c# - 如何使用静态事件将信息从附加行为传递到 View 模型？

Question

在我看来，我有一个文本框的附加属性。附加属性对文本框输入执行验证并执行其他杂务。附加的属性验证例程引发了一个由 View 模型监视的事件。

1. 这是否通过让 View 模型获取无效的文本框来“违反”MVVM 推理？
2. 当包含文本框的用户控件被删除时，GC 将如何处理来自附加属性的静态事件？
3. 如果需要特定代码来避免内存泄漏，那是如何完成的？
4. 有没有更好的方法来做到这一点？

抱歉，列表太长了，但 Google 没有解决这种情况。

感谢任何帮助。感谢您的考虑。

(VS2010.net 4.5)

TIA

View 模型

class CheckInViewModel : SimpleViewModelBase
    {
        public CheckInViewModel()
        {
            InValidTextBoxes = new List<TextBox>();

            Stargate_V.Helpers.ColorMaskingTextBoxBehavior.Validated += (sender, e) =>
                {
                    if (e.valid)
                        InValidTextBoxes.Remove(e.sender);
                    else
                        InValidTextBoxes.Add(e.sender);
                };
        }

        List<TextBox> InValidTextBoxes;


    }

XAML

 <TextBox 
            h:ColorMaskingTextBoxBehavior.Mask="^[MmFf]$"
            Text="{Binding Sex}"
            Height="24" HorizontalAlignment="Right" Margin="0,55,665,0" VerticalAlignment ="Top" Width="36" />

附加属性

  public class ColorMaskingTextBoxBehavior : DependencyObject
    {
        // Entrance point from Xaml 
        public static readonly DependencyProperty MaskProperty = DependencyProperty.RegisterAttached("Mask",
                typeof(string),
                typeof(ColorMaskingTextBoxBehavior),
                new FrameworkPropertyMetadata(OnMaskChanged));
...........................

 // Callback from XAML initialization of the attached property.
    private static void OnMaskChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var textBox = dependencyObject as TextBox;
        var mask = e.NewValue as string;
        textBox.PreviewTextInput -= textBox_PreviewTextInput;
        textBox.PreviewKeyDown -= textBox_PreviewKeyDown;
        DataObject.RemovePastingHandler(textBox, Pasting);
        DataObject.RemoveCopyingHandler(textBox, NoDragCopy);
        CommandManager.RemovePreviewExecutedHandler(textBox, NoCutting);


        if (mask == null)
        {
            textBox.ClearValue(MaskProperty);
            textBox.ClearValue(MaskExpressionProperty);
        }
        else
        {
            textBox.SetValue(MaskProperty, mask);
            SetMaskExpression(textBox, new Regex(mask, RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace));
            textBox.PreviewTextInput += textBox_PreviewTextInput;
            textBox.PreviewKeyDown += textBox_PreviewKeyDown;
            DataObject.AddPastingHandler(textBox, Pasting);
            DataObject.AddCopyingHandler(textBox, NoDragCopy);
            CommandManager.AddPreviewExecutedHandler(textBox, NoCutting);
        }
    }



private static void textBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            var textBox = sender as TextBox;
            var maskExpression = GetMaskExpression(textBox);

            string passHex = (string)textBox.GetValue(PassColorProperty);
            string failHex = (string)textBox.GetValue(FailColorProperty);
            Color passColor = Extensions.ToColorFromHex(passHex);
            Color failColor = Extensions.ToColorFromHex(failHex);

            if (maskExpression == null)
            {
                return;
            }

            var proposedText = GetProposedText(textBox, e.Text);

            if (!maskExpression.IsMatch(proposedText))
            {
                textBox.Background = new SolidColorBrush(failColor);

                ValidationEventArgs args = new ValidationEventArgs();
                args.sender = textBox;
                args.valid = false;
                OnValidation(args);
            }
            else
            {
                textBox.Background = new SolidColorBrush(passColor);

