public void UpdateDisplay()
{
//Enhance: when you go to another book, currently this shows briefly before we get a
//chance to select how to display it. I haven't found any existing event I can use
//to hide it first.
//What we're doing here is unusual; we want to always get clicks, so that if the button is
//disabled, we can at least tell the user *why* its disabled.
//Whereas this class has an ImageNormal and ImageDisabled, in order to never be truly
//disabled, we don't use that. The button always thinks its in the "Normal" (enabled) state.
//But we switch its "normal" image and forecolor in order to get this "soft disabled" state
_addPageButton.ImageNormal = _model.CanAddPages ? Resources.AddPageButton : Resources.AddPageButtonDisabled;
_addPageButton.ForeColor = _model.CanAddPages ? Palette.BloomRed : Color.FromArgb(87,87,87);
}