整体介绍
CATextLayer是CALayer的子类，它以图层的形式包含了UILabel几乎所有的绘制特性，并且额外提供了一些新的特性。
同样，CATextLayer也要比UILabel渲染得快得多。很少有人知道在iOS 6及之前的版本，UILabel其实是通过WebKit来实现绘制的，这样就造成了当有很多文字的时候就会有极大的性能压力。而CATextLayer使用了Core text，并且渲染得非常快。
/* CoreAnimation - CATextLayer.h
Copyright (c) 2006-2016, Apple Inc.
All rights reserved. */
#import <QuartzCore/CALayer.h>
/* 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_BEGIN
CA_CLASS_AVAILABLE (10.5, 2.0, 9.0, 2.0)
@interface CATextLayer : CALayer
{
@private
struct CATextLayerPrivate *_state;
}
/* The text to be rendered, should be either an NSString or an
* NSAttributedString. Defaults to nil. */
// 文本呈现，可以是一个NSString或者NSAttributedString；默认为nil
@property(nullable, copy) id string;
/* The font to use, currently may be either a CTFontRef, a CGFontRef,
* or a string naming the font. Defaults to the Helvetica font. Only
* used when the `string' property is not an NSAttributedString. */
// 字体使用，可能是一个CTFontRef，一个CGFontRef或者一个字符串命名体，默认为Helvetica字体；仅当string不是一个NSAttributedString的时候使用
@property(nullable) CFTypeRef font;
/* The font size. Defaults to 36. Only used when the `string' property
* is not an NSAttributedString. Animatable (Mac OS X 10.6 and later.) */
// 字号，默认36 仅当string不是一个NSAttributedString的时候使用；
@property CGFloat fontSize;
/* The color object used to draw the text. Defaults to opaque white.
* Only used when the `string' property is not an NSAttributedString.
* Animatable (Mac OS X 10.6 and later.) */
// 用来绘制文本的颜色，默认为不透明的白色；仅当string不是一个NSAttributedString的时候使用；
@property(nullable) CGColorRef foregroundColor;
/* When true the string is wrapped to fit within the layer bounds.
* Defaults to NO.*/
// 文本自适应图层大小，默认是NO
@property(getter=isWrapped) BOOL wrapped;
/* Describes how the string is truncated to fit within the layer
* bounds. The possible options are `none', `start', `middle' and
* `end'. Defaults to `none'. */
// 描述如何将字符串截断以适应图层大小，设置缩短的部位，可选择没有，开始，中间，和结束
@property(copy) NSString *truncationMode;
/* Describes how individual lines of text are aligned within the layer
* bounds. The possible options are `natural', `left', `right',
* `center' and `justified'. Defaults to `natural'. */
// 对齐方式
@property(copy) NSString *alignmentMode;
/* Sets allowsFontSubpixelQuantization parameter of CGContextRef
* passed to the -drawInContext: method. Defaults to NO. */
// 默认NO
@property BOOL allowsFontSubpixelQuantization;
@end
/* Truncation modes. */
CA_EXTERN NSString * const kCATruncationNone
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCATruncationStart
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCATruncationEnd
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCATruncationMiddle
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
/* Alignment modes. */
CA_EXTERN NSString * const kCAAlignmentNatural
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCAAlignmentLeft
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCAAlignmentRight
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCAAlignmentCenter
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
CA_EXTERN NSString * const kCAAlignmentJustified
CA_AVAILABLE_STARTING (10.5, 3.2, 9.0, 2.0);
NS_ASSUME_NONNULL_END
应用
CATextLayer *textLayer = [CATextLayer layer];
textLayer.string = @"test";
textLayer.bounds = CGRectMake(0, 0, 200, 20);
textLayer.font = @"HiraKakuProN-W3"; // 字体的名字 不是 UIFont
textLayer.fontSize = 12.f;//字体的大小
// UIFont *font = [UIFont systemFontOfSize:14];
// CFStringRef fontCFString = (__bridge CFStringRef)font.fontName;
// CGFontRef fontRef = CGFontCreateWithFontName(fontCFString);
// textLayer.font = fontRef;
// textLayer.fontSize = font.pointSize;
// CGFontRelease(fontRef); //与CFRelease的功能相当 当字体的null的时候不会引起程序出错
textLayer.wrapped = YES;
textLayer.alignmentMode = kCAAlignmentCenter;
textLayer.position = CGPointMake(100, 100);
textLayer.contentsScale = [UIScreen mainScreen].scale;
textLayer.foregroundColor =[UIColor redColor].CGColor;
[self.view.layer addSublayer:textLayer];