support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Controls/Base/SimpleItemsControl.cs

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+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.ComponentModel;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Markup;
+
+namespace HandyControl.Controls
+{
+    /// <summary>
+    ///     ItemsControl的轻量级版本
+    /// </summary>
+    [DefaultProperty("Items")]
+    [ContentProperty("Items")]
+    [TemplatePart(Name = ElementPanel, Type = typeof(Panel))]
+    public class SimpleItemsControl : Control
+    {
+        private const string ElementPanel = "PART_Panel";
+
+        public static readonly DependencyProperty ItemTemplateProperty = DependencyProperty.Register(
+            "ItemTemplate", typeof(DataTemplate), typeof(SimpleItemsControl),
+            new FrameworkPropertyMetadata(default(DataTemplate), OnItemTemplateChanged));
+
+        public static readonly DependencyProperty ItemContainerStyleProperty = DependencyProperty.Register(
+            "ItemContainerStyle", typeof(Style), typeof(SimpleItemsControl),
+            new PropertyMetadata(default(Style), OnItemContainerStyleChanged));
+
+        public SimpleItemsControl()
+        {
+            var items = new ObservableCollection<object>();
+            items.CollectionChanged += OnItemsCollectionChanged;
+            Items = items;
+        }
+
+        [Bindable(true)]
+        [Category("Content")]
+        public Style ItemContainerStyle
+        {
+            get => (Style) GetValue(ItemContainerStyleProperty);
+            set => SetValue(ItemContainerStyleProperty, value);
+        }
+
+        [Bindable(true)]
+        public DataTemplate ItemTemplate
+        {
+            get => (DataTemplate) GetValue(ItemTemplateProperty);
+            set => SetValue(ItemTemplateProperty, value);
+        }
+
+        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
+        [Bindable(true)]
+        public Collection<object> Items { get; }
+
+        internal Panel ItemsHost { get; set; }
+
+        public override void OnApplyTemplate()
+        {
+            ItemsHost?.Children.Clear();
+
+            base.OnApplyTemplate();
+
+            ItemsHost = GetTemplateChild(ElementPanel) as Panel;
+            Refresh();
+        }
+
+        private void OnItemsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        {
+            Refresh();
+            UpdateItems();
+        }
+
+        protected virtual DependencyObject GetContainerForItemOverride() => new ContentPresenter();
+
+        protected virtual bool IsItemItsOwnContainerOverride(object item) => item is ContentPresenter;
+
+        protected virtual void PrepareContainerForItemOverride(DependencyObject element, object item)
+        {
+            switch (element)
+            {
+                case ContentControl contentControl:
+                    contentControl.Content = item;
+                    contentControl.ContentTemplate = ItemTemplate;
+                    break;
+                case ContentPresenter contentPresenter:
+                    contentPresenter.Content = item;
+                    contentPresenter.ContentTemplate = ItemTemplate;
+                    break;
+            }
+        }
+
+        private static void OnItemTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            var target = d as SimpleItemsControl;
+            target?.Refresh();
+        }
+
+        private static void OnItemContainerStyleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            var target = d as SimpleItemsControl;
+            target?.Refresh();
+        }
+
+        protected virtual void Refresh()
+        {
+            if (ItemsHost == null) return;
+
+            ItemsHost.Children.Clear();
+            foreach (var item in Items)
+            {
+                DependencyObject container;
+                if (IsItemItsOwnContainerOverride(item))
+                {
+                    container = item as DependencyObject;
+                }
+                else
+                {
+                    container = GetContainerForItemOverride();
+                    PrepareContainerForItemOverride(container, item);
+                }
+
+                if (container is FrameworkElement element)
+                {
+                    element.Style = ItemContainerStyle;
+                    ItemsHost.Children.Add(element);
+                }
+            }
+        }
+
+        protected virtual void UpdateItems()
+        {
+
+        }
+    }
+}