Question

I’ve written this code to change the serialport name:

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    try
    {    
        serialPort1.PortName = (string)comboBox1.SelectedValue;
    }
    catch (Exception)
    { 
        MessageBox.Show("The SerialPorts's Name Does Not Change !! "); 
    }
}

The result is that I get an Exception. The SerialPort‘s name never changes.

Answer 1

To use the SelectedValue Mr. JaredPar MSFT explained ComboBox SelectedItem, SelectedValue, SelectedWhat???.

I guess, your trying get the PortName not the SelectedValue

Solution:

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedIndex == -1) return;
    if (string.IsNullOrWhiteSpace(comboBox1.Text)) return;
    serialPort1.PortName = comboBox1.Text;
}

or

your trying get the SelectedValue not the PortName

Solution:

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedValue == null) return;
    if (string.IsNullOrWhiteSpace(comboBox1.Text)) return;
    serialPort1.PortName = (int)comboBox1.SelectedValue ;
}

Try to check your properties of ComboBox

 Where: Display Member is your PortName
        Value Member is your PortId or SelectedValue