UniformMinWidthWrapPanel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace KodeFisk.Panels
{
	class UniformMinWidthWrapPanel : Panel
	{
		public UniformMinWidthWrapPanel()
		{
			MinColumnWidth = 200;
		}

		public double MinColumnWidth
		{
			get { return (double)GetValue(MinColumnWidthProperty); }
			set { SetValue(MinColumnWidthProperty, value); }
		}

		// Using a DependencyProperty as the backing store for MinColumnWidth.  This enables animation, styling, binding, etc...
		public static readonly DependencyProperty MinColumnWidthProperty =
			DependencyProperty.Register(nameof(MinColumnWidth), typeof(double), typeof(UniformMinWidthWrapPanel), new PropertyMetadata(null));


		protected override Size MeasureOverride(Size availableSize)
		{
			var finalSize = new Size { Width = availableSize.Width };
			var columns = Math.Floor(finalSize.Width / MinColumnWidth);
			var columnWidth = availableSize.Width / columns;

			var rowHeight = 0d;
			var rowChildCount = 0;
			foreach (var child in Children)
			{
				child.Measure(new Size(columnWidth, availableSize.Height));
				if (rowChildCount < columns)
				{
					rowHeight = Math.Max(child.DesiredSize.Height, rowHeight);
				}
				else
				{
					finalSize.Height += rowHeight;
					rowHeight = child.DesiredSize.Height;
					rowChildCount = 0;
				}
				rowChildCount++;
			}

			finalSize.Height += rowHeight;
			return finalSize;
		}

		protected override Size ArrangeOverride(Size finalSize)
		{
			var columns = Math.Floor(Math.Max(finalSize.Width, MinColumnWidth) / MinColumnWidth);
			var columnWidth = finalSize.Width / columns;
			var posY = 0d;

			var rowHeight = 0d;
			var rowChildCount = 0;
			foreach (var child in Children)
			{
				if (rowChildCount >= columns)
				{
					rowChildCount = 0;
					posY += rowHeight;
					rowHeight = 0;
				}

				child.Arrange(new Rect(columnWidth * rowChildCount, posY, columnWidth, child.DesiredSize.Height));
				rowHeight = Math.Max(child.DesiredSize.Height, rowHeight);
				rowChildCount++;
			}

			return finalSize;
		}
	}
}

great code, but some item overflow. why?

I haven't looked at this code in near a decade, but it looks correct from what I remember. I haven't done XAML in a while either, but my first instinct would be to check whether there is some conflicting constraint on the item; maybe a minsize of some sort that overrides the column width restriction.