点击展开后背景视图毛玻璃效果
UIBlurEffect *effect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
UIVisualEffectView *effectVIew = [[UIVisualEffectView alloc]initWithEffect:effect];
传入背景视图后(若背景视图是个scrollerView) 设置hideWhileScrolling = Yes 控制悬浮按钮是否要随着背景视图滑动