WPF 使用附加的属性和行为执行 ICommand

Question

所以我正在学习附加属性和附加行为。我有一个TextBox，每次更改文本时，我想在我的 ViewModel 中执行一些ICommand SomeCommand，我会像这样在视图中绑定：

<TextBox ... TextUpdateCommand="{Binding Path=SomeCommand}" MonitorTextBoxProperty=true />

MonitorTextBoxProperty 只是一个监听TextChanged 事件然后在TextChanged 被触发时执行ICommand SomeCommand 的属性。执行的ICommand SomeCommand 应该来自TextUpdateCommandProperty。如何链接此ICommand SomeCommand 以从OnTextBoxTextChanged 执行它？

代码：

//Property and behaviour for TextChanged event

public static int GetMonitorTextBoxProperty(DependencyObject obj)
{
    return (int)obj.GetValue(MonitorTextBoxProperty);
}

public static void SetMonitorTextBoxProperty(DependencyObject obj, int value)
{
    obj.SetValue(MonitorTextBoxProperty, value);
}

public static readonly DependencyProperty MonitorTextBoxProperty =
     DependencyProperty.RegisterAttached("MonitorTextBox", typeof(bool), typeof(this), new PropertyMetadata(false, OnMonitorTextBoxChanged));

private static void OnMonitorTextBoxChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var textBox = (d as TextBox);
    if (textBox == null) return;

    textBox.TextChanged -= OnTextBoxTextChanged;

    if ((bool)e.NewValue)
    {
        textBox.TextChanged += OnTextBoxTextChanged;
    }
}

private static void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
 {
    // Execute ICommand by command.Execute()
 }

// Property for attaching ICommand that is executed on TextChanged

public static int GetTextUpdateCommandProperty(DependencyObject obj)
{
    return (int)obj.GetValue(TextUpdateCommandProperty);
}

public static void SetTextUpdateCommandProperty(DependencyObject obj, int value)
{
    obj.SetValue(TextUpdateCommandProperty, value);
}

public static readonly DependencyProperty TextUpdateCommandProperty =
    DependencyProperty.RegisterAttached("TextUpdateCommand", typeof(ICommand), typeof(this), new PropertyMetadata(null));

Answer 1

只需使用附加属性的 get 访问器获取 TextBox 的 TextUpdateCommand 属性的当前值。试试这个：

private static void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
{
    var textBox = sender as TextBox;
    var command = GetTextUpdateCommandProperty(textBox);
    if (command != null)
         command.Execute(null);
}

您还应该更改访问器的类型：

public static ICommand GetTextUpdateCommandProperty(DependencyObject obj)
{
    return (ICommand)obj.GetValue(TextUpdateCommandProperty);
}

public static void SetTextUpdateCommandProperty(DependencyObject obj, ICommand value)
{
    obj.SetValue(TextUpdateCommandProperty, value);
}

而typeof(this) 应该在对DependencyProperty.RegisterAttached 的调用中使用typeof(TheClassName)。