Vanara/Windows.Forms/Controls/EnumComboBox.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows.Forms;

namespace Vanara.Windows.Forms
{
	/// <summary>
	/// A combo box that displays the items of an <see cref="Enum"/> type. If the Enum type has a <see cref="FlagsAttribute"/>, then the
	/// drop-down will be checked list of the values.
	/// </summary>
	/// <seealso cref="CustomComboBox"/>
	public class EnumComboBox : CustomComboBox
	{
		private readonly List<ECBItem> items = new List<ECBItem>();
		private readonly Timer timer = new Timer { Interval = 150 };
		private CheckedListBox checkListBox;
		private Type type = null;

		/// <summary>Initializes a new instance of the <see cref="EnumComboBox"/> class.</summary>
		public EnumComboBox() : base()
		{
			base.DropDownStyle = ComboBoxStyle.DropDownList;
			timer.Tick += Timer_Tick;
		}

		/// <summary>Gets or sets the data source for this <see cref="T:System.Windows.Forms.ComboBox"/>.</summary>
		[Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
		public new object DataSource { get => base.DataSource; set => base.DataSource = value; }

		/// <summary>Gets or sets the property to display for this <see cref="T:System.Windows.Forms.ListControl"/>.</summary>
		[Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
		public new string DisplayMember { get => base.DisplayMember; set => base.DisplayMember = value; }

		/// <summary>Gets or sets a value specifying the style of the combo box.</summary>
		/// <PermissionSet><IPermission class="System.Security.Permissions.EnvironmentPermission, mscorlib, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true"/><IPermission class="System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true"/><IPermission class="System.Security.Permissions.SecurityPermission, mscorlib, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Flags="UnmanagedCode, ControlEvidence"/><IPermission class="System.Diagnostics.PerformanceCounterPermission, System, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true"/></PermissionSet>
		[Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
		public new ComboBoxStyle DropDownStyle { get => base.DropDownStyle; set => base.DropDownStyle = value; }

		/// <summary>Gets or sets the Enum type that is used to populate the values of the combo box.</summary>
		/// <value>The enum type string.</value>
		/// <exception cref="ArgumentException">EnumTypeString must be an enumerated type.</exception>
		[DefaultValue(""), Category("Behavior"), Description("The Enum type that is used to populate the values of the combo box.")]
		public string EnumTypeString
		{
			get => type?.FullName ?? "";
			set
			{
				type = FindType(value, true);
				if (type is null || !type.IsEnum)
					throw new ArgumentException("EnumTypeString must be an enumerated type.");

				items.Clear();
				foreach (var item in Enum.GetValues(type))
					items.Add(new ECBItem(item));

				if (type.GetCustomAttributes(typeof(FlagsAttribute), false).Length > 0)
				{
					if (checkListBox == null)
					{
						checkListBox = new CheckedListBox()
						{
							BorderStyle = BorderStyle.None,
							CheckOnClick = true,
							FormattingEnabled = true,
							Location = new System.Drawing.Point(17, 35),
							MultiColumn = false,
							Name = "checkedListBox1",
							Size = new System.Drawing.Size(187, 105),
							TabIndex = 0
						};
						checkListBox.ItemCheck += CheckListBox_ItemCheck;
					}
					checkListBox.Items.Clear();
					checkListBox.Items.AddRange(items.ToArray());
					DropDownControl = checkListBox;
				}
				else
				{
					DropDownControl = null;
					DisplayMember = "Text";
					ValueMember = "Value";
					DataSource = items;
				}
			}
		}

		/// <summary>
		/// Gets or sets the value of the member property specified by the <see cref="P:System.Windows.Forms.ListControl.ValueMember"/> property.
		/// </summary>
		public new object SelectedValue
		{
			get
			{
				var ret = 0L;
				if (!HasFlags)
				{
					ret = Convert.ToInt64(items[SelectedIndex].Value);
				}
				else
				{
					for (var i = 0; i < checkListBox.CheckedItems.Count; i++)
					{
						var o = checkListBox.CheckedItems[i] as ECBItem;
						if (o != null && o.Value is IConvertible)
							try { ret |= Convert.ToInt64(o.Value); } catch { }
					}
				}

				return Convert.ChangeType(ret, GetEnumUnderlyingType(type));
			}
			set
			{
				if (!HasFlags)
					SelectedIndex = items.FindIndex(i => i.Value == value);
				else
				{
					var lval = Convert.ToInt64(value);
					checkListBox.BeginUpdate();
					for (var i = 0; i < checkListBox.Items.Count; i++)
					{
						long? val = null;
						var o = checkListBox.Items[i] as ECBItem;
						if (o != null && o.Value is IConvertible)
							try { val = Convert.ToInt64(o.Value); } catch { }
						checkListBox.SetItemCheckState(i, (val.HasValue && (val.Value & lval) == val.Value) ? CheckState.Checked : CheckState.Unchecked);
					}
					checkListBox.EndUpdate();
				}
			}
		}

		/// <summary>Gets or sets the property to use as the actual value for the items in the <see cref="T:System.Windows.Forms.ListControl"/>.</summary>
		[Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
		public new string ValueMember { get => base.ValueMember; set => base.ValueMember = value; }

		/// <summary>Gets an object representing the collection of the items contained in this <see cref="T:System.Windows.Forms.ComboBox"/>.</summary>
		[Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
		public new ObjectCollection Items => base.Items;

		private bool HasFlags => DropDownControl != null;

		/// <summary>Gets the selected value.</summary>
		/// <typeparam name="T">The type of the value to retrieve.</typeparam>
		/// <returns>The selected value cast to <typeparamref name="T"/>.</returns>
		public T GetSelectedValue<T>() => SelectedValue == null ? default : (T)SelectedValue;

		private static Type GetEnumUnderlyingType(Type eType)
		{
			if (!eType.IsEnum)
				throw new ArgumentException("Must be an Enum type.", nameof(eType));
			var fields = eType.GetFields(System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance);
			if (fields == null || fields.Length != 1)
				throw new ArgumentException("Invalid Enum type.", nameof(eType));
			return fields[0].FieldType;
		}

		private void CheckListBox_ItemCheck(object sender, ItemCheckEventArgs e) => timer.Enabled = true;

		private Type FindType(string name, bool ignoreCase) => AppDomain.CurrentDomain.GetAssemblies().Select(a => a.GetType(name, false, ignoreCase)).Where(t => t != null).FirstOrDefault();

		private string GetFlagText()
		{
			var items = new string[checkListBox.CheckedItems.Count];
			for (var i = 0; i < checkListBox.CheckedItems.Count; i++)
				items[i] = checkListBox.CheckedItems[i].ToString();
			return string.Join(", ", items);
		}

		private void Timer_Tick(object sender, EventArgs e)
		{
			timer.Enabled = false;
			if (HasFlags)
				Text = GetFlagText();
		}

		[Serializable]
		private class ECBItem
		{
			public ECBItem(object value)
			{
				Value = value;
				Text = value.ToString();
				// TODO: Alternatively get text from resource or translation service.
			}

			public string Text { get; set; }
			public object Value { get; set; }

			public override string ToString() => Text;
		}
	}
}