enabled和userInteractionEnabled差异

UIButton *btn = [[UIButton alloc] init];
    btn.enabled = NO;
    btn.userInteractionEnabled = NO;

    UIControlStateNormal;
    UIControlStateHighlighted;
    // 注意点: 只有设置按钮的enabled = NO才能够有达到这个状态(UIControlStateDisabled);
    UIControlStateDisabled;