c# – 具有绑定模式的WPF UserControl = OneWay

----- MainWindow.xaml -----
<Window x:Class="Test_Binding.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:testBinding="clr-namespace:Test_Binding"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <testBinding:MyLabelledTextBox x:Name="MLTB" LabelText="My custom control: MyLabelledTextBox" Text="{Binding StringData,Mode=OneWay}" />
    </StackPanel>
</Window>

----- MainWindow.xaml.cs -----
using System.Windows;

namespace Test_Binding
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            this.DataContext = new MyDataObject();
            this.InitializeComponent();
        }
    }
}

----- MyDataObject.cs -----
using System.Runtime.CompilerServices; // CallerMemberName
using System.ComponentModel; // INotifyPropertyChanged

namespace Test_Binding
{
    public class MyDataObject : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private string stringData;
        public string StringData
        {
            get { return this.stringData; }
            set
            {
                if (value != this.stringData)
                {
                    this.stringData = value;
                    this.OnPropertyChanged();
                }
            }
        }

        private void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            if (this.PropertyChanged != null)
            {
                this.PropertyChanged(this,new PropertyChangedEventArgs(propertyName));
            }
        }

        public MyDataObject()
        {
            System.Timers.Timer t = new System.Timers.Timer();
            t.Interval = 10000;
            t.Elapsed += t_Elapsed;
            t.Start();
        }

        private void t_Elapsed(object sender,System.Timers.ElapsedEventArgs e)
        {
            this.StringData = ((this.StringData ?? string.Empty).Length >= 4 ? string.Empty : this.StringData + "*");
        }

    }
}

----- MyLabelledTextBox.xaml -----
<UserControl x:Class="Test_Binding.MyLabelledTextBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
  <StackPanel Background="Yellow">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="0.5*" />
            <ColumnDefinition Width="0.5*" />
        </Grid.ColumnDefinitions>   
        <Label x:Name="MLTBLabel" Grid.Row="0" Grid.Column="0" />
        <TextBox x:Name="MLTBTextBox" Grid.Row="0" Grid.Column="1" Background="Yellow" Text="{Binding Text,Mode=TwoWay}" />
    </Grid>
  </StackPanel>
</UserControl>

----- MyLabelledTextBox.xaml.cs -----
using System.Windows;
using System.Windows.Controls;

namespace Test_Binding
{
    /// <summary>
    /// Interaction logic for MyLabelledTextBox.xaml
    /// </summary>
    public partial class MyLabelledTextBox : UserControl
    {
        public static readonly DependencyProperty LabelTextProperty =
            DependencyProperty.Register("LabelText",typeof(string),typeof(MyLabelledTextBox),new PropertyMetadata(string.Empty,MyLabelledTextBox.LabelTextPropertyChanged));
        public string LabelText
        {
            get { return (string)this.GetValue(MyLabelledTextBox.LabelTextProperty); }
            set { this.SetValue(MyLabelledTextBox.LabelTextProperty,value); }
        }

        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register("Text",MyLabelledTextBox.TextPropertyChanged));
        public string Text
        {
            get { return (string)this.GetValue(MyLabelledTextBox.TextProperty); }
            set { this.SetValue(MyLabelledTextBox.TextProperty,value); }
        }

        public MyLabelledTextBox()
        {
            this.InitializeComponent();

            this.MLTBLabel.DataContext = this;
            this.MLTBTextBox.DataContext = this;
            this.MLTBTextBox.TextChanged += new TextChangedEventHandler(this.MLTBTextBox_TextChanged);
        }

        private void MLTBTextBox_TextChanged(object sender,TextChangedEventArgs e)
        {
            this.Text = this.MLTBTextBox.Text; // transfer changes from TextBox to bindable property (bindable property change notification will be fired)
        }

        private static void LabelTextPropertyChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
        {
            ((MyLabelledTextBox)d).MLTBLabel.Content = (string)e.NewValue; // transfer changes from bindable property to Label
        }

        private static void TextPropertyChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
        {
            ((MyLabelledTextBox)d).MLTBTextBox.Text = (string)e.NewValue; // transfer changes from bindable property to TextBox
        }
    }
}

有一个“MyDataObject”类的实例,其属性为“StringData”,使用计时器定期修改.我的用户控件绑定到其属性“StringData”.如果“MainWindow.xaml”文件中的绑定设置为“TwoWay”,则用户控件会不断更新,但如果我使用“OneWay”绑定,则用户控件会更新一次,然后“PropertyChanged” “MyDataObject”类实例的事件不会再次触发,因为它突然没有订阅者.

为什么“OneWay”绑定在被调用一次后停止工作？
什么代码更改将允许“TwoWay”和“OneWay”绑定继续工作？