Avalonia/src/Avalonia.Controls/Grid.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.Diagnostics;
using System.Linq;
using System.Reactive.Linq;
using System.Runtime.CompilerServices;
using Avalonia.Collections;
using Avalonia.Controls.Utils;
using Avalonia.VisualTree;
using JetBrains.Annotations;

namespace Avalonia.Controls
{
    /// <summary>
    /// Lays out child controls according to a grid.
    /// </summary>
    public class Grid : Panel
    {
        /// <summary>
        /// Defines the Column attached property.
        /// </summary>
        public static readonly AttachedProperty<int> ColumnProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, int>(
                "Column",
                validate: ValidateColumn);

        /// <summary>
        /// Defines the ColumnSpan attached property.
        /// </summary>
        public static readonly AttachedProperty<int> ColumnSpanProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, int>("ColumnSpan", 1);

        /// <summary>
        /// Defines the Row attached property.
        /// </summary>
        public static readonly AttachedProperty<int> RowProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, int>(
                "Row",
                validate: ValidateRow);

        /// <summary>
        /// Defines the RowSpan attached property.
        /// </summary>
        public static readonly AttachedProperty<int> RowSpanProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, int>("RowSpan", 1);

        public static readonly AttachedProperty<bool> IsSharedSizeScopeProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, bool>("IsSharedSizeScope", false);

        protected override void OnMeasureInvalidated()
        {
            base.OnMeasureInvalidated();
            _sharedSizeHost?.InvalidateMeasure(this);
        }

        private SharedSizeScopeHost _sharedSizeHost;

        /// <summary>
        /// Defines the SharedSizeScopeHost private property. 
        /// The ampersands are used to make accessing the property via xaml inconvenient.
        /// </summary>
        internal static readonly AttachedProperty<SharedSizeScopeHost> s_sharedSizeScopeHostProperty =
            AvaloniaProperty.RegisterAttached<Grid, Control, SharedSizeScopeHost>("&&SharedSizeScopeHost");

        private ColumnDefinitions _columnDefinitions;

        private RowDefinitions _rowDefinitions;

        static Grid()
        {
            AffectsParentMeasure<Grid>(ColumnProperty, ColumnSpanProperty, RowProperty, RowSpanProperty);
            IsSharedSizeScopeProperty.Changed.AddClassHandler<Control>(IsSharedSizeScopeChanged);
        }

        public Grid()
        {
            this.AttachedToVisualTree += Grid_AttachedToVisualTree;
            this.DetachedFromVisualTree += Grid_DetachedFromVisualTree;
        }

        /// <summary>
        /// Gets or sets the columns definitions for the grid.
        /// </summary>
        public ColumnDefinitions ColumnDefinitions
        {
            get
            {
                if (_columnDefinitions == null)
                {
                    ColumnDefinitions = new ColumnDefinitions();
                }

                return _columnDefinitions;
            }

            set
            {
                if (_columnDefinitions != null)
                {
                    throw new NotSupportedException("Reassigning ColumnDefinitions not yet implemented.");
                }

                _columnDefinitions = value;
                _columnDefinitions.TrackItemPropertyChanged(_ => InvalidateMeasure());
                _columnDefinitions.CollectionChanged += (_, __) => InvalidateMeasure();
            }
        }

        /// <summary>
        /// Gets or sets the row definitions for the grid.
        /// </summary>
        public RowDefinitions RowDefinitions
        {
            get
            {
                if (_rowDefinitions == null)
                {
                    RowDefinitions = new RowDefinitions();
                }

                return _rowDefinitions;
            }

            set
            {
                if (_rowDefinitions != null)
                {
                    throw new NotSupportedException("Reassigning RowDefinitions not yet implemented.");
                }

                _rowDefinitions = value;
                _rowDefinitions.TrackItemPropertyChanged(_ => InvalidateMeasure());
                _rowDefinitions.CollectionChanged += (_, __) => InvalidateMeasure();
            }
        }

        /// <summary>
        /// Gets the value of the Column attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <returns>The control's column.</returns>
        public static int GetColumn(AvaloniaObject element)
        {
            return element.GetValue(ColumnProperty);
        }

        /// <summary>
        /// Gets the value of the ColumnSpan attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <returns>The control's column span.</returns>
        public static int GetColumnSpan(AvaloniaObject element)
        {
            return element.GetValue(ColumnSpanProperty);
        }

        /// <summary>
        /// Gets the value of the Row attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <returns>The control's row.</returns>
        public static int GetRow(AvaloniaObject element)
        {
            return element.GetValue(RowProperty);
        }

