如图所示, 当QSpinBox的值为最小值的时候, 不是显示这个最小值, 而是显示一个特殊的字符串用以代替这个最小值, 也只是QSpinBox的一个函数调用而已:
void QSpinBox::setSpecialValueText(const QString &specialText);
If set, the spin box will display this text instead of a numeric value whenever the current value is equal to minimum(). Typical use is to indicate that this choice has a special (default) meaning.