Avalonia/src/Avalonia.Controls/DockPanel.cs

// This source file is adapted from the Windows Presentation Foundation project. 
// (https://github.com/dotnet/wpf/) 
// 
// Licensed to The Avalonia Project under MIT License, courtesy of The .NET Foundation.

using System;

namespace Avalonia.Controls
{
    /// <summary>
    /// Defines the available docking modes for a control in a <see cref="DockPanel"/>.
    /// </summary>
    public enum Dock
    {
        Left = 0,
        Bottom,
        Right,
        Top
    }

    /// <summary>
    /// A panel which arranges its children at the top, bottom, left, right or center.
    /// </summary>
    public class DockPanel : Panel
    {
        /// <summary>
        /// Defines the Dock attached property.
        /// </summary>
        public static readonly AttachedProperty<Dock> DockProperty =
            AvaloniaProperty.RegisterAttached<DockPanel, Control, Dock>("Dock");

        /// <summary>
        /// Defines the <see cref="LastChildFill"/> property.
        /// </summary>
        public static readonly StyledProperty<bool> LastChildFillProperty =
            AvaloniaProperty.Register<DockPanel, bool>(
                nameof(LastChildFill),
                defaultValue: true);

        /// <summary>
        /// Initializes static members of the <see cref="DockPanel"/> class.
        /// </summary>
        static DockPanel()
        {
            AffectsParentMeasure<DockPanel>(DockProperty);
        }

        /// <summary>
        /// Gets the value of the Dock attached property on the specified control.
        /// </summary>
        /// <param name="control">The control.</param>
        /// <returns>The Dock attached property.</returns>
        public static Dock GetDock(Control control)
        {
            return control.GetValue(DockProperty);
        }

        /// <summary>
        /// Sets the value of the Dock attached property on the specified control.
        /// </summary>
        /// <param name="control">The control.</param>
        /// <param name="value">The value of the Dock property.</param>
        public static void SetDock(Control control, Dock value)
        {
            control.SetValue(DockProperty, value);
        }

        /// <summary>
        /// Gets or sets a value which indicates whether the last child of the 
        /// <see cref="DockPanel"/> fills the remaining space in the panel.
        /// </summary>
        public bool LastChildFill
        {
            get { return GetValue(LastChildFillProperty); }
            set { SetValue(LastChildFillProperty, value); }
        }

        /// <summary>
        /// Updates DesiredSize of the DockPanel.  Called by parent Control.  This is the first pass of layout.
        /// </summary>
        /// <remarks>
        /// Children are measured based on their sizing properties and <see cref="Dock" />.  
        /// Each child is allowed to consume all of the space on the side on which it is docked; Left/Right docked
        /// children are granted all vertical space for their entire width, and Top/Bottom docked children are
        /// granted all horizontal space for their entire height.
        /// </remarks>
        /// <param name="constraint">Constraint size is an "upper limit" that the return value should not exceed.</param>
        /// <returns>The Panel's desired size.</returns>
        protected override Size MeasureOverride(Size constraint)
        {
            var children = Children;

            double parentWidth = 0;   // Our current required width due to children thus far.
            double parentHeight = 0;   // Our current required height due to children thus far.
            double accumulatedWidth = 0;   // Total width consumed by children.
            double accumulatedHeight = 0;   // Total height consumed by children.

            for (int i = 0, count = children.Count; i < count; ++i)
            {
                var child = children[i];
                Size childConstraint;             // Contains the suggested input constraint for this child.
                Size childDesiredSize;            // Contains the return size from child measure.

                // Child constraint is the remaining size; this is total size minus size consumed by previous children.
                childConstraint = new Size(Math.Max(0.0, constraint.Width - accumulatedWidth),
                                           Math.Max(0.0, constraint.Height - accumulatedHeight));

                // Measure child.
                child.Measure(childConstraint);
                childDesiredSize = child.DesiredSize;

                // Now, we adjust:
                // 1. Size consumed by children (accumulatedSize).  This will be used when computing subsequent
                //    children to determine how much space is remaining for them.
                // 2. Parent size implied by this child (parentSize) when added to the current children (accumulatedSize).
                //    This is different from the size above in one respect: A Dock.Left child implies a height, but does
                //    not actually consume any height for subsequent children.
                // If we accumulate size in a given dimension, the next child (or the end conditions after the child loop)
                // will deal with computing our minimum size (parentSize) due to that accumulation.
                // Therefore, we only need to compute our minimum size (parentSize) in dimensions that this child does
                //   not accumulate: Width for Top/Bottom, Height for Left/Right.
                switch (GetDock(child))
                {
                    case Dock.Left:
                    case Dock.Right:
                        parentHeight = Math.Max(parentHeight, accumulatedHeight + childDesiredSize.Height);
                        accumulatedWidth += childDesiredSize.Width;
                        break;

                    case Dock.Top:
                    case Dock.Bottom:
                        parentWidth = Math.Max(parentWidth, accumulatedWidth + childDesiredSize.Width);
                        accumulatedHeight += childDesiredSize.Height;
                        break;
                }
            }

            // Make sure the final accumulated size is reflected in parentSize.
            parentWidth = Math.Max(parentWidth, accumulatedWidth);
            parentHeight = Math.Max(parentHeight, accumulatedHeight);

            return (new Size(parentWidth, parentHeight));
        }

        /// <summary>
        /// DockPanel computes a position and final size for each of its children based upon their
        /// <see cref="Dock" /> enum and sizing properties.
        /// </summary>
        /// <param name="arrangeSize">Size that DockPanel will assume to position children.</param>
        protected override Size ArrangeOverride(Size arrangeSize)
        {
            var children = Children;
            int totalChildrenCount = children.Count;
            int nonFillChildrenCount = totalChildrenCount - (LastChildFill ? 1 : 0);

            double accumulatedLeft = 0;
            double accumulatedTop = 0;
            double accumulatedRight = 0;
            double accumulatedBottom = 0;

            for (int i = 0; i < totalChildrenCount; ++i)
            {
                var child = children[i];

                Size childDesiredSize = child.DesiredSize;
                Rect rcChild = new Rect(
                    accumulatedLeft,
                    accumulatedTop,
                    Math.Max(0.0, arrangeSize.Width - (accumulatedLeft + accumulatedRight)),
                    Math.Max(0.0, arrangeSize.Height - (accumulatedTop + accumulatedBottom)));

                if (i < nonFillChildrenCount)
                {
                    switch (GetDock(child))
                    {
                        case Dock.Left:
                            accumulatedLeft += childDesiredSize.Width;
                            rcChild = rcChild.WithWidth(childDesiredSize.Width);
                            break;

                        case Dock.Right:
                            accumulatedRight += childDesiredSize.Width;
                            rcChild = rcChild.WithX(Math.Max(0.0, arrangeSize.Width - accumulatedRight));
                            rcChild = rcChild.WithWidth(childDesiredSize.Width);
                            break;

                        case Dock.Top:
                            accumulatedTop += childDesiredSize.Height;
                            rcChild = rcChild.WithHeight(childDesiredSize.Height);
                            break;

                        case Dock.Bottom:
                            accumulatedBottom += childDesiredSize.Height;
                            rcChild = rcChild.WithY(Math.Max(0.0, arrangeSize.Height - accumulatedBottom));
                            rcChild = rcChild.WithHeight(childDesiredSize.Height);
                            break;
                    }
                }

                child.Arrange(rcChild);
            }

            return (arrangeSize);
        }
    }
}