1、CATextLayer简介

　　CATextLayer快速高效简单地来渲染纯文本、NSAttributedString

/* The text layer provides simple text layout and rendering of plain * or attributed strings. The first line is aligned to the top of the * layer. */NS_ASSUME_NONNULL_BEGINCA_CLASS_AVAILABLE (10.5, 2.0, 9.0, 2.0)@interface CATextLayer : CALayer{@private    struct CATextLayerPrivate *_state;}//渲染的字符串@property(nullable, copy) id string;//字体@property(nullable) CFTypeRef font;//字号@property CGFloat fontSize;//文字颜色@property(nullable) CGColorRef foregroundColor;//是否换行，默认NO@property(getter=isWrapped) BOOL wrapped;//枚举：设置截断模式@property(copy) NSString *truncationMode;//枚举：设置对其模式@property(copy) NSString *alignmentMode;//文字是否像素化，默认NO@property BOOL allowsFontSubpixelQuantization;@end/* Truncation modes. */CA_EXTERN NSString * const kCATruncationNone    //不剪裁，默认CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCATruncationStart   //剪裁开始部分CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCATruncationEnd     //剪裁结束部分CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCATruncationMiddle  //剪裁中间部分CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);/* Alignment modes. */CA_EXTERN NSString * const kCAAlignmentNatural  //默认CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCAAlignmentLeft     //左对齐CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCAAlignmentRight    //右对齐CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCAAlignmentCenter   //居中对齐CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);CA_EXTERN NSString * const kCAAlignmentJustified    //两端对齐CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);NS_ASSUME_NONNULL_END