pkNX/pkNX.WinForms/Utils/DockPanelSplitter.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace OpenSourceControls;

/// <summary>
/// Code Project article
/// http://www.codeproject.com/KB/WPF/DockPanelSplitter.aspx
///
/// CodePlex project
/// http://wpfcontrols.codeplex.com
///
/// DockPanelSplitter is a splitter control for DockPanels.
/// Add the DockPanelSplitter after the element you want to resize.
/// Set the DockPanel.Dock to define which edge the splitter should work on.
///
/// Follow steps 1a or 1b and then 2 to use this custom control in a XAML file.
///
/// Step 1a) Using this custom control in a XAML file that exists in the current project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is
/// to be used:
///
///     xmlns:OsDps="clr-namespace:DockPanelSplitter"
///
///
/// Step 1b) Using this custom control in a XAML file that exists in a different project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is
/// to be used:
///
///     xmlns:MyNamespace="clr-namespace:DockPanelSplitter;assembly=DockPanelSplitter"
///
/// You will also need to add a project reference from the project where the XAML file lives
/// to this project and Rebuild to avoid compilation errors:
///
///     Right-click on the target project in the Solution Explorer and
///     "Add Reference"->"Projects"->[Select this project]
///
///
/// Step 2)
/// Go ahead and use your control in the XAML file.
///
///     <MyNamespace:DockPanelSplitter/>
///
/// </summary>
public class DockPanelSplitter : Grid
{
    static DockPanelSplitter()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(DockPanelSplitter),
            new FrameworkPropertyMetadata(typeof(DockPanelSplitter)));

        // override the Background property
        BackgroundProperty.OverrideMetadata(typeof(DockPanelSplitter), new FrameworkPropertyMetadata(Brushes.Transparent));

        // override the Dock property to get notifications when Dock is changed
        DockPanel.DockProperty.OverrideMetadata(typeof(DockPanelSplitter),
            new FrameworkPropertyMetadata(Dock.Left, DockChanged));
    }

    /// <summary>
    /// Resize the target element proportionally with the parent container
    /// Set to false if you don't want the element to be resized when the parent is resized.
    /// </summary>
    public bool ProportionalResize
    {
        get => (bool)GetValue(ProportionalResizeProperty);
        set => SetValue(ProportionalResizeProperty, value);
    }

    public static readonly DependencyProperty ProportionalResizeProperty =
        DependencyProperty.Register(nameof(ProportionalResize), typeof(bool), typeof(DockPanelSplitter),
        new UIPropertyMetadata(true));

    /// <summary>
    /// Height or width of splitter, depends on orientation of the splitter
    /// </summary>
    public double Thickness
    {
        get => (double)GetValue(ThicknessProperty);
        set => SetValue(ThicknessProperty, value);
    }

    public static readonly DependencyProperty ThicknessProperty =
        DependencyProperty.Register(nameof(Thickness), typeof(double), typeof(DockPanelSplitter),
        new UIPropertyMetadata(4.0, ThicknessChanged));

    #region Private fields
    private FrameworkElement? element;     // element to resize (target element)
    private double width;                 // current desired width of the element, can be less than minwidth
    private double height;                // current desired height of the element, can be less than minheight
    private double previousParentWidth;   // current width of parent element, used for proportional resize
    private double previousParentHeight;  // current height of parent element, used for proportional resize
    #endregion

    public DockPanelSplitter()
    {
        Loaded += DockPanelSplitterLoaded;
        Unloaded += DockPanelSplitterUnloaded;

        UpdateHeightOrWidth();
    }

    private void DockPanelSplitterLoaded(object sender, RoutedEventArgs e)
    {
        if (Parent is not Panel dp)
            return;

        // Subscribe to the parent's size changed event
        dp.SizeChanged += ParentSizeChanged;

        // Store the current size of the parent DockPanel
        previousParentWidth = dp.ActualWidth;
        previousParentHeight = dp.ActualHeight;

        // Find the target element
        UpdateTargetElement();
    }

    private void DockPanelSplitterUnloaded(object sender, RoutedEventArgs e)
    {
        if (Parent is not Panel dp)
            return;

        // Unsubscribe
        dp.SizeChanged -= ParentSizeChanged;
    }

    private static void DockChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ((DockPanelSplitter)d).UpdateHeightOrWidth();
    }

    private static void ThicknessChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ((DockPanelSplitter)d).UpdateHeightOrWidth();
    }

    private void UpdateHeightOrWidth()
    {
        if (IsHorizontal)
        {
            Height = Thickness;
            Width = double.NaN;
        }
        else
        {
            Width = Thickness;
            Height = double.NaN;
        }
    }

    public bool IsHorizontal
    {
        get
        {
            Dock dock = DockPanel.GetDock(this);
            return dock is Dock.Top or Dock.Bottom;
        }
    }

