support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Controls/Panel/WaterfallPanel.cs

@@ -0,0 +1,85 @@
+using System.Linq;
+using System.Windows;
+using System.Windows.Controls;
+using HandyControl.Data;
+
+namespace HandyControl.Controls
+{
+    public class WaterfallPanel : Panel
+    {
+        public static readonly DependencyProperty GroupsProperty = DependencyProperty.Register(
+            "Groups", typeof(int), typeof(WaterfallPanel), new FrameworkPropertyMetadata(ValueBoxes.Int2Box, FrameworkPropertyMetadataOptions.AffectsMeasure), IsGroupsValid);
+
+        public int Groups
+        {
+            get => (int) GetValue(GroupsProperty);
+            set => SetValue(GroupsProperty, value);
+        }
+
+        private static bool IsGroupsValid(object value)
+        {
+            var v = (int)value;
+            return v >= 1;
+        }
+
+        public static readonly DependencyProperty OrientationProperty = DependencyProperty.Register(
+            "Orientation", typeof(Orientation), typeof(WaterfallPanel), new FrameworkPropertyMetadata(
+                Orientation.Horizontal, FrameworkPropertyMetadataOptions.AffectsMeasure));
+
+        public Orientation Orientation
+        {
+            get => (Orientation) GetValue(OrientationProperty);
+            set => SetValue(OrientationProperty, value);
+        }       
+
+        protected override Size MeasureOverride(Size constraint)
+        {
+            if (Groups < 1) return constraint;
+            var children = InternalChildren;
+            Size panelSize;
+
+            if (Orientation == Orientation.Horizontal)
+            {
+                var heightArr = new double[Groups].ToList();
+                var itemWidth = constraint.Width / Groups;
+                if (double.IsNaN(itemWidth) || double.IsInfinity(itemWidth)) return constraint;
+
+                for (int i = 0, count = children.Count; i < count; i++)
+                {
+                    var child = children[i];
+                    if (child == null) continue;
+
+                    child.Measure(constraint);
+                    var minIndex = heightArr.IndexOf(heightArr.Min());
+                    var minY = heightArr[minIndex];
+                    child.Arrange(new Rect(new Point(minIndex * itemWidth, minY), new Size(itemWidth, child.DesiredSize.Height)));
+
+                    heightArr[minIndex] = minY + child.DesiredSize.Height;
+                }
+                panelSize = new Size(constraint.Width, heightArr.Max());
+            }
+            else
+            {
+                var widthArr = new double[Groups].ToList();
+                var itemHeight = constraint.Height / Groups;
+                if (double.IsNaN(itemHeight) || double.IsInfinity(itemHeight)) return constraint;
+
+                for (int i = 0, count = children.Count; i < count; i++)
+                {
+                    var child = children[i];
+                    if (child == null) continue;
+
+                    child.Measure(constraint);
+                    var minIndex = widthArr.IndexOf(widthArr.Min());
+                    var minX = widthArr[minIndex];
+                    child.Arrange(new Rect(new Point(minX, minIndex * itemHeight), new Size(child.DesiredSize.Width, itemHeight)));
+
+                    widthArr[minIndex] = minX + child.DesiredSize.Width;
+                }
+                panelSize = new Size(widthArr.Max(), constraint.Height);
+            }
+
+            return panelSize;
+        }
+    }
+}