ComboBox in C#

In Windows Forms, ComboBox provides two different features in a single control, it means ComboBox works as both TextBox and ListBox. In ComboBox, only one item is displayed at a time and the rest of the items are present in the drop-down menu. The ComboBox is a class in C# and defined under System.Windows.Forms Namespace. You can create ComboBox using the two different ways:

1. Design-Time: It is the easiest method to create a ComboBox control using the following steps:

• Step 1: Create a windows form as shown in the below image:
  Visual Studio -> File -> New -> Project -> WindowsFormApp
  
• Step 2: Drag the ComboBox control from the ToolBox and drop it on the windows form. You are allowed to place a ComboBox control anywhere on the windows form according to your need.
  
• Step 3: After drag and drop you will go to the properties of the ComboBox control to set the properties of the ComboBox according to your need.
  
  
  
  

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Run-Time: It is a little bit trickier than the above method. In this method, you can set create your own ComboBox control using the ComboBox class. Steps to create a dynamic ComboBox:

• Step 1: Create a combobox using the ComboBox() constructor is provided by the ComboBox class.

  // Creating combobox using ComboBox class
  ComboBox mybox = new ComboBox();
  

• Step 2: After creating ComboBox, set the properties of the ComboBox provided by the ComboBox class.

  // Set the location of the ComboBox 
  mybox.Location = new Point(327, 77);
  
  // Set the size of the ComboBox
  mybox.Size = new Size(216, 26);
  
  // Add items in the ComboBox
  mybox.Items.Add("C#");
  mybox.Items.Add("Java");
  mybox.Items.Add("Scala");
  mybox.Items.Add("C");
  mybox.Items.Add("C++");
  

• Step 3: And last add this ComboBox control to form using Add() method.

  // Add this ComboBox to the form
  this.Controls.Add(mybox);
  

  Example:

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  using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms;    namespace WindowsFormsApp18 {    public partial class Form1 : Form {        public Form1()     {         InitializeComponent();     }        private void Form1_Load(object sender, EventArgs e)     {         // Creating and setting the properties of label         Label l = new Label();         l.Location = new Point(122, 80);         l.AutoSize = true;         l.Text = "Select Programming Language";            // Adding this label to the form         this.Controls.Add(l);            // Creating and setting the properties of comboBox         ComboBox mybox = new ComboBox();         mybox.Location = new Point(327, 77);         mybox.Size = new Size(216, 26);         mybox.Items.Add("C#");         mybox.Items.Add("Java");         mybox.Items.Add("Scala");         mybox.Items.Add("C");         mybox.Items.Add("C++");            // Adding this ComboBox to the form         this.Controls.Add(mybox);     } } }

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  Output:

  

Important Properties of the ComboBox

Property	Description
BackColor	This property is used to set the background color for the ComboBox control.
DropDownHeight	This property is used to set the height in pixels of the drop-down portion of the ComboBox control.
DropDownStyle	This property is used to set a value specifying the style of the ComboBox control.
DropDownWidth	This property is used to set the width of the of the drop-down portion of a ComboBox control.
Font	This property is used to set the font of the text displayed by the ComboBox control.
ForeColor	This property is used to set the foreground color of the ComboBox control.
Height	This property is used to set the height of the ComboBox control.
Items	This property is used to get an object representing the collection of the items contained in this ComboBox control.
MaxDropDownItems	This property is used to set the maximum number of items to be shown in the drop-down portion of the ComboBox control.
MaxLength	This property is used to set the number of characters a user can type into the ComboBox control.
Name	This property is used to set the name of the ComboBox control.
SelectedItem	This property is used to set currently selected item in the ComboBox.
Size	This property is used to set the height and width of the ComboBox control.
Sorted	This property is used to set a value indicating whether the items in the combo box are sorted.
Text	This property is used to set the text associated with this ComboBox control.
Visible	This property is used to set a value indicating whether the control and all its child controls are displayed.

Important Events

Event	Description
Click	This event occur when the ComboBox control is clicked.
DragDrop	This event occur when a drag-and-drop operation is completed.
DropDown	This event occur when the drop-down portion of a ComboBox is shown.
DropDownClosed	This event occur when the drop-down portion of the ComboBox is no longer visible.
DropDownStyleChanged	This event occur when the DropDownStyle property has changed.
Leave	This event occur when the input focus leaves the ComboBox control.
MouseClick	This event occur when the ComboBox control is clicked by the mouse.
MouseDoubleClick	This event occur when the ComboBox control is double clicked by the mouse.
MouseDown	This event occur when the mouse pointer is over the ComboBox control and a mouse button is pressed.
MouseEnter	This event occur when the mouse pointer enters the ComboBox control.
MouseHover	This event occur when the mouse pointer rests on the ComboBox control.
SelectedIndexChanged	This event occur when the SelectedIndex property has changed.

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