Vanara/Windows.Forms/Controls/SplitButton.cs

using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;
using static Vanara.PInvoke.ComCtl32;
using static Vanara.PInvoke.User32;

namespace Vanara.Windows.Forms;

/// <summary>The SplitButton is a composite control with which the user can select from a drop-down list bound to the button.</summary>
public class SplitButton : VistaButtonBase
{
	private ContextMenuStrip? contextMenu;
	private bool showingDropdown;
	private ImageList? splitButtonImageList;
	private SplitButtonInfoStyle style = 0;

	/// <summary>Occurs when the split label is clicked.</summary>
	[Description("Occurs when the split button is clicked."), Category("Action")]
	public event EventHandler<SplitMenuEventArgs>? SplitClick;

	/// <summary>Occurs when the split label is clicked, but before the associated context menu is displayed by the control.</summary>
	[Description("Occurs when the split label is clicked, but before the associated context menu is displayed."), Category("Action")]
	public event EventHandler<SplitMenuEventArgs>? SplitMenuOpening;

	/// <summary>Gets or sets the visibility of the split button divider.</summary>
	/// <value><c>true</c> if hiding split separator; otherwise, <c>false</c>.</value>
	[Description("Sets the visibility of the split button divider."), Category("Appearance"), DefaultValue(false)]
	public bool HideSplitSeparator
	{
		get => GetSplitStyle(SplitButtonInfoStyle.BCSS_NOSPLIT);
		set => SetSplitStyle(SplitButtonInfoStyle.BCSS_NOSPLIT, value);
	}

	/// <summary>Gets or sets the alignment of the split button image.</summary>
	/// <value>The split button alignment.</value>
	[Description("Sets the alignment of the split button image."), Category("Appearance"), DefaultValue(typeof(LeftRightAlignment), "Right")]
	public LeftRightAlignment SplitButtonAlignment
	{
		get => GetSplitStyle(SplitButtonInfoStyle.BCSS_ALIGNLEFT) ? LeftRightAlignment.Left : LeftRightAlignment.Right;
		set => SetSplitStyle(SplitButtonInfoStyle.BCSS_ALIGNLEFT, value == LeftRightAlignment.Left);
	}

	/// <summary>Gets or sets the split button image list.</summary>
	/// <value>The split button image list.</value>
	[Description("ImageList containing an image to show on split button."), Category("Appearance"), DefaultValue(null)]
	public ImageList? SplitButtonImageList
	{
		get => splitButtonImageList;
		set
		{
			if (splitButtonImageList != value)
			{
				splitButtonImageList = value;
				if (IsHandleCreated)
				{
					if (splitButtonImageList != null)
						SetSplitInfo(new BUTTON_SPLITINFO(splitButtonImageList.Handle));
					else
						RecreateHandle();
				}
			}
		}
	}

	/// <summary>Gets or sets the associated context menu that is displayed when the split glyph of the button is clicked.</summary>
	[Description("Sets the context menu that is displayed by clicking on the split button."), Category("Behavior"), DefaultValue(null)]
	public ContextMenuStrip? SplitMenuStrip
	{
		get => contextMenu;
		set
		{
			if (value != contextMenu)
			{
				if (contextMenu != null)
					contextMenu.Closed -= contextMenu_Closed;
				contextMenu = value;
				if (contextMenu != null)
					contextMenu.Closed += contextMenu_Closed;
			}
		}
	}

	/// <summary>Gets or sets a value indicating whether to stretch the split button image.</summary>
	/// <value><c>true</c> to stretch split button image; otherwise, <c>false</c>.</value>
	[Description("Stretch glyph, but try to retain aspect ratio."), Category("Appearance"), DefaultValue(false)]
	public bool StretchSplitButtonImage
	{
		get => GetSplitStyle(SplitButtonInfoStyle.BCSS_STRETCH); set => SetSplitStyle(SplitButtonInfoStyle.BCSS_STRETCH, value);
	}

