Check if combobox value is empty

Question

I have created a ComboBox with three values. I wanted that a message box opens when no item is selected so I tried this:

if (comboBox1.SelectedItem == null)
{
    MessageBox.Show("Please select a value");
    return;
}

That works fine but only if I click into the field in the combobox. When I dont touch it, the program will start without message box. Whats wrong?

Answer 1

if (string.IsNullOrEmpty(comboBox1.Text)) or if (comboBox1.SelectedIndex == -1)

Answer 2

Use

if (comboBox1.SelectedIndex == -1)
{
   MessageBox.Show("Please select a value");
   return;           
}

Note: SelectedIndex will be set to -1 when SelectedValue is blank ONLY when FormattingEnabled is true. See here.