ComboBox In C#

The new ComboBox with background and foreground looks like Figure 4.

Figure 4

ComboBox Items

The Items property is used to add and access items in a ComboBox. We can add items to a ComboBox at design-time from Properties Window by clicking on Items Collection as you can see in Figure 5.

Figure 5

When you click on the Collections, the String Collection Editor window will pop up where you can type strings. Each line added to this collection will become a ComboBox item. I add four items as you can see from Figure 6.

Figure 6

The ComboBox looks like Figure 7.

Figure 7

Alternatively, you can add same items at run-time by using the following code snippet.

comboBox1.Items.Add("Mahesh Chand");  
comboBox1.Items.Add("Mike Gold");  
comboBox1.Items.Add("Praveen Kumar");  
comboBox1.Items.Add("Raj Beniwal"); 

Getting All Items

To get all items of a control, we use Items property that is a collection of items.

The following code snippet loops through all items and adds item contents to a StringBuilder and displays in a MessageBox.

private void GetItemsButton_Click(object sender, EventArgs e)  
{  
    StringBuilder sb = new StringBuilder();  
    foreach (string name in Combo1.Items)  
    {  
        sb.Append(name);  
        sb.Append(" ");  
    }  
    MessageBox.Show(sb.ToString());  
}

Selected Text and Item

Text property is used to set and get text of a ComboBox. The following code snippet sets and gets current text of a ComboBox.

comboBox1.Text = "Mahesh Chand";  
MessageBox.Show(comboBox1.Text);

We can also get text associated with currently selected item by using Items property.

string selectedItem = comboBox1.Items[comboBox1.SelectedIndex].ToString();

Why the value of ComboBox.SelectedText is Empty?

SelectedText property gets and sets the selected text in a ComboBox only when a ComboBox has focus on it. If the focus moves away from a ComboBox, the value of SelectedText will be an empty string. To get current text in a ComboBox when it does not have focus, use Text property.

DataSource

A ComboBox can be used to bind to a collection of items. DataSource property is used to get and set a data source to a ComboBox. The data source can be a collection or object that implements IList interface such as an array, a collection, or a DataSet.

The following code snippet binds an enumeration converted to an array to a ComboBox.

comboBox1.DataSource = System.Enum.GetValues(typeof(ComboBoxStyle));  

DropDownStyle

DropDownStyle property is used to gets and sets the style of a ComboBox. It is a type of ComboBoxStyle enumeration.

The ComboBoxStyle enumeration has following three values.

• Simple - List is always visible and the text portion is editable.
• DropDown – List is displayed by clicking the down arrow and that the text portion is editable.
• DropDownList - List is displayed by clicking the down arrow and that the text portion is not editable.

The following code snippet sets the DropDownStyle property of a ComboBox to DropDownList.

comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;  

DroppedDown

If set true, the dropped down portion of the ComboBox is displayed. By default, this value is false.

Sorting Items

The Sorted property set to true, the ComboBox items are sorted. The following code snippet sorts the ComboBox items.

comboBox1.Sorted = true; 

Find Items

FindString method is used to find a string or substring in a ComboBox. The following code snippet finds a string in a ComboBox and selects it if found.

private void FindButton_Click(object sender, EventArgs e)  
{  
   int index = comboBox1.FindString(textBox1.Text);  
   if (index < 0)  
   {  
      MessageBox.Show("Item not found.");  
      textBox1.Text = String.Empty;  
   }  
   else  
   {  
      comboBox1.SelectedIndex = index;  
   }  
}

ComboBox SelectedIndexChanged Event Hander

CheckedChanged and CheckStateChanged are two important events for a ComboBox control. The CheckedChanged event occurs when the value of the Checked property changes. The CheckStateChanged event occurs when the value of the CheckState property changes.

To add these event handlers, you go to Events window and double click on CheckedChanged and CheckedStateChanged events as you can see in Figure 8.

Figure 8

The following code snippet defines and implements these events and their respective event handlers.

comboBox1.SelectedIndexChanged += new System.EventHandler(ComboBox1_SelectedIndexChanged);  
private void ComboBox1_SelectedIndexChanged(object sender,System.EventArgs e)  
{  
   MessageBox.Show(comboBox1.Text);  
}

Summary

In this article, we discussed discuss how to create a ComboBox control in Windows Forms at design-time as well as run-time. After that, we discussed how to use its various properties and methods to build real world applications.