	/// <summary>Gets a <see cref="T:System.Windows.Forms.CreateParams"/> on the base class when creating a window.</summary>
	protected override CreateParams CreateParams
	{
		get
		{
			CreateParams cp = base.CreateParams;
			if (IsPlatformSupported)
				cp.Style |= (int)ButtonStyle.BS_SPLITBUTTON;
			return cp;
		}
	}

	/// <summary>Raises the <see cref="E:System.Windows.Forms.Control.HandleCreated"/> event.</summary>
	/// <param name="e">An <see cref="T:System.EventArgs"/> that contains the event data.</param>
	protected override void OnHandleCreated(EventArgs e)
	{
		base.OnHandleCreated(e);
		if (style != 0)
			SetSplitInfo(new BUTTON_SPLITINFO(style));
		if (splitButtonImageList != null)
			SetSplitInfo(new BUTTON_SPLITINFO(splitButtonImageList.Handle));
	}

	/// <summary>Raises the <see cref="E:SplitClick"/> event.</summary>
	/// <param name="e">The <see cref="SplitMenuEventArgs"/> instance containing the event data.</param>
	protected virtual void OnSplitClick(SplitMenuEventArgs e)
	{
		if (SplitMenuStrip != null)
		{
			if (showingDropdown)
			{
				//SplitMenuStrip.Close();
			}
			else
			{
				SplitMenuOpening?.Invoke(this, e);

				if (!e.PreventOpening)
				{
					SplitMenuStrip.Width = e.DrawArea.Width;
					showingDropdown = true;
					SplitMenuStrip.Show(this, new Point(e.DrawArea.Left, e.DrawArea.Bottom));
				}
			}
		}

		SplitClick?.Invoke(this, e);
	}

	/// <summary>Processes Windows messages.</summary>
	/// <param name="m">The Windows <see cref="T:System.Windows.Forms.Message"/> to process.</param>
	protected override void WndProc(ref Message m)
	{
		if (m.Msg == OCM_NOTIFY)
		{
			NMHDR nmhdr = m.LParam.ToStructure<NMHDR>();
			if ((ButtonNotification)nmhdr.code == ButtonNotification.BCN_DROPDOWN && SplitMenuStrip != null)
				OnSplitClick(new SplitMenuEventArgs(ClientRectangle));
		}
		base.WndProc(ref m);
	}

	private void contextMenu_Closed(object? sender, ToolStripDropDownClosedEventArgs e) => showingDropdown = false;

	private BUTTON_SPLITINFO GetSplitInfo()
	{
		BUTTON_SPLITINFO info = new();
		SendMessage(Handle, ButtonMessage.BCM_GETSPLITINFO, 0, ref info);
		return info;
	}

	private bool GetSplitStyle(SplitButtonInfoStyle btnStyle) => (style & btnStyle) == btnStyle;

	private void SetSplitInfo(BUTTON_SPLITINFO info)
	{
		SendMessage(Handle, ButtonMessage.BCM_SETSPLITINFO, 0, ref info);
		Refresh();
	}

	private void SetSplitStyle(SplitButtonInfoStyle btnStyle, bool value)
	{
		if (value != GetSplitStyle(btnStyle))
		{
			if (value)
				style |= btnStyle;
			else
				style &= ~btnStyle;
			if (IsHandleCreated)
				SetSplitInfo(new BUTTON_SPLITINFO(style));
		}
	}

	/// <summary>Provides data for the clicking of split buttons and the opening of context menus.</summary>
	public class SplitMenuEventArgs : EventArgs
	{
		internal SplitMenuEventArgs(Rectangle drawArea)
		{
			PreventOpening = false;
			DrawArea = drawArea;
		}

		/// <summary>Represents the bounding box of the clicked button.</summary>
		/// <remarks>
		/// A menu should be opened, with top-left coordinates in the left-bottom point of the rectangle and with width equal (or greater)
		/// than the width of the rectangle.
		/// </remarks>
		public Rectangle DrawArea { get; set; }

		/// <summary>Set to true if you want to prevent the menu from opening.</summary>
		public bool PreventOpening { get; set; }
	}
}