                ValidationEventArgs args = new ValidationEventArgs();
                args.sender = textBox;
                args.valid = true;
                OnValidation(args);
            }
        }

从上面的代码调用的事件

    public static event EventHandler<ValidationEventArgs> Validated;

    static void OnValidation(ValidationEventArgs e)
    {
        EventHandler<ValidationEventArgs> handler = Validated;
        if (handler != null)
        {
            handler(null, e);
        }
    }


public class ValidationEventArgs : EventArgs
{
    public TextBox sender;
    public bool valid;
}

Answer 1

是的，我认为这违反了 MVVM。您的 View 模型应该不知道任何 View 。经常问自己的问题是“我可以在不创建任何 View 的情况下运行我的应用程序吗？”。在这种情况下，您的 View 模型直接与文本框列表交互，因此该模式被打破。

这里有几种方法可以实现您的目标，最简单的可能是在您的 View 模型中创建一个处理程序，当您的 TextBox 文本更改时调用该处理程序:

public delegate void ValidationDelegate(bool isValid);

public class MyViewModel : ViewModelBase
{
    public ValidationDelegate ValidationHandler { get { return (isValid) => OnValidate(isValid); } }

    private void OnValidate(bool isValid)
    {
        // handle the validation event here
    }
}

现在您所需要的只是一个带有附加属性的行为，您可以将其绑定(bind)到此处理程序:

public class ValidateBehavior : Behavior<TextBox>
{
    public ValidationDelegate Validated
    {
        get { return (ValidationDelegate)GetValue(ValidatedProperty); }
        set { SetValue(ValidatedProperty, value); }
    }

    public static readonly DependencyProperty ValidatedProperty =
        DependencyProperty.Register("Validated", typeof(ValidationDelegate), typeof(ValidateBehavior), new PropertyMetadata(null));

    protected override void OnAttached()
    {
        base.OnAttached();
        this.AssociatedObject.TextChanged += ValidateText;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        this.AssociatedObject.TextChanged -= ValidateText;
    }

    private void ValidateText(object sender, TextChangedEventArgs e)
    {
        if (this.Validated != null)
        {
            bool isValid = true; // do text validation here
            this.Validated(isValid);
        }
    }
}

然后最后将行为添加到有问题的 TextBox 并绑定(bind)处理程序:

    <TextBox>
        <i:Interaction.Behaviors>
            <behaviors:ValidateBehavior Validated="{Binding ValidationHandler}"/>
        </i:Interaction.Behaviors>
    </TextBox>

编辑:如果您不想使用混合行为，那么您也可以使用附加行为来完成:

public static class ValidateBehavior
{
    public static ValidationDelegate GetValidate(TextBox textbox)
    {
        return (ValidationDelegate)textbox.GetValue(ValidateProperty);
    }

    public static void SetValidate(TextBox textbox, ValidationDelegate value)
    {
        textbox.SetValue(ValidateProperty, value);
    }

    public static readonly DependencyProperty ValidateProperty =
        DependencyProperty.RegisterAttached(
        "Validate",
        typeof(ValidationDelegate),
        typeof(ValidateBehavior),
        new UIPropertyMetadata(null, OnValidateChanged));

    static void OnValidateChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e)
    {
        var textbox = depObj as TextBox;
        if (textbox == null)
            return;

        if (e.OldValue is ValidationDelegate)
            textbox.TextChanged -= OnTextChanged;

        if (e.NewValue is ValidationDelegate)
            textbox.TextChanged += OnTextChanged;
    }

    static void OnTextChanged(object sender, RoutedEventArgs e)
    {
        if (!Object.ReferenceEquals(sender, e.OriginalSource))
            return;

        var textbox = e.OriginalSource as TextBox;
        if (textbox != null)
        {
            var validate = GetValidate(textbox);
            if (validate != null)
            {
                bool isValid = true; // do text validation here
                validate(isValid);
            }
        }
    }
}

以及相应的 XAML:

<TextBox behaviors:ValidateBehavior.Validate="{Binding ValidationHandler}" />