        /// <summary>
        /// Gets the value of the RowSpan attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <returns>The control's row span.</returns>
        public static int GetRowSpan(AvaloniaObject element)
        {
            return element.GetValue(RowSpanProperty);
        }

        /// <summary>
        /// Sets the value of the Column attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <param name="value">The column value.</param>
        public static void SetColumn(AvaloniaObject element, int value)
        {
            element.SetValue(ColumnProperty, value);
        }

        /// <summary>
        /// Sets the value of the ColumnSpan attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <param name="value">The column span value.</param>
        public static void SetColumnSpan(AvaloniaObject element, int value)
        {
            element.SetValue(ColumnSpanProperty, value);
        }

        /// <summary>
        /// Sets the value of the Row attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <param name="value">The row value.</param>
        public static void SetRow(AvaloniaObject element, int value)
        {
            element.SetValue(RowProperty, value);
        }

        /// <summary>
        /// Sets the value of the RowSpan attached property for a control.
        /// </summary>
        /// <param name="element">The control.</param>
        /// <param name="value">The row span value.</param>
        public static void SetRowSpan(AvaloniaObject element, int value)
        {
            element.SetValue(RowSpanProperty, value);
        }

        /// <summary>
        /// Gets the result of the last column measurement.
        /// Use this result to reduce the arrange calculation.
        /// </summary>
        private GridLayout.MeasureResult _columnMeasureCache;

        /// <summary>
        /// Gets the result of the last row measurement.
        /// Use this result to reduce the arrange calculation.
        /// </summary>
        private GridLayout.MeasureResult _rowMeasureCache;

        /// <summary>
        /// Gets the row layout as of the last measure.
        /// </summary>
        private GridLayout _rowLayoutCache;

        /// <summary>
        /// Gets the column layout as of the last measure.
        /// </summary>
        private GridLayout _columnLayoutCache;

        /// <summary>
        /// Measures the grid.
        /// </summary>
        /// <param name="constraint">The available size.</param>
        /// <returns>The desired size of the control.</returns>
        protected override Size MeasureOverride(Size constraint)
        {
            // Situation 1/2:
            // If the grid doesn't have any column/row definitions, it behaves like a normal panel.
            // GridLayout supports this situation but we handle this separately for performance.

            if (ColumnDefinitions.Count == 0 && RowDefinitions.Count == 0)
            {
                var maxWidth = 0.0;
                var maxHeight = 0.0;
                foreach (var child in Children.OfType<Control>())
                {
                    child.Measure(constraint);
                    maxWidth = Math.Max(maxWidth, child.DesiredSize.Width);
                    maxHeight = Math.Max(maxHeight, child.DesiredSize.Height);
                }

                maxWidth = Math.Min(maxWidth, constraint.Width);
                maxHeight = Math.Min(maxHeight, constraint.Height);
                return new Size(maxWidth, maxHeight);
            }

            // Situation 2/2:
            // If the grid defines some columns or rows.
            // Debug Tip:
            //     - GridLayout doesn't hold any state, so you can drag the debugger execution
            //       arrow back to any statements and re-run them without any side-effect.

            var measureCache = new Dictionary<Control, Size>();
            var (safeColumns, safeRows) = GetSafeColumnRows();
            var columnLayout = new GridLayout(ColumnDefinitions);
            var rowLayout = new GridLayout(RowDefinitions);
            // Note: If a child stays in a * or Auto column/row, use constraint to measure it.
            columnLayout.AppendMeasureConventions(safeColumns, child => MeasureOnce(child, constraint).Width);
            rowLayout.AppendMeasureConventions(safeRows, child => MeasureOnce(child, constraint).Height);

            // Calculate measurement.
            var columnResult = columnLayout.Measure(constraint.Width);
            var rowResult = rowLayout.Measure(constraint.Height);

            // Use the results of the measurement to measure the rest of the children.
            foreach (var child in Children.OfType<Control>())
            {
                var (column, columnSpan) = safeColumns[child];
                var (row, rowSpan) = safeRows[child];
                var width = Enumerable.Range(column, columnSpan).Select(x => columnResult.LengthList[x]).Sum();
                var height = Enumerable.Range(row, rowSpan).Select(x => rowResult.LengthList[x]).Sum();

                MeasureOnce(child, new Size(width, height));
            }

            // Cache the measure result and return the desired size.
            _columnMeasureCache = columnResult;
            _rowMeasureCache = rowResult;
            _rowLayoutCache = rowLayout;
            _columnLayoutCache = columnLayout;

            if (_sharedSizeHost?.ParticipatesInScope(this) ?? false)
            {
                _sharedSizeHost.UpdateMeasureStatus(this, rowResult, columnResult);
            }

            return new Size(columnResult.DesiredLength, rowResult.DesiredLength);