    /// <summary>
    /// Update the target element (the element the DockPanelSplitter works on)
    /// </summary>
    private void UpdateTargetElement()
    {
        if (Parent is not Panel dp)
            return;

        int i = dp.Children.IndexOf(this);

        // The splitter cannot be the first child of the parent DockPanel
        // The splitter works on the 'older' sibling 
        if (i > 0 && dp.Children.Count > 0)
        {
            element = dp.Children[i - 1] as FrameworkElement ?? throw new InvalidOperationException();
        }
    }

    private void SetTargetWidth(double newWidth)
    {
        ArgumentNullException.ThrowIfNull(element, nameof(element));
        if (newWidth < element.MinWidth)
            newWidth = element.MinWidth;
        if (newWidth > element.MaxWidth)
            newWidth = element.MaxWidth;

        // todo - constrain the width of the element to the available client area
        var dp = (Panel)Parent;
        Dock dock = DockPanel.GetDock(this);
        var t = (MatrixTransform)element.TransformToAncestor(dp);
        if (dock == Dock.Left && newWidth > dp.ActualWidth - t.Matrix.OffsetX - Thickness)
            newWidth = dp.ActualWidth - t.Matrix.OffsetX - Thickness;

        element.Width = newWidth;
    }

    private void SetTargetHeight(double newHeight)
    {
        ArgumentNullException.ThrowIfNull(element, nameof(element));
        if (newHeight < element.MinHeight)
            newHeight = element.MinHeight;
        if (newHeight > element.MaxHeight)
            newHeight = element.MaxHeight;

        // todo - constrain the height of the element to the available client area
        var dp = (Panel)Parent;
        Dock dock = DockPanel.GetDock(this);
        var t = (MatrixTransform)element.TransformToAncestor(dp);
        if (dock == Dock.Top && newHeight > dp.ActualHeight - t.Matrix.OffsetY - Thickness)
            newHeight = dp.ActualHeight - t.Matrix.OffsetY - Thickness;

        element.Height = newHeight;
    }

    private void ParentSizeChanged(object sender, SizeChangedEventArgs e)
    {
        if (!ProportionalResize)
            return;

        if (Parent is not DockPanel dp)
            return;

        ArgumentNullException.ThrowIfNull(element, nameof(element));
        double sx = dp.ActualWidth / previousParentWidth;
        double sy = dp.ActualHeight / previousParentHeight;

        if (!double.IsInfinity(sx))
            SetTargetWidth(element.Width * sx);
        if (!double.IsInfinity(sy))
            SetTargetHeight(element.Height * sy);

        previousParentWidth = dp.ActualWidth;
        previousParentHeight = dp.ActualHeight;
    }

    private double AdjustWidth(double dx, Dock dock)
    {
        if (dock == Dock.Right)
            dx = -dx;

        width += dx;
        SetTargetWidth(width);

        return dx;
    }

    private double AdjustHeight(double dy, Dock dock)
    {
        if (dock == Dock.Bottom)
            dy = -dy;

        height += dy;
        SetTargetHeight(height);

        return dy;
    }

    private Point StartDragPoint;

    protected override void OnMouseEnter(MouseEventArgs e)
    {
        base.OnMouseEnter(e);
        if (!IsEnabled) return;
        Cursor = IsHorizontal ? Cursors.SizeNS : Cursors.SizeWE;
    }

    protected override void OnMouseDown(MouseButtonEventArgs e)
    {
        if (!IsEnabled) return;

        if (!IsMouseCaptured)
        {
            StartDragPoint = e.GetPosition(Parent as IInputElement);
            UpdateTargetElement();
            if (element != null)
            {
                width = element.ActualWidth;
                height = element.ActualHeight;
                CaptureMouse();
            }
        }

        base.OnMouseDown(e);
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        if (IsMouseCaptured)
        {
            Point ptCurrent = e.GetPosition(Parent as IInputElement);
            Point delta = new(ptCurrent.X - StartDragPoint.X, ptCurrent.Y - StartDragPoint.Y);
            Dock dock = DockPanel.GetDock(this);

            if (IsHorizontal)
                delta.Y = AdjustHeight(delta.Y, dock);
            else
                delta.X = AdjustWidth(delta.X, dock);

            bool isBottomOrRight = dock is Dock.Right or Dock.Bottom;

            // When docked to the bottom or right, the position has changed after adjusting the size
            if (isBottomOrRight)
                StartDragPoint = e.GetPosition(Parent as IInputElement);
            else
                StartDragPoint.Offset(delta.X, delta.Y);
        }
        base.OnMouseMove(e);
    }

    protected override void OnMouseUp(MouseButtonEventArgs e)
    {
        if (IsMouseCaptured)
        {
            ReleaseMouseCapture();
        }
        base.OnMouseUp(e);
    }
}