Implementing MultiSelectionComboBox

The MultiSelectionComboBox is a WinForms ComboBox control that supports multiple item selection and auto-suggestion. Selected items can be displayed as removable tag chips (VisualItem mode), comma-separated text (Delimiter mode), or single-value (Normal mode). It supports data binding via DataSource/DisplayMember/ValueMember, Office-style visual themes, grouping, and a rich event model.

When to Use This Skill

• Adding a multi-select dropdown to a Windows Forms application
• Displaying selected values as tag chips with close buttons
• Binding the combo box to a DataTable, DataView, or ArrayList
• Configuring auto-suggestion behavior (AutoSuggestMode)
• Grouping dropdown items by initial character
• Styling the drop-down list or visual item tags
• Handling selection change and visual item collection events

Documentation and Navigation Guide

Getting Started

📄 Read: references/getting-started.md

• Assembly references and NuGet package setup
• Adding the control via Designer or code-behind
• Namespace imports (C# and VB.NET)
• Basic instantiation with ButtonStyle, UseVisualStyle, and Size
• Minimal working example

Display Modes & Visual Item Input

📄 Read: references/display-modes-and-visual-items.md

• DisplayMode.VisualItem — tag chips with remove buttons
• DisplayMode.DelimiterMode — comma-separated text
• DisplayMode.NormalMode — single-value selection
• AutoSizeMode: Vertical, Horizontal, None
• VisualItemInputMode: DisplayMemberMode, ValueMemberMode, VisualItemMode
• Delimiter character customization

Data Binding

📄 Read: references/data-binding.md

• Binding to ArrayList, DataView, and DataTable
• DataSource, DisplayMember, ValueMember properties
• Complete external data source binding example
• DataSourceChanged event handling

Styling & Customization

📄 Read: references/styling-and-customization.md

• Visual styles: Default, Office2016Colorful, Office2016White, Office2016Black, Office2016DarkGray
• Drop-down styling: ShowCheckBox, group header colors, item/drop-down dimensions
• Visual item tag colors: BackColor, ForeColor, SelectionColor, BorderColor
• Grouping: ShowGroups, runtime enable/disable
• Auto-suggestion modes: Begin, Match, Disabled

Events & Advanced Features

📄 Read: references/events-and-advanced-features.md

• SelectedItemCollectionChanged — when the selected items change
• VisualItemCollectionChanged — when visual item tags are added/removed
• AutoSizeModeChanged, DataSourceChanged, DropDown events
• Detecting VisualItemCollection modifications at runtime

Quick Start

using Syncfusion.Windows.Forms.Tools;
using Syncfusion.Windows.Forms;

// Create and configure the control
var combo = new MultiSelectionComboBox();
combo.ButtonStyle = ButtonAppearance.Metro;
combo.UseVisualStyle = true;
combo.Size = new System.Drawing.Size(250, 30);
combo.DisplayMode = DisplayMode.VisualItem;

// Add items manually
combo.Items.AddRange(new object[] { "Apple", "Banana", "Cherry", "Date", "Elderberry" });

this.Controls.Add(combo);

Imports Syncfusion.Windows.Forms.Tools
Imports Syncfusion.Windows.Forms

Dim combo As New MultiSelectionComboBox()
combo.ButtonStyle = ButtonAppearance.Metro
combo.UseVisualStyle = True
combo.Size = New System.Drawing.Size(250, 30)
combo.DisplayMode = DisplayMode.VisualItem
combo.Items.AddRange(New Object() {"Apple", "Banana", "Cherry"})
Me.Controls.Add(combo)

Common Patterns

Bind to a DataTable and display as tag chips

DataTable dt = new DataTable();
dt.Columns.Add("ID");
dt.Columns.Add("Name");
dt.Rows.Add("1", "Alice");
dt.Rows.Add("2", "Bob");
dt.Rows.Add("3", "Carol");

combo.DataSource = dt;
combo.DisplayMember = "Name";
combo.ValueMember = "ID";
combo.DisplayMode = DisplayMode.VisualItem;

React to selection changes

combo.SelectedItemCollectionChanged += (sender, e) =>
{
    if (e.Action == Actions.Added)
        Console.WriteLine("Added: " + e.SelectedItems[0]);
    else
        Console.WriteLine("Removed: " + e.SelectedItems[0]);
};

Apply Office 2016 Colorful theme

combo.Style = MultiSelectionComboBoxStyle.Office2016Colorful;

Key Properties

Property	Purpose
DisplayMode	VisualItem / DelimiterMode / NormalMode
AutoSuggestMode	Begin / Match / Disabled
AutoSizeMode	Vertical / Horizontal / None
ShowCheckBox	Show checkboxes in the dropdown
ShowGroups	Group items by initial character
DelimiterChar	Separator character (Delimiter mode)
DataSource	Bind to ArrayList, DataView, DataTable
DisplayMember	Property name shown in the control
ValueMember	Property used as the actual value
Style	Visual theme (Office2016Colorful, etc.)
VisualItemInputMode	DisplayMemberMode / ValueMemberMode / VisualItemMode