.NET MAUI 自定义控件属性未附加

问：

我正在使用 .Net Maui，我试图弄清楚如何为组件编写一个简单的验证。例如，我创建了一个名为 ValidatonFor 的包装器，我希望在其中收到要验证的模型字段的名称，但我卡在第一步中。

我的自定义包装器组件未收到为可绑定属性（FieldName 和 ShowValidationError）设置的值。

这是我的组件（这是我演奏的开始）：

public partial class ValidationFor : ContentView
{
    public event EventHandler PropertyChanged;

    public static readonly BindableProperty FieldNameProperty = BindableProperty.Create(nameof(FieldName), typeof(string), typeof(ValidationFor));
    public static readonly BindableProperty ShowValidationErrorProperty = BindableProperty.Create(nameof(ShowValidationError), typeof(bool), typeof(ValidationFor));
    
    public string FieldName
    {
        get => (string)GetValue(FieldNameProperty);
        set => SetValue(FieldNameProperty, value);
    }

    public bool ShowValidationError
    {
        get => (bool)GetValue(ShowValidationErrorProperty);
        set => SetValue(ShowValidationErrorProperty, value);
    }

    private string ErrorMessage = string.Empty;
    private Visibility IsValid = Visibility.Hidden;
    private object chiledElement;

    public ValidationFor()
    {
        InitializeComponent();

        chiledElement = this.GetTemplateChild(this.FieldName);
        
        if(chiledElement is not null)
            (chiledElement as INotifyPropertyChanged).PropertyChanged += ValueChanged;
    }

    public void ValueChanged(object model, PropertyChangedEventArgs args)
    {
        if (args.PropertyName == FieldName.Split('.').Last()) { Validate(chiledElement); }
    }

    private void Validate(object chiledElement)
    {
        dynamic value = chiledElement.GetType().GetProperty(FieldName.Split('.').Last()).GetValue(chiledElement);
        var  results = new List<ValidationResult>();

        ValidationContext context = new ValidationContext(chiledElement) { MemberName = FieldName.Split('.').Last() };
        Validator.TryValidateProperty(value, context, results);

        if (results.Any())
        {
            if (!ShowValidationError)
            {
                this.ErrorMessage = results.First().ErrorMessage;
                this.IsValid = Visibility.Visible;
            }
        }
        else
        {
            this.ErrorMessage = null;
            this.IsValid = Visibility.Hidden;
        }

        PropertyChanged?.Invoke(this, null);
    }
}

在我的测试应用程序中，我是这样使用它的：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:validation="clr-namespace:ValidationLibrary;assembly=ValidationLibrary"
             xmlns:viewModel="clr-namespace:Validation.TestApp"
             x:Class="Validation.TestApp.MainPage"
             x:DataType="viewModel:TestViewModel">

    <VerticalStackLayout VerticalOptions="Start">
        <Frame BorderColor="Black">
            <validation:ValidationFor FieldName="Name" ShowValidationError="False">
                <Entry x:Name="Name" Text="{Binding Name, Mode=TwoWay, UpdateSourceEventName=PropertyChanged}" />
            </validation:ValidationFor>
        </Frame>
    </VerticalStackLayout>
    
</ContentPage>