1. 設(shè)置圓角

-(UIImage *)avaterImageWithImage:(UIImage *)image size:(CGSize)size backColor:(UIColor *)backColor{
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContextWithOptions(size, true, 0);
    //0.背景填充
    [backColor setFill];
    UIRectFill(rect);
    //1.實例化圓形路徑
    UIBezierPath *path =  [UIBezierPath bezierPathWithOvalInRect:rect];
    [path addClip];
    //2.在指定區(qū)域拉伸屏幕
    [image drawInRect:rect];
    //3.繪制內(nèi)切的圓形
    [[UIColor darkGrayColor] setStroke];
    path.lineWidth = 2;
    [path stroke];
    //4.獲取image
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    //5.關(guān)閉上下文
    UIGraphicsEndImageContext();
    return result;
}

2. 柵格化

  缺點耗電會增加
//異步繪制
    self.layer.drawsAsynchronously = YES;
    //柵格化
    self.layer.shouldRasterize = YES;
    //指定分辨率
    self.layer.rasterizationScale = [UIScreen mainScreen].scale;

3.cell里不使用block
delegate運行成本低，block成本很高。
cell里的回調(diào)事件通過delegate處理，cell由于復(fù)用會反復(fù)執(zhí)行賦值操作。