Xamarin.Forms中的Droid Custom Picker Renderer错误

Question

我已经在Xamarin.Forms应用程序中创建了一个Custom Picker Renderer，在IOS上可以正常运行，但是在运行Android时崩溃。

我已经更新了Visual Studio 2017，并且正在运行Xamarin.Forms 2.3.4.247。

目标Android版本设置为7.1（6.0上出现相同错误）最低Android版本设置为4.3

自定义选择器：

using System;
    using Xamarin.Forms;

    namespace Attest.Combustivel.Infra.Application.Controls
    {
        public class CustomPicker : Picker
        {
            public static readonly BindableProperty FontSizeProperty = BindableProperty.Create(p => p.FontSize, 22);

            public Double FontSize
            {
                get { return (double)GetValue(FontSizeProperty); }
                set
                {
                    if (this.FontSize != value)
                    {
                        SetValue(FontSizeProperty, value);
                    }
                }
            }
        }
    }

自定义Droid Picker渲染器-出现错误：

using Xamarin.Forms;
    using Xamarin.Forms.Platform.Android;

    [assembly: ExportRenderer(typeof(Attest.Combustivel.Infra.Application.Controls.CustomPicker), typeof(Attest.Combustivel.Target.Droid.Renderers.DroidCustomPickerRenderer))]
    namespace Attest.Combustivel.Target.Droid.Renderers
    {
        public class DroidCustomPickerRenderer : PickerRenderer
        {
            protected override void OnElementChanged(ElementChangedEventArgs e)
            {
                base.OnElementChanged(e);

                //if (Control == null)
                //{
                //    return;
                //}

                //var customPicker = e.NewElement as CustomPicker;

                //if (customPicker != null)
                //{
                //    Control.TextSize = Convert.ToSingle(customPicker.FontSize);
                //}
            }
        }
    }

自定义IOS Picker渲染器-工作正常：

using Attest.Combustivel.Infra.Application.Controls;
    using CoreGraphics;
    using System;
    using UIKit;
    using Xamarin.Forms;
    using Xamarin.Forms.Platform.iOS;

    [assembly: ExportRenderer(typeof(Attest.Combustivel.Infra.Application.Controls.CustomPicker), typeof(Attest.Combustivel.Target.Droid.Renderers.IOSCustomPickerRenderer))]
    namespace Attest.Combustivel.Target.Droid.Renderers
    {
        public class IOSCustomPickerRenderer : PickerRenderer
        {
            protected override void OnElementChanged(ElementChangedEventArgs e)
            {
                base.OnElementChanged(e);

                if (Control == null)
                {
                    return;
                }

                var customPicker = e.NewElement as CustomPicker;

                // FontSize
                if (customPicker?.FontSize != null)
                {
                    Control.Font = UIFont.FromName(".SF UI Text", Convert.ToSingle(customPicker.FontSize));
                }
            }
        }
    }

错误：

06-20 16:15:02.261 W/art     ( 7541): JNI RegisterNativeMethods: attempt to register 0 native methods for md5b60ffeb829f638581ab2bb9b1a7f4f3f.TableViewRenderer
06-20 16:15:02.261 W/art     ( 7541): JNI RegisterNativeMethods: attempt to register 0 native methods for md5718175f0eae2ce5b6bb8ba01f33420ae.DroidCustomTableViewRenderer
06-20 16:15:04.911 D/Mono    ( 7541): DllImport attempting to load: '/system/lib/liblog.so'.
06-20 16:15:04.911 D/Mono    ( 7541): DllImport loaded library '/system/lib/liblog.so'.
06-20 16:15:04.911 D/Mono    ( 7541): DllImport searching in: '/system/lib/liblog.so' ('/system/lib/liblog.so').
06-20 16:15:04.911 D/Mono    ( 7541): Searching for '__android_log_print'.
06-20 16:15:04.911 D/Mono    ( 7541): Probing '__android_log_print'.
06-20 16:15:04.911 D/Mono    ( 7541): Found as '__android_log_print'.
06-20 16:15:04.921 I/MonoDroid( 7541): UNHANDLED EXCEPTION:
06-20 16:15:04.981 I/MonoDroid( 7541): System.ArgumentException: element is not of type Xamarin.Forms.TableView
06-20 16:15:04.981 I/MonoDroid( 7541): Parameter name: element
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00008] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:135 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\Platform.cs:289 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:84 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:217 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:68 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:335 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:199 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:137 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\Platform.cs:289 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:84 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:217 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:68 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:335 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:199 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:137 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\Platform.cs:289 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:84 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:217 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:68 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:335 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:199 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:137 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element, Android.Support.V4.App.FragmentManager fragmentManager) [0x00031] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\Platform.cs:325 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Xamarin.Forms.Platform.Android.AppCompat.FragmentContainer.OnCreateView (Android.Views.LayoutInflater inflater, Android.Views.ViewGroup container, Android.OS.Bundle savedInstanceState) [0x00008] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Platform.Android\AppCompat\FragmentContainer.cs:67 
06-20 16:15:04.981 I/MonoDroid( 7541):   at Android.Support.V4.App.Fragment.n_OnCreateView_Landroid_view_LayoutInflater_Landroid_view_ViewGroup_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_inflater, System.IntPtr native_container, System.IntPtr native_savedInstanceState) [0x00022] in <27c17fe440cf491ba8255bcefade6e02>:0 
06-20 16:15:04.981 I/MonoDroid( 7541):   at (wrapper dynamic-method) System.Object:63a8a4b1-f4fe-4a75-89d0-ed93d90f2880 (intptr,intptr,intptr,intptr,intptr)

Answer 1

我们从异常中发现，同一种类型的渲染器更多。

Answer 2

尝试将OnElementChanged的替代方法更改为以下OnElementChanged ：

protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Picker> e)
{
    base.OnElementChanged(e);

    if (Control == null)
    {
        return;
    }

    var customPicker = e.NewElement as CustomPicker;

    if (customPicker != null)
    {
        Control.TextSize = Convert.ToSingle(customPicker.FontSize);
    }
}