this line make it work. adding it breaks it
                }
            }
        };

代码

渲染视图

public class RendererView :  View
{

    public static readonly BindableProperty ImageProperty = BindableProperty.Create(
        propertyName: "Src",
        returnType: typeof(string),
        declaringType: typeof(string),
        defaultValue: ""
    );
    public String Src
    {
        get { return (string)GetValue(ImageProperty); }
        set { SetValue(ImageProperty, value); }
    }

    public static readonly BindableProperty TextProperty = BindableProperty.Create(
        propertyName: "Text",
        returnType: typeof(string),
        declaringType: typeof(string),
        defaultValue: "Hello World"
    );
    public String Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }

    public static readonly BindableProperty ColorProperty = BindableProperty.Create(
        propertyName: "Color",
        returnType: typeof(string),
        declaringType: typeof(string),
        defaultValue: "#AAAAAA"
    );
    public String Color
    {
        get { return (string) GetValue(ColorProperty); }
        set { SetValue(ColorProperty, value); }
    }
}

RendererViewAndroid

[assembly: ExportRenderer(typeof(Project.RendererView), typeof(stackViewWrapper))]
namespace Project.Droid
{
    public class RendererViewAndroid : ViewRenderer<RendererView, stackViewWrapper>
    {

        Android.Widget.TextView label;
        Android.Widget.ImageView image;

        protected override void OnElementChanged(ElementChangedEventArgs<RendererView> e)
        {
            base.OnElementChanged(e);
            if (Control == null)
            {
                createItem(e);
            }

            if (e.OldElement != null)
            {

                unsubscribe(e);
            }

            if (e.NewElement != null)
            {
                subscribe(e);
            }



        }


        protected void createItem(ElementChangedEventArgs<RendererView> e)
        {


            SetNativeControl(new stackViewWrapper());
            label = new Android.Widget.TextView(Context)
            {
                Text = Element.Text
            };

            image = new Android.Widget.ImageView(Context);
            if (!string.IsNullOrWhiteSpace(Element.Src))
            {
                Context.Resources.GetBitmapAsync(Element.Src).ContinueWith((t) =>
                {
                    var bitmap = t.Result;
                    if (bitmap != null)
                    {
                        image.SetImageBitmap(bitmap);
                        bitmap.Dispose();
                    }
                }, TaskScheduler.FromCurrentSynchronizationContext());

            }
            else {
            //  // clear the image
                image.SetImageBitmap(null);
            }


            Control.AddView(image);
            Control.AddView(label);



        }
        protected void subscribe(ElementChangedEventArgs<RendererView> e)
        {

        }
        protected void unsubscribe(ElementChangedEventArgs<RendererView> e)
        {

        }





        protected override void Dispose(bool disposing)
        {
            base.Dispose(disposing);
        }





    }


    public  class stackViewWrapper : Android.Views.View
    {
        public stackViewWrapper() : base(Android.App.Application.Context)
        {
        }
    }
}

错误堆栈跟踪

System.InvalidCastException: Specified cast is not valid. at at (wrapper castclass) System.Object:__castclass_with_cache (object,intptr,intptr) at Xamarin.Forms.Registrar1[TRegistrable].GetHandler (System.Type type) [0x0001b] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Registrar.cs:24 at Xamarin.Forms.Registrar1[TRegistrable].GetHandler[TOut] (System.Type type) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Registrar.cs:29 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x00006] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:281 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:72 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:204 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:56 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:327 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (Xamarin.Forms.Platform.Android.TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:195 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:128 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:282 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:72 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:204 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:56 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:327 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (Xamarin.Forms.Platform.Android.TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:195 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:128 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:282 at Xamarin.Forms.Platform.Android.Platform.AddChild (Xamarin.Forms.VisualElement view, Boolean layout) [0x00015] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:518 at Xamarin.Forms.Platform.Android.Platform.SetPage (Xamarin.Forms.Page newRoot) [0x00089] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:406 at Xamarin.Forms.Platform.Android.FormsApplicationActivity.InternalSetPage (Xamarin.Forms.Page page) [0x000b7] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\FormsApplicationActivity.cs:286 at Xamarin.Forms.Platform.Android.FormsApplicationActivity.SetMainPage () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\FormsApplicationActivity.cs:305 at Xamarin.Forms.Platform.Android.FormsApplicationActivity.LoadApplication (Xamarin.Forms.Application application) [0x0002d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\FormsApplicationActivity.cs:108 at Project.Droid.MainActivity.OnCreate (Android.OS.Bundle bundle) [0x000ae] in /Users/ryan/project-app-xamarin/Project/Project.Droid/MainActivity.cs:47 at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (IntPtr jnienv, IntPtr native__this, IntPtr native_savedInstanceState) [0x00011] in /Users/builder/data/lanes/3340/4e275588/source/monodroid/src/Mono.Android/platforms/android-23/src/generated/Android.App.Activity.cs:2426 at at (wrapper dynamic-method) System.Object:688deba4-7150-4f17-9062-10e53a94164c (intptr,intptr,intptr)

Answer 1

不确定这是否真的是您问题的根源，但如果不是，肯定会给您带来麻烦。

在您的 RendererView 中，您的所有绑定属性都应将其 declaringType 设置为它们在其中声明的 class，即 RendererView。

例如，您的第一个绑定属性应该如下所示：

public static readonly BindableProperty ImageProperty = BindableProperty.Create(
    propertyName: "Src",
    returnType: typeof(string),
    declaringType: typeof(RendererView),
    defaultValue: ""
);

然后对所有其他人做同样的事情。如果那不能解决问题，一定要告诉我。

编辑：根据下面 OP 的评论，初始错误来自 ExportRenderer 行，需要声明 RendererView 而不是 stackViewWrapper ，如下所示：

[assembly: ExportRenderer(typeof(Project.RendererView), typeof(RendererViewAndroid))]

xamarin 渲染器无效转换

xamarin renderer invalid cast

custom-renderer

xamarin

代码

渲染视图

RendererViewAndroid

错误堆栈跟踪