            // Measure each child only once.
            // If a child has been measured, it will just return the desired size.
            Size MeasureOnce(Control child, Size size)
            {
                if (measureCache.TryGetValue(child, out var desiredSize))
                {
                    return desiredSize;
                }

                child.Measure(size);
                desiredSize = child.DesiredSize;
                measureCache[child] = desiredSize;
                return desiredSize;
            }
        }

        /// <summary>
        /// Arranges the grid's children.
        /// </summary>
        /// <param name="finalSize">The size allocated to the control.</param>
        /// <returns>The space taken.</returns>
        protected override Size ArrangeOverride(Size finalSize)
        {
            // Situation 1/2:
            // If the grid doesn't have any column/row definitions, it behaves like a normal panel.
            // GridLayout supports this situation but we handle this separately for performance.

            if (ColumnDefinitions.Count == 0 && RowDefinitions.Count == 0)
            {
                foreach (var child in Children.OfType<Control>())
                {
                    child.Arrange(new Rect(finalSize));
                }

                return finalSize;
            }

            // Situation 2/2:
            // If the grid defines some columns or rows.
            // Debug Tip:
            //     - GridLayout doesn't hold any state, so you can drag the debugger execution
            //       arrow back to any statements and re-run them without any side-effect.

            var (safeColumns, safeRows) = GetSafeColumnRows();
            var columnLayout = _columnLayoutCache;
            var rowLayout = _rowLayoutCache;

            var rowCache = _rowMeasureCache;
            var columnCache = _columnMeasureCache;

            if (_sharedSizeHost?.ParticipatesInScope(this) ?? false)
            {
                (rowCache, columnCache) = _sharedSizeHost.HandleArrange(this, _rowMeasureCache, _columnMeasureCache);
            
                rowCache = rowLayout.Measure(finalSize.Height, rowCache.LeanLengthList);
                columnCache = columnLayout.Measure(finalSize.Width, columnCache.LeanLengthList);
            }

            // Calculate for arrange result.
            var columnResult = columnLayout.Arrange(finalSize.Width, columnCache);
            var rowResult = rowLayout.Arrange(finalSize.Height, rowCache);
            // Arrange the children.
            foreach (var child in Children.OfType<Control>())
            {
                var (column, columnSpan) = safeColumns[child];
                var (row, rowSpan) = safeRows[child];
                var x = Enumerable.Range(0, column).Sum(c => columnResult.LengthList[c]);
                var y = Enumerable.Range(0, row).Sum(r => rowResult.LengthList[r]);
                var width = Enumerable.Range(column, columnSpan).Sum(c => columnResult.LengthList[c]);
                var height = Enumerable.Range(row, rowSpan).Sum(r => rowResult.LengthList[r]);
                child.Arrange(new Rect(x, y, width, height));
            }

            // Assign the actual width.
            for (var i = 0; i < ColumnDefinitions.Count; i++)
            {
                ColumnDefinitions[i].ActualWidth = columnResult.LengthList[i];
            }

            // Assign the actual height.
            for (var i = 0; i < RowDefinitions.Count; i++)
            {
                RowDefinitions[i].ActualHeight = rowResult.LengthList[i];
            }

            // Return the render size.
            return finalSize;
        }

        /// <summary>
        /// Tests whether this grid belongs to a shared size scope.
        /// </summary>
        /// <returns>True if the grid is registered in a shared size scope.</returns>
        internal bool HasSharedSizeScope()
        {
            return _sharedSizeHost != null;
        }

        /// <summary>
        /// Called when the SharedSizeScope for a given grid has changed.
        /// Unregisters the grid from it's current scope and finds a new one (if any) 
        /// </summary>
        /// <remarks>
        /// This method, while not efficient, correctly handles nested scopes, with any order of scope changes.
        /// </remarks>
        internal void SharedScopeChanged()
        {
            _sharedSizeHost?.UnegisterGrid(this);

            _sharedSizeHost = null;
            var scope = this.GetVisualAncestors().OfType<Control>()
                .FirstOrDefault(c => c.GetValue(IsSharedSizeScopeProperty));

            if (scope != null)
            {
                _sharedSizeHost = scope.GetValue(s_sharedSizeScopeHostProperty);
                _sharedSizeHost.RegisterGrid(this);
            }

            InvalidateMeasure();
        }

        /// <summary>
        /// Callback when a grid is attached to the visual tree. Finds the innermost SharedSizeScope and registers the grid 
        /// in it.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="e">The event arguments.</param>
        private void Grid_AttachedToVisualTree(object sender, VisualTreeAttachmentEventArgs e)
        {
            var scope =
                new Control[] { this }.Concat(this.GetVisualAncestors().OfType<Control>())
                    .FirstOrDefault(c => c.GetValue(IsSharedSizeScopeProperty));

            if (_sharedSizeHost != null)
                throw new AvaloniaInternalException("Shared size scope already present when attaching to visual tree!");

            if (scope != null)
            {
                _sharedSizeHost = scope.GetValue(s_sharedSizeScopeHostProperty);
                _sharedSizeHost.RegisterGrid(this);
            }
        }

