利用系統(tǒng)自帶的UIVisualEffectView類來創(chuàng)建毛玻璃效果，并設置為self.bouns來覆蓋整個視圖，詳細關于UIVisualEffectView的介紹請看《最近開發(fā)遇到的一些UI問題》

UIVisualEffectView *bgView = [[UIVisualEffectView alloc] initWithEffect:[UIBlurEffect effectWithStyle:UIBlurEffectStyleLight]];

bgView.alpha = 0.9f;

bgView.frame = CGRectMake(0, 0, WIDTH, HEIGHT);

bgView.layer.cornerRadius = BALL_RADIUS / 2;

bgView.clipsToBounds = YES;

[self addSubview:bgView];