UIImageView设置圆角时产生UI不流畅的解决方案

来源:互联网 发布:永恒之塔数据库4.7 编辑:程序博客网 时间:2024/03/29 06:52

在做一个NavigationController push 子页面时,发现push和pop时很卡,研究了一大阵子后,发现在子页面里影响UI流畅的只有UIImageView的圆角设置;然后我就关闭了圆角,重新运行果然流畅多了。但是产品的需求必须加圆角,没办法,去stackoverflow找方案,发现方法都大同小异,只不过是绘制上做一些优化。后来查看layer的头文件,最后找到了一个牛B的属性:

/* When true, the layer is rendered as a bitmap in its local coordinate * space ("rasterized"), then the bitmap is composited into the * destination (with the minificationFilter and magnificationFilter * properties of the layer applied if the bitmap needs scaling). * Rasterization occurs after the layer's filters and shadow effects * are applied, but before the opacity modulation. As an implementation * detail the rendering engine may attempt to cache and reuse the * bitmap from one frame to the next. (Whether it does or not will have * no affect on the rendered output.) * * When false the layer is composited directly into the destination * whenever possible (however, certain features of the compositing * model may force rasterization, e.g. adding filters). * * Defaults to NO. Animatable. */@property BOOL shouldRasterize;/* The scale at which the layer will be rasterized (when the * shouldRasterize property has been set to YES) relative to the * coordinate space of the layer. Defaults to one. Animatable. */@property CGFloat rasterizationScale;
当shouldRasterize设成true时,layer被渲染成一个bitmap,并缓存起来,等下次使用时不会再重新去渲染了。实现圆角本身就是在做颜色混合(blending),如果每次页面出来时都blending,消耗太大,这时shouldRasterize = yes,下次就只是简单的从渲染引擎的cache里读取那张bitmap,节约系统资源。

额外收获:如果在滚动tableView时,每次都执行圆角设置,肯定会阻塞UI,设置这个将会使滑动更加流畅。

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