How to Add Items in 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. You are allowed to a list or collection of elements in your ComboBox by using Items Property. You can set this property using two different methods:

1. Design-Time: It is the easiest method to add the items in the 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 add the collection of elements in the ComboBox.
  

  Output:
  

2. Run-Time: It is a little bit trickier than the above method. In this method, you can add the list of elements in the ComboBox programmatically with the help of given syntax:

public System.Windows.Forms.ComboBox.ObjectCollection Items { get; }

Here, the ComboBox.ObjectCollection indicates the elements present in the ComboBox. Following steps are used to add the elements in the 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, add the elements in the ComboBox.

  // Adding elements in the combobox
  mybox.Items.Add(230);
  mybox.Items.Add(231);
  mybox.Items.Add(232);
  mybox.Items.Add(233);
  mybox.Items.Add(234);;
  

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

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

  Example:

  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 WindowsFormsApp11 {
  
  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(222, 80);
          l.Size = new Size(99, 18);
          l.Text = "Select Your id";
  
          // 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.Name = "My_Cobo_Box";
          mybox.Items.Add(230);
          mybox.Items.Add(231);
          mybox.Items.Add(232);
          mybox.Items.Add(233);
          mybox.Items.Add(234);
  
          // Adding this ComboBox to the form
          this.Controls.Add(mybox);
      }
  }
  }

  Output: