// 自定義一個(gè)從左至右排列、從上往下?lián)Q行的面板，并且提供一個(gè)附加屬性可以指示在哪個(gè)子元素前換行
public class MyWrapPanel : Panel
{
    // 定義一個(gè)指示在哪個(gè)子元素前換行的附加屬性
    public static readonly DependencyProperty LineBreakBeforeProperty;

    static MyWrapPanel()
    {
        var metadata = new FrameworkPropertyMetadata
        {
            AffectsMeasure = true,
            AffectsArrange = true
        };

        LineBreakBeforeProperty = DependencyProperty.RegisterAttached("LineBreakBefore",
            typeof(bool), typeof(MyWrapPanel), metadata);
    }

    public static void SetLineBreakBefore(UIElement element, bool value)
    {
        element.SetValue(LineBreakBeforeProperty, value);
    }

    public static bool GetLineBreakBefore(UIElement element)
    {
        return (bool)element.GetValue(LineBreakBeforeProperty);
    }

    protected override Size MeasureOverride(Size availableSize)
    {
        var totalWidth = 0.0;
        var totalHeight = 0.0;
        var rowHeight = 0.0;
        var rowWidth = 0.0;

        foreach (UIElement uiElement in this.Children)
        {
            uiElement.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));

            // 當(dāng)行寬超過(guò)了可用空間的寬度或者子元素設(shè)置了換行的附加屬性時(shí)換行
            if (rowWidth + uiElement.DesiredSize.Width >= availableSize.Width
                || GetLineBreakBefore(uiElement))
            {
                // 面板的總寬度是所有行的最大寬度
                totalWidth = Math.Max(totalWidth, rowWidth);

                // 面板的高度是所有行的高度之和
                totalHeight += rowHeight;

                // 換行后重置行高和行寬
                rowHeight = 0.0;
                rowWidth = 0.0;
            }
            else
            {
                // 每一行的寬度是所有子元素寬度之和
                rowWidth += uiElement.DesiredSize.Width;

                // 每一行的高度都是這一行中所有子元素的最大高度
                rowHeight = Math.Max(rowHeight, uiElement.DesiredSize.Height);
            }
        }

        // 加上最后一行的高度
        totalHeight += rowHeight;

        return new Size(totalWidth, totalHeight);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        var x = 0.0;
        var y = 0.0;
        var rowHeight = 0.0;

        foreach (UIElement uie in this.Children)
        {
            // 如果該子元素將要超出邊界或者設(shè)置了換行，則換一行從頭顯示
            if (x + uie.DesiredSize.Width >= finalSize.Width || GetLineBreakBefore(uie))
            {
                x = 0.0;
                y += rowHeight;

                // 重置行高
                rowHeight = 0.0;
            }

            uie.Arrange(new Rect(x, y, uie.DesiredSize.Width, uie.DesiredSize.Height));

            rowHeight = Math.Max(rowHeight, uie.DesiredSize.Height);
            x = x + uie.DesiredSize.Width;
        }

        return finalSize;
    }
}