VC#2008大學(xué)教程的這段代碼不明白

先上代碼

public partial class Form1 : Form
    {
        private MessageBoxIcon iconType;
        private MessageBoxButtons buttonType;
        public Form1()
        {
            InitializeComponent();
        }

        private void buttonType_CheckedChanged(object sender, EventArgs e)
        {
            MessageBox.Show("This is a value", "buttonType", buttonType, iconType, 0, 0);
            if (sender == okRadioButton)
                buttonType = MessageBoxButtons.OK;
            else if (sender == okCancelRadioButton)
                buttonType = MessageBoxButtons.OKCancel;
            else
                buttonType = MessageBoxButtons.RetryCancel;
        }

        private void iconType_checkedChanged(object sender, EventArgs e)
        {
            if (sender == asteriskRadioButton)
                iconType = MessageBoxIcon.Asterisk;
            else if (sender == errorRadioButton)
                iconType = MessageBoxIcon.Error;
            else
                iconType = MessageBoxIcon.Stop;
        }
        private void okRadioButton_CheckedChanged(object sender, EventArgs e)
        {

        }

        

        private void displayButton_Click(object sender, EventArgs e)
        {
            DialogResult result = MessageBox.Show(
                "This is your Custom MessageBox.", "Custon MessageBox", buttonType, iconType, 0, 0
                );
        }
    }

這里面的buttonType_checkedChanged和iconType_checkedChanged哪里來的啊，完全沒有用么