可重复使用的 xamarin 控件提供 "unable to cast object of type 'Xamarin.forms.xaml.elementnode'..."

Question

我是一个菜鸟类型的编码员，这是我第一次尝试 Xamarin.Forms 中的可重用控件（并且确实是我所有编程中相对最早的控件之一）。在研究中，我发现它说我正在为一个事件分配一个值......我很确定它意味着代码的哪一部分......但我无法弄清楚的是如何使它正确.我正在尝试制作一个 ImageCircle，它下面有一个标签，它是一个可重用的控件。

我的Xaml:

       <?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:controls="clr-namespace:ImageCircle.Forms.Plugin.Abstractions;assembly=ImageCircle.Forms.Plugin"
         x:Class="MyApp.View.Templates.CircleImageButton"
         x:Name="this">
 <ContentView.Content>
    <StackLayout Margin="{StaticResource Margin}" Padding="{StaticResource Padding}" Spacing="0" Grid.Row="{Binding Source={x:Reference this}, Path=GridRow}" Grid.Column="{Binding Source={x:Reference this}, Path=GridColumn}">
        <controls:CircleImage Source="{Binding Source={x:Reference this}, Path=Image}" FillColor="Green" Aspect="AspectFill" Margin="{StaticResource Margin}" >

            <!--error is believed to be caused here-->
<controls:CircleImage.GestureRecognizers>
                <TapGestureRecognizer Tapped="{Binding Source={x:Reference this}, Path=TapGestureCommand}" />
            </controls:CircleImage.GestureRecognizers>

            <controls:CircleImage.WidthRequest>
                <OnPlatform x:TypeArguments="x:Double">
                    <On Platform="Android, iOS">40</On>
                    <On Platform="WinPhone">75</On>
                </OnPlatform>
            </controls:CircleImage.WidthRequest>
            <controls:CircleImage.HeightRequest>
                <OnPlatform x:TypeArguments="x:Double">
                    <On Platform="Android, iOS">40</On>
                    <On Platform="WinPhone">75</On>
                </OnPlatform>
            </controls:CircleImage.HeightRequest>
        </controls:CircleImage>
        <Label Text="{Binding Source={x:Reference this}, Path=LabelCaption}"/>
    </StackLayout>
  </ContentView.Content>
</ContentView>

我背后的代码：

    using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace MyApp.View.Templates
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class CircleImageButton : ContentView
{
    public static readonly BindableProperty ImageProperty = BindableProperty.Create("Image", typeof(string), typeof(CircleImageButton), string.Empty);
    public static readonly BindableProperty GridRowProperty = BindableProperty.Create("GridRow", typeof(int), typeof(CircleImageButton), default(int));
    public static readonly BindableProperty GridColumnProperty = BindableProperty.Create("GridColumn", typeof(int), typeof(CircleImageButton), default(int));
    public static readonly BindableProperty LabelCaptionProperty = BindableProperty.Create("LabelCaption", typeof(string), typeof(CircleImageButton), string.Empty);
    public static readonly BindableProperty TapGestureCommandProperty = BindableProperty.Create("TapGestureCommand", typeof(string), typeof(CircleImageButton), string.Empty);

    public string Image
    {
        get { return (string)GetValue(ImageProperty); }
        set { SetValue(ImageProperty, value); }
    }

    public int GridRow
    {
        get { return (int)GetValue(GridRowProperty); }
        set { SetValue(GridRowProperty, value); }
    }
    public int GridColumn
    {
        get { return (int)GetValue(GridColumnProperty); }
        set { SetValue(GridColumnProperty, value); }
    }
    public string LabelCaption
    {
        get { return (string)GetValue(LabelCaptionProperty); }
        set { SetValue(LabelCaptionProperty, value); }
    }
    public string TapGestureCommand
    {
        get { return (string)GetValue(TapGestureCommandProperty); }
        set { SetValue(TapGestureCommandProperty, value); }
    }

    public CircleImageButton ()
    {
        InitializeComponent ();
    }
}
}

感谢您的帮助，如果您发现更好的方法，请告诉我。我是来学习的。

Answer 1

<controls:CircleImage.GestureRecognizers>
                <TapGestureRecognizer Command="{Binding Source={x:Reference this}, Path=TapGestureCommand}" />
            </controls:CircleImage.GestureRecognizers>

在 XAML 中使用 Command 而非 Tapped 事件进行绑定。

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