如何判断comboBox当前值为空？

Question

RT，如何判断呢？

Answer 1

   if (comboBox1.SelectedValue == null)
            { 
            
            }

Answer 2

if (comboBox1.SelectedItem==null)
            { 
            
            }

Answer 3

 if (comboBox1.SelectedItem == null)
            {
                MessageBox.Show("为空");
            }

Answer 4

 private void btnSave_Click(object sender, EventArgs e)
        {
            if (cobType.SelectedValue == null)
            {
                cobType.Focus();
            }
            else
            {
                if (txtAddress.Text == string.Empty)
                {
                    txtAddress.Focus();
                }
                else
                {
                    if (txtArea.Text == string.Empty)
                    {
                        txtArea.Focus();
                    }
                 }
            }
        }
为什么焦点总是第一个呢？

Answer 5

不好意思  第一个写错了 是comboBox1.SelectedItem==null