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:

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