更新：谢谢Andrew KeepCoding的CustomNumberBox类。这真的很有帮助，而且比其他解决方案更容易使用。它不需要数据绑定就能工作。
关于Chris Schaller提出并由Richard Zhang回答的问题，我有一个澄清/用户错误：How to work around UpdateSourceTrigger ignored in NumberBox
我收到以下两个错误：
错误CS1061“NumberBox”不包含“VisualTreeFindName”的定义，并且找不到接受“NumberBox”类型的第一个参数的可访问扩展方法“VisualTreeFindName”（是否缺少using指令或程序集引用？）
错误CS 0103此处的当前上下文中不存在名称ウModel Ж。
下面是对上一个答案的扩展（虽然我的答案是命名空间记帐..）

using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Media;
using System;

namespace Accounting
{
    public static class StaticExtension
    {
        public static FrameworkElement VisualTreeFindName(this DependencyObject element, string name)
        {
            if (element == null || string.IsNullOrWhiteSpace(name))
            {
                return null;
            }
            if (name.Equals((element as FrameworkElement)?.Name, StringComparison.OrdinalIgnoreCase))
            {
                return element as FrameworkElement;
            }
            var childCount = VisualTreeHelper.GetChildrenCount(element);
            for (int i = 0; i < childCount; i++)
            {
                var result = VisualTreeHelper.GetChild(element, i).VisualTreeFindName(name);
                if (result != null)
                {
                    return result;
                }
            }
            return null;
        }
    }
}

下面是主窗口.xaml

<Window
    x:Class="Accounting.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Accounting"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
        <NumberBox
            x:Name="myNumberBox"
            SpinButtonPlacementMode="Compact"
            Loaded="NumberBox_Loaded"
            Value="0" />
    </StackPanel>
</Window>

这里是MainWindow.xaml.cs

using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Media;
using System;
using System.Linq;
using System.Reflection; 

namespace Accounting
{
    public sealed partial class MainWindow : Window
    {
        public MainWindow()
        {
            this.InitializeComponent();
        }

        private void NumberBox_Loaded(object sender, RoutedEventArgs e)
        {
            var box = sender as NumberBox;
            var textBox = box.VisualTreeFindName<TextBox>("InputBox");
            textBox.TextChanged += TextBox_TextChanged;
        }

        private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            string text = (sender as TextBox).Text;
            bool isNumber = !text.Any(t => !char.IsDigit(t));
            if (isNumber)
            {
                double.TryParse(text, out double value);
                if (value != Model.Value)
                    Model.Value = value;
            }
        }
    }
}