        /// <summary>
        /// Callback when a grid is detached from the visual tree. Unregisters the grid from its SharedSizeScope if any.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="e">The event arguments.</param>
        private void Grid_DetachedFromVisualTree(object sender, VisualTreeAttachmentEventArgs e)
        {
            _sharedSizeHost?.UnegisterGrid(this);
            _sharedSizeHost = null;
        }


        /// <summary>
        /// Get the safe column/columnspan and safe row/rowspan.
        /// This method ensures that none of the children has a column/row outside the bounds of the definitions.
        /// </summary>
        [Pure]
        private (Dictionary<Control, (int index, int span)> safeColumns,
            Dictionary<Control, (int index, int span)> safeRows) GetSafeColumnRows()
        {
            var columnCount = ColumnDefinitions.Count;
            var rowCount = RowDefinitions.Count;
            columnCount = columnCount == 0 ? 1 : columnCount;
            rowCount = rowCount == 0 ? 1 : rowCount;
            var safeColumns = Children.OfType<Control>().ToDictionary(child => child,
                child => GetSafeSpan(columnCount, GetColumn(child), GetColumnSpan(child)));
            var safeRows = Children.OfType<Control>().ToDictionary(child => child,
                child => GetSafeSpan(rowCount, GetRow(child), GetRowSpan(child)));
            return (safeColumns, safeRows);
        }

        /// <summary>
        /// Gets the safe row/column and rowspan/columnspan for a specified range.
        /// The user may assign row/column properties outside the bounds of the row/column count, this method coerces them inside.
        /// </summary>
        /// <param name="length">The row or column count.</param>
        /// <param name="userIndex">The row or column that the user assigned.</param>
        /// <param name="userSpan">The rowspan or columnspan that the user assigned.</param>
        /// <returns>The safe row/column and rowspan/columnspan.</returns>
        [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static (int index, int span) GetSafeSpan(int length, int userIndex, int userSpan)
        {
            var index = userIndex;
            var span = userSpan;

            if (index < 0)
            {
                span = index + span;
                index = 0;
            }

            if (span <= 0)
            {
                span = 1;
            }

            if (userIndex >= length)
            {
                index = length - 1;
                span = 1;
            }
            else if (userIndex + userSpan > length)
            {
                span = length - userIndex;
            }

            return (index, span);
        }

        private static int ValidateColumn(AvaloniaObject o, int value)
        {
            if (value < 0)
            {
                throw new ArgumentException("Invalid Grid.Column value.");
            }

            return value;
        }

        private static int ValidateRow(AvaloniaObject o, int value)
        {
            if (value < 0)
            {
                throw new ArgumentException("Invalid Grid.Row value.");
            }

            return value;
        }

        /// <summary>
        /// Called when the value of <see cref="Grid.IsSharedSizeScopeProperty"/> changes for a control.
        /// </summary>
        /// <param name="source">The control that triggered the change.</param>
        /// <param name="arg2">Change arguments.</param>
        private static void IsSharedSizeScopeChanged(Control source, AvaloniaPropertyChangedEventArgs arg2)
        {
            var shouldDispose = (arg2.OldValue is bool d) && d;
            if (shouldDispose)
            {
                var host = source.GetValue(s_sharedSizeScopeHostProperty) as SharedSizeScopeHost;
                if (host == null)
                    throw new AvaloniaInternalException("SharedScopeHost wasn't set when IsSharedSizeScope was true!");
                host.Dispose();
                source.ClearValue(s_sharedSizeScopeHostProperty);
            }

            var shouldAssign = (arg2.NewValue is bool a) && a;
            if (shouldAssign)
            {
                if (source.GetValue(s_sharedSizeScopeHostProperty) != null)
                    throw new AvaloniaInternalException("SharedScopeHost was already set when IsSharedSizeScope is only now being set to true!");
                source.SetValue(s_sharedSizeScopeHostProperty, new SharedSizeScopeHost());
            }

            // if the scope has changed, notify the descendant grids that they need to update.
            if (source.GetVisualRoot() != null && shouldAssign || shouldDispose)
            {
                var participatingGrids = new[] { source }.Concat(source.GetVisualDescendants()).OfType<Grid>();

                foreach (var grid in participatingGrids)
                    grid.SharedScopeChanged();

            }
        }
    }
}