Avalonia/src/Avalonia.Controls/Panel.cs

// Copyright (c) The Avalonia Project. All rights reserved.
// Licensed under the MIT license. See licence.md file in the project root for full license information.

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using Avalonia.Media;
using Avalonia.Metadata;

namespace Avalonia.Controls
{
    /// <summary>
    /// Base class for controls that can contain multiple children.
    /// </summary>
    /// <remarks>
    /// Controls can be added to a <see cref="Panel"/> by adding them to its <see cref="Children"/>
    /// collection. All children are layed out to fill the panel.
    /// </remarks>
    public class Panel : Control, IPanel
    {
        /// <summary>
        /// Defines the <see cref="Background"/> property.
        /// </summary>
        public static readonly StyledProperty<IBrush> BackgroundProperty =
            Border.BackgroundProperty.AddOwner<Panel>();

        private readonly Controls _children = new Controls();

        /// <summary>
        /// Initializes static members of the <see cref="Panel"/> class.
        /// </summary>
        static Panel()
        {
            ClipToBoundsProperty.OverrideDefaultValue<Panel>(true);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Panel"/> class.
        /// </summary>
        public Panel()
        {
            _children.CollectionChanged += ChildrenChanged;
        }

        /// <summary>
        /// Gets or sets the children of the <see cref="Panel"/>.
        /// </summary>
        /// <remarks>
        /// Even though this property can be set, the setter is only intended for use in object
        /// initializers. Assigning to this property does not change the underlying collection,
        /// it simply clears the existing collection and adds the contents of the assigned
        /// collection.
        /// </remarks>
        [Content]
        public Controls Children
        {
            get
            {
                return _children;
            }

            set
            {
                Contract.Requires<ArgumentNullException>(value != null);

                VisualChildren.Clear();
                _children.Clear();
                _children.AddRange(value);
            }
        }

        /// <summary>
        /// Gets or Sets Panel background brush.
        /// </summary>
        public IBrush Background
        {
            get { return GetValue(BackgroundProperty); }
            set { SetValue(BackgroundProperty, value); }
        }

        /// <summary>
        /// Renders the visual to a <see cref="DrawingContext"/>.
        /// </summary>
        /// <param name="context">The drawing context.</param>
        public override void Render(DrawingContext context)
        {
            var background = Background;
            if (background != null)
            {
                var renderSize = Bounds.Size;
                context.FillRectangle(background, new Rect(renderSize));
            }

            base.Render(context);
        }

        /// <summary>
        /// Called when the <see cref="Children"/> collection changes.
        /// </summary>
        /// <param name="sender">The event sender.</param>
        /// <param name="e">The event args.</param>
        protected virtual void ChildrenChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            List<Control> controls;

            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    controls = e.NewItems.OfType<Control>().ToList();
                    LogicalChildren.InsertRange(e.NewStartingIndex, controls);
                    VisualChildren.AddRange(e.NewItems.OfType<Visual>());
                    break;

                case NotifyCollectionChangedAction.Remove:
                    controls = e.OldItems.OfType<Control>().ToList();
                    LogicalChildren.RemoveAll(controls);
                    VisualChildren.RemoveAll(e.OldItems.OfType<Visual>());
                    break;

                case NotifyCollectionChangedAction.Replace:
                    for (var i = 0; i < e.OldItems.Count; ++i)
                    {
                        var index = i + e.OldStartingIndex;
                        var child = (IControl)e.NewItems[i];
                        LogicalChildren[index] = child;
                        VisualChildren[index] = child;
                    }
                    break;

                case NotifyCollectionChangedAction.Reset:
                    controls = e.OldItems.OfType<Control>().ToList();
                    LogicalChildren.Clear();
                    VisualChildren.Clear();
                    VisualChildren.AddRange(_children);
                    break;
            }

            InvalidateMeasure();
        }
    }
}