容器如何知道孩子何时调用了 InvalidateArrange? [英] How does a container know when a child has called InvalidateArrange?

问题描述

我正在尝试学习在 WinRT XAML 应用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属性，它按预期工作，除了我不知道如何获取子元素的属性回调以触发容器的排列或测量.

I'm trying to learn the basics of creating a custom panel in a WinRT XAML app. I have defined an attached dependency property and it's working as expected except i can't figure out how to get the property's callback for a child element to trigger the arrange or measure of the container.

让孩子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 发布的书中，他们使用 FrameworkPropertyMetadataOptions.AffectsParentArrange 但在 WinRT 中似乎不可用.

What's the proper way to for a child to let it's container know that arrange and measure should be called again? In my WPF 4 unleashed book they use the FrameworkPropertyMetadataOptions.AffectsParentArrange but that doesn't seem to be available in WinRT.

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
}

推荐答案

我参加聚会迟到了，但我朝着相同的方向前进并面临相同的问题.这是我的解决方案.

I'm late to the party, but I went the same direction and faced the same issue. Here is my solution.

在您的回调中，您在将您的属性附加到的子元素上调用 InvalidateArrange:

In your callback you call InvalidateArrange on the child element you attached you property to:

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

但是你真的应该通过改变你的代码来使面板无效:

But you should really invalidate the panel, by changing you code so:

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

它应该可以工作(对我有用).

And it should work (did for me).

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