WPFXAML系結中的自動欄位更新-簡單示例不起作用

我是 C#、WPF、XAML 和 Binding 的新手，為了學習這個不錯的環境，我自己創建了這個小練習：我想顯示一個包含增值稅和不含增值稅的價格。但是我希望在我更改一個欄位后立即自動更新另一個欄位（所以只要我點擊 Tab）。我已經創建了一個類（感謝幫助我在 Stack Overflow 中發布的另一個問題）來進行數學計算。但是我現在向我們發出問題，因為這些欄位沒有更新。我使用 INotifyPropertyChange 介面，但由于某種原因，它不起作用。這是正在發生的事情：

我使用以下 XAML 代碼：

<Window x:Class="BTWv2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:BTWv2"
        mc:Ignorable="d"
        Title="MainWindow" Height="150" Width="250">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="20" />
            <ColumnDefinition Width="auto" />
            <ColumnDefinition Width="auto" />
            <ColumnDefinition Width="auto" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="20" />

        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="20"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="20"/>

        </Grid.RowDefinitions>

        <Label Grid.Column="1" Grid.Row="1" Content="Amount inc VAT:" VerticalAlignment="Center" HorizontalAlignment="Center"/>
        <TextBox 
                 Grid.Column="2" Grid.Row="1" 
                 VerticalAlignment="Center" HorizontalAlignment="Center" 
                 Width="100" Text="{Binding IncludeVat,Mode=TwoWay}"/>

        <Label Grid.Column="1" Grid.Row="3" Content="Amount excl VAT:" VerticalAlignment="Center" HorizontalAlignment="Center"/>

        <TextBox Text="{Binding ExcludeVat,Mode=TwoWay}"
               Grid.Column="2" Grid.Row="3" 
               VerticalAlignment="Center" HorizontalAlignment="Center" 
               MinWidth="100"
               />
    </Grid>
</Window>

這是實際的 C# 代碼（我使用名為 CalculateVAT 的類來計算數字：

using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
namespace BTWv2
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            CalculateVAT Price = new CalculateVAT();
            Price.IncludeVat = 100;
            DataContext = Price;

        }

        public class CalculateVAT : INotifyPropertyChanged
        {
            private decimal m_IncludeVat; // <- decimal is a better choice for finance

            // To compute VAT we should know the percent; let it be known
            public const decimal Percent = 21.0m;


            public decimal IncludeVat
            {
                get => m_IncludeVat;
                set
                {
                    // negative cash are usually invalid; if it's not the case, drop this check
                    if (value < 0)
                        throw new ArgumentOutOfRangeException(nameof(value));
                    m_IncludeVat = value;
                    Tax = Math.Round(m_IncludeVat / 100 * Percent, 2);
                    NotifyPropertyChanged();
                }
            }

            public decimal ExcludeVat
            {
                get => m_IncludeVat - Tax;
                set
                {
                    if (value < 0)
                        throw new ArgumentOutOfRangeException(nameof(value));
                    m_IncludeVat = Math.Round(value / 100 * (100   Percent), 2);
                    Tax = m_IncludeVat - value;
                    NotifyPropertyChanged();
                }
            }

            // Let's be nice and provide Tax value as well as IncludeVat, ExcludeVat 
            public decimal Tax { get; private set; }

            public override string ToString() =>
              $"Include: {IncludeVat:f2}; exclude: {ExcludeVat:f2} (tax: {Tax:f2})";



            public event PropertyChangedEventHandler? PropertyChanged;

            private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
            {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }

    }
}

Has anyone an idea what I'm missing here? I already tried the UpdateSourceTrigger=PropertyChanged setting in the binding, but that doesn't seem to change anything..

uj5u.com熱心網友回復：

假設您想在從 UI 更改 IncludeVat 時更新 ExcludeVat。您將需要為 IncludeVat 的 setter 中的兩個屬性提升通知屬性。

 public decimal IncludeVat
            {
                get => m_IncludeVat;
                set
                {
                    // negative cash are usually invalid; if it's not the case, drop this check
                    if (value < 0)
                        throw new ArgumentOutOfRangeException(nameof(value));
                    m_IncludeVat = value;
                    Tax = Math.Round(m_IncludeVat / 100 * Percent, 2);
                    NotifyPropertyChanged(nameof(IncludeVat));
                    NotifyPropertyChanged(nameof(ExcludeVat));
                }
            }

這將做的是，當您從 UI 更改 IncludeVat 時，setter 現在會引發為 ExcludeVat 更改的屬性。UI 將嘗試通過呼叫 ExcludeVat 的 getter 進行更新。您獲得 ExcludeVat ：get => m_IncludeVat - Tax; 現在將獲得更新的值，UI 將反映該值。

標籤：c# wpf xaml binding

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