How to determine if radioButton.Checked is set programatically or via a mouse click?

this.radioButtonAdd.Checked = true;

savedFlag = modifyingProgrammatically;
modifyingProgrammatically = true;
this.radioButtonAdd.Checked = true;
modifingProgrammatically = savedFlag;

if(modifyingProgramatically) {
    // The event was raised by an assignment within the code.
} else {
    // The event was raised by a user action.
}

radioButton.Tag = "ignore"
radioButton.Checked = true

private void radioButton_CheckedChanged(object sender, EventArgs e)
{
    if (radioButton.Checked)
    {
        // Tag will be null in cases where the user clicks
        if (this.radioButtonAdd.Tag == null)
        {
            // do something
        }
        else
        {
            // swallow action
            // reset Tag
            this.radioButtonAdd.Tag = null;
        }
    }
}

private bool _mouseEvent;
    private void radioButton1_CheckedChanged(object sender, EventArgs e)
    {
        if (_mouseEvent)
            MessageBox.Show("Changed by mouse click.");
        else
            MessageBox.Show("Changed from code.");
    }

    private void radioButton1_MouseClick(object sender, MouseEventArgs e)
    {
        _mouseEvent = false;
    }

    private void radioButton1_MouseDown(object sender, MouseEventArgs e)
    {
        _mouseEvent = true;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // This simulates a change from code vs. a change from
        // a mouse click.
        if (radioButton1.Checked)
            radioButton2.Checked = true;
        else
            radioButton1.Checked = true;
    }