Question: I have a combo box and textbox in form, (in windows form platform), the textbox visible is false by default, I want to show (visible=true) the the textbox when the specific item of combo box selected.

which event of combobox is suitable for this work!

Answer: 
if you're depending on a fixed index in the combo box items use SelectedIndexChange event

```
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedIndex == yourindex)
        textBox1.Visible = true; 
    else
        textBox1.Visible = false; 
}

```

if you're depending on combo box selected item value use SelectedValueChanged event

```
private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedValue.ToString() == "yourvalue")
        textBox1.Visible = true;
    else
        textBox1.Visible = false; 
}

```
This Code will definitely help you.

```
if (comboBox2.Text.ToString() == "Desired Value")
     comboBox1.Visible = true;
else
     comboBox1.Visible = false;

```