Getsuyodev, Programming is mainly used when constructing an application. Programming requires knowledge of application domains, algorithms, and programming language expertise. Programming can be developed in different logic based on developer knowledge.

C# ComboBox Control



C# controls are located in the Toolbox of the development environment, and you use them to create objects on a form with a simple series of mouse clicks and dragging motions. A ComboBox displays a text box combined with a ListBox, which enables the user to select items from the list or enter a new value.

The user can type a value in the text field or click the button to display a drop-down list. You can add individual objects with the Add method. You can delete items with the Remove method or clear the entire list with the Clear method.

How to add an item to Combobox

comboBox1.Items.Add("Sunday");
comboBox1.Items.Add("Monday");
comboBox1.Items.Add("Tuesday");

ComboBox SelectedItem

How to retrieve the value from ComboBox

If you want to retrieve the displayed item to a string variable, you can code like this

string var;
var = comboBox1.Text;
			Or
var item = this.comboBox1.GetItemText(this.comboBox1.SelectedItem);
MessageBox.Show(item);

How to remove an item from ComboBox

You can remove items from a Combobox in two ways. You can remove an item at the specified index or giving a specified item by name.

comboBox1.Items.RemoveAt(1);

The above code will remove the second item from the Combobox.

comboBox1.Items.Remove("Friday");

The above code will remove the item “Friday” from the Combobox.

DropDownStyle

The DropDownStyle property specifies whether the list is always displayed or whether the list is displayed in a drop-down. The DropDownStyle property also specifies whether the text portion can be edited.

comboBox1.DropDownStyle = ComboBoxStyle.DropDown;

ComboBox Selected Value

How to set the selected item in a ComboBox

You can display selected item in a Combobox in two ways.

comboBox1.Items.Add("test1");
comboBox1.Items.Add("test2");
comboBox1.Items.Add("test3");
comboBox1.SelectedItem = "test3";
or
comboBox1.SelectedIndex = comboBox1.FindStringExact("test3");

ComboBox DataSource Property

How to populate a combo box with a DataSet?

You can Programmatically Binding DataSource to ComboBox in a simple way.

Consider an SQL string like …”select au_id,au_lname from authors”;

Make a data source and bind it like the following…

comboBox1.DataSource = ds.Tables[0];
comboBox1.ValueMember = "au_id";
comboBox1.DisplayMember = "au_lname";

Combobox SelectedIndexChanged event

The SelectedIndexChanged event of a Combobox fire when you change the selected item in a Combobox. If you want to do something when you change the selection, you can write the program on the SelectedIndexChanged event. From the following code, you can understand how to set values in the SelectedIndexChanged event of a Combobox. Drag and drop two Combobox on the Form and copy and paste the following source code.

using System;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            comboBox1.Items.Add("weekdays");
            comboBox1.Items.Add("year");
        }
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            comboBox2.Items.Clear();
            if (comboBox1.SelectedItem == "weekdays")
            {
                comboBox2.Items.Add("Sunday");
                comboBox2.Items.Add("Monday");
                comboBox2.Items.Add("Tuesday");
            }
            else if (comboBox1.SelectedItem == "year")
            {
                comboBox2.Items.Add("2012");
                comboBox2.Items.Add("2013");
                comboBox2.Items.Add("2014");
            }
        }
    }
}

ComboBox Default Value

How to set a default value for a Combo Box

You can set Combobox default value by using SelectedIndex property

comboBox1.SelectedIndex = 6;

Above code set 6th item as Combobox default value

ComboBox readonly

How to make a Combobox read-only

You can make a ComboBox readonly, that means a user cannot write in a combo box, but he can select the given items, in two ways. By default, DropDownStyle property of a Combobox is DropDown. In this case, the user can enter values to Combobox. When you change the DropDownStyle property to DropDownList, the Combobox will become read-only, and the user can not enter values to Combobox. The second method, if you want the Combobox completely read-only, you can set comboBox1.Enabled = false.

ComboBox Example

The following C# source code adds seven days in a week to a combo box while load event of a Windows Form and int Button click event it displays the selected text in the Combo Box.

using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            comboBox1.Items.Add("Sunday");
            comboBox1.Items.Add("Monday");
            comboBox1.Items.Add("Tuesday");
            comboBox1.Items.Add("wednesday");
            comboBox1.Items.Add("Thursday");
            comboBox1.Items.Add("Friday");
            comboBox1.Items.Add("Saturday");
			comboBox1.SelectedIndex = comboBox1.FindStringExact("Sunday");

        }

        private void button1_Click(object sender, EventArgs e)
        {
            string var;
            var = comboBox1.Text;
            MessageBox.Show(var);
        }
    }
}

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