ComboBox Controls
The ComboBox control is used to save space on a dialog because the only part
of the combo box that is permanently visible are the text box and button parts
of the control. When the user clicks the arrow button to the right of the text
box, a list box unfolds in which the user can make a selection. As soon as he or
she does so, the list box disappears and the display returns to normal.
As the name implies, a combo box combines a number of controls,
to be specific the TextBox, Button, and ListBox controls. Unlike the ListBox, it
is never possible to select more than one item in the list of items contained in
a ComboBox and it is optionally possible to type new entries in the list in the
TextBox part of the ComboBox.
ComboBox Properties
|
Name |
Availability |
Description |
| DropDownStyle |
Read/Write |
A combo box can be displayed with three
different styles:
q DropDown: The user can edit the text box part of the control, and must
click the arrow button to display the list part of the control.
q Simple: Same as DropDown, except that the list part of the control is
always visible, much like a normal ListBox.
q DropDownList: The user cannot edit the text box part of the control, and
must click the arrow button to display the list part of the control. |
| DroppedDown |
Read/Write |
Indicates whether the list part of the control
is dropped down or not. If you set this property to true, the list will
unfold. |
| Items |
Read-only |
This property is a collection, which contains
all the items in the list contained in the combo box. |
| MaxLength |
Read/Write |
By setting this property to anything other than
zero, you control the maximum number of characters it is possible to enter
into the text box part of the control. |
| SelectedIndex |
Read/Write |
Indicates the index of the currently selected
item in the list. |
| SelectedItem |
Read/Write |
Indicates the item that is currently selected in
the list. |
| SelectedText |
Read/Write |
Represents the text that is selected in the text
box part of the control. |
| SelectionStart |
Read/Write |
In the text box part of the control, this
property represents the index of the first character that
is selected. |
| SelectionLength |
Read/Write |
The length of the text selected in the text box
part of the control. |
| Sorted |
Read/Write |
Set this property to true to make the control
sort the items in the list portion alphabetically. |
| Text |
Read/Write |
If you set this property to null, any selection
in the list portion of the control is removed. If you set it to a value,
which exists in the list part of the control, that value is selected. If the
value doesn't exist in the list, the text is simply shown in the text
portion. |
ComboBox Events
|
Name |
Description |
| DropDown |
Occurs when the list portion of the control is dropped down. |
| SelectedIndexChanged |
Occurs when the selection in the list portion of the
control changed. |
| KeyDown, KeyPress, KeyUp |
These events occur when a key is pressed while the text
portion of the control has focus. Please refer to the descriptions of the
events in the text box section earlier in this chapter. |
| TextChanged |
Occurs when the Text property changes |
ComboBox Text Example
In following
image i have designed a window form for saving the address of user. Make design
of your application in following image manner and change properties according to
you.
In following figure for selecting country i have used ComboBox for selecting
country and after that he/she will get the name of corresponding state name of
that country he/she selected.
Code for Combobox1 to add the items in Combobox2.
Write following code on Combobox1 selected index change
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
comboBox2.Items.Clear();
comboBox2.Enabled = true;
if (comboBox1.SelectedItem.ToString() == "India")
{
comboBox2.Items.Add("NewDelhi");
comboBox2.Items.Add("Chennai");
comboBox2.Items.Add("Banglore");
comboBox2.Items.Add("Mumbai");
}
else if (comboBox1.SelectedItem.ToString() == "Australia")
{
comboBox2.Items.Add("Sydney");
comboBox2.Items.Add("Johnsberg");
comboBox2.Items.Add("Perth");
comboBox2.Items.Add("Melborn");
}
else if (comboBox1.SelectedItem.ToString() == "United States")
{
comboBox2.Items.Add("NewYork");
comboBox2.Items.Add("Los Ageles");
comboBox2.Items.Add("California");
comboBox2.Items.Add("LosBegas");
}
}
|
After that choosing State name he/she will get the location in ComboBox 3.
Like in following figure.
Code for ComboBox2 is given below write that code on
Combobox2 Selected Index Changed
private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
{
comboBox3.Items.Clear();
comboBox3.Enabled = true;
if (comboBox2.SelectedItem.ToString() == "NewDelhi")
{
comboBox3.Items.Add("East Delhi");
comboBox3.Items.Add("West Delhi");
comboBox3.Items.Add("North Delhi");
comboBox3.Items.Add("South Delhi");
}
else if (comboBox2.SelectedItem.ToString() == "Chennai")
{
comboBox3.Items.Add("Chennai");
}
else if (comboBox2.SelectedItem.ToString() == "Mumbai")
{
comboBox3.Items.Add("Mumbai");
comboBox3.Items.Add("Navi Mumbai");
}
else if (comboBox2.SelectedItem.ToString() == "Banglore")
{
comboBox3.Items.Add("Banglore");
}
else if (comboBox2.SelectedItem.ToString() == "Johnsberg")
{
comboBox3.Items.Add("Johnsberg");
}
else if (comboBox2.SelectedItem.ToString() == "Sydney")
{
comboBox3.Items.Add("Sydney");
}
else if (comboBox2.SelectedItem.ToString() == "Perth")
{
comboBox3.Items.Add("Perth");
}
}
|
Code for Save Button Click
private void button1_Click(object sender, EventArgs e)
{
string output;
output = "Name: " + this.textBox1.Text + "\r\n";
output += "Address : " + this.textBox2.Text + "\r\n";
output += " " + this.textBox3.Text + "\r\n";
output += " " + this.comboBox3.Text+ "\r\n";
output += " " + this.comboBox2.Text + "\r\n";
output += "Country: " + this.comboBox1.Text + "\r\n";
textBox4.Text = output;
}
|
Final you will get output Like this.
Tolal:1 Click:
1
Username :sangeetha
Comments :To click menu form show should comobox always focus how
URL :http://r4r.co.in/c1/01/tutorial/csharp/ComboBox.shtml
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