C# 容器如何知道孩子何时调用了InvalidateArrange？

我正在尝试学习在WinRT XAML应用程序中创建自定义面板的基础知识。我已经定义了一个附加的依赖项属性，它按照预期工作，只是我不知道如何获取子元素的属性回调来触发容器的排列或度量

对于孩子来说，让他们的容器知道应该再次调用“排列”和“测量”的正确方法是什么？在我的WPF 4发行的书中，他们使用了FrameworkPropertyMetadataOptions.AffectsParentArrange，但这在WinRT中似乎不可用

public class SimpleCanvas : Panel
{
    #region Variables
    #region Left Property
    public static double GetLeft(UIElement element)
    {
        if (element == null)
        {
            throw new ArgumentNullException("element");
        }

        object value = element.GetValue(LeftProperty);
        Type valueType = value.GetType();
        return Convert.ToDouble(value);
    } 

    public static void SetLeft(UIElement element, double value)
    {
        if (element == null)
        {
            throw new ArgumentNullException("element");
        }

        element.SetValue(LeftProperty, value);
    }

    public static readonly DependencyProperty LeftProperty =
        DependencyProperty.RegisterAttached("Left", typeof(double), typeof(SimpleCanvas),
        new PropertyMetadata(0, OnLeftPropertyChanged));

    public static void OnLeftPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        UIElement element = (UIElement)source;
        // This doesn't cause ArrangeOverride below to be called
        element.InvalidateArrange();
    }
    #endregion

    #region Top Property
    public static double GetTop(UIElement element)
    {
        if (element == null)
        {
            throw new ArgumentNullException("element");
        }

        object value = element.GetValue(TopProperty);
        return (value == null) ? 0 : (double)value;
    }

    public static void SetTop(UIElement element, double value)
    {
        if (element == null)
        {
            throw new ArgumentNullException("element");
        }

        element.SetValue(TopProperty, value);
    }

    public static readonly DependencyProperty TopProperty =
        DependencyProperty.RegisterAttached("Top", typeof(double), typeof(SimpleCanvas),
        new PropertyMetadata(0, OnTopPropertyChanged));

    public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
    {
        UIElement element = (UIElement)source;
        // This doesn't cause ArrangeOverride below to be called
        element.InvalidateArrange();
    }
    #endregion
    #endregion

    public SimpleCanvas()
    {

    }

    #region Methods
    protected override Size MeasureOverride(Size availableSize)
    {
        foreach (UIElement child in this.Children)
        {
            child.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
        }

        return new Size(0, 0);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        foreach (UIElement child in this.Children)
        {
            double x = 0;
            double y = 0;

            double left = GetLeft(child);
            double top = GetTop(child);

            if (!double.IsNaN(left))
            {
                x = left;
            }
            if (!double.IsNaN(top))
            {
                y = top;
            }

            child.Arrange(new Rect(new Point(x, y), child.DesiredSize));
        }

        return finalSize;
    }
    #endregion
}

---

如果InvalidateArrange单独不起作用，您也可以尝试InvalidateMeasure或UpdateLayout。

我参加聚会迟到了，但我走了同一条路，面临着同样的问题。这是我的解决办法

在回调中，对附加属性的子元素调用InvalidateArrange：

public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
    UIElement element = (UIElement)source;
    // This doesn't cause ArrangeOverride below to be called
    element.InvalidateArrange();
}

但您确实应该通过更改代码使面板无效，以便：

public static void OnTopPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
    UIElement panel= VisualTreeHelper.GetParent(source) as UIElement;
    if(panel != null)       
        panel.InvalidateArrange();
}

---

它应该会起作用（对我来说）

我的子控件有这个问题，它依赖于父控件的

FontSize

。我解决了这个问题，我在父母堆上四处游走，把一切都作废了：

    static MyControl()
    {
        // replace base implementation of the dependent property 
        FontSizeProperty.OverrideMetadata(typeof(Scalar), 
            new FrameworkPropertyMetadata(SystemFonts.MessageFontSize, FrameworkPropertyMetadataOptions.Inherits, OnMeasureInvalidated));
    }

    private static void OnMeasureInvalidated(DependencyObject sender, DependencyPropertyChangedEventArgs args)
    {
        // recurse over parent stack
        while (true)
        {
            var parent = VisualTreeHelper.GetParent(sender) as UIElement;
            if (parent == null) return; // break on root element
            parent.InvalidateMeasure();
            sender = parent;
        }
    }

---

已将回调更改为InvalidateArrange（）、InvalidateMeasure（）和UpdateLayout（），但容器中未命中ArrangeOverride（）和MeasureOverride（）中的断点。可能它会检查是否有任何布局属性更改，如果没有，则不会调用它。您可能需要更改一些布局属性，但这可能会破坏现有的绑定。我不敢相信我花了两天的大部分时间试图解决这个问题。。。谢谢！