CALayer 知识：创建带阴影效果的圆角图片图层和创建自定义绘画内容图层

效果如下：

KMLayerDelegate.h

 #import <UIKit/UIKit.h>

 @interface KMLayerDelegate : NSObject

 @end

KMLayerDelegate.m

 #import "KMLayerDelegate.h"

 @implementation KMLayerDelegate

 /**
  *  根据角度，获取对应的弧度
  *
  *  @param degree 角度
  *
  *  @return 对应的弧度
  */
 static inline double radian(double degree) {
     return degree * M_PI/;
 }

 /**
  *  绘画着色模式内容；绘画预定宽高大小的单元格，每个单元格包含两个半圆，分别为『左上角的上半圆』和『右下边的下半圆』
  *
  *  @param info    信息
  *  @param context 上下文
  */
 void drawColoredPattern(void *info, CGContextRef context) {
     CGColorRef dotColor = [UIColor colorWithHue:0.0 saturation:0.0 brightness:0.0 alpha:0.8].CGColor; //圆点颜色；以色彩、饱和度、亮度和不透明度组合的颜色
     CGColorRef dotShadowColor = [UIColor orangeColor].CGColor; //圆点阴影颜色

     CGContextSetFillColorWithColor(context, dotColor); //设置填充色
     CGContextSetShadowWithColor(context, CGSizeMake(2.0, 2.0), , dotShadowColor); //设置阴影颜色；以阴影位置偏差为(2.0, 2.0)、模糊效果的 dotShadowColor 作为阴影颜色

     CGContextAddArc(context, 10.0, 10.0, 10.0, 0.0, radian(180.0), ); //添加圆点；以居中点为(10.0, 10.0)、半径为10.0、顺时针画0.0到180.0弧度的圆点（即为上半圆），注意0.0弧度为水平线左边位置开始
     CGContextFillPath(context);

     CGContextAddArc(context, 30.0, 20.0, 10.0, 0.0, radian(180.0), ); //添加圆点；以居中点为(30.0, 20.0)、半径为10.0、逆时针画0.0到180.0弧度的圆点（即为下半圆），注意0.0弧度为水平线左边位置开始
     CGContextFillPath(context);
 }

 /**
  *  绘画内容图层
  *
  *  @param layer   当前图层
  *  @param context 上下文
  */
 - (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context {
     //图层背景颜色
     CGColorRef backgroundColor = [UIColor lightGrayColor].CGColor;
     CGContextSetFillColorWithColor(context, backgroundColor);
     CGContextFillRect(context, layer.bounds);

     static const CGPatternCallbacks callbacks = { , &drawColoredPattern, NULL };
     //绘画连续的单元格，每个单元格的内容由 drawColoredPattern 方法决定
     CGContextSaveGState(context);
     CGColorSpaceRef patternSpace = CGColorSpaceCreatePattern(NULL);
     CGContextSetFillColorSpace(context, patternSpace);
     CGColorSpaceRelease(patternSpace);

     CGPatternRef pattern = CGPatternCreate(NULL,
                                            layer.bounds,
                                            CGAffineTransformIdentity,
                                            40.0, //单元格的宽度
                                            40.0, //单元格的高度
                                            kCGPatternTilingConstantSpacing,
                                            true,
                                            &callbacks);
     CGFloat alpha = 1.0; //着色模式内容的不透明度
     CGContextSetFillPattern(context, pattern, &alpha);
     CGPatternRelease(pattern);
     CGContextFillRect(context, layer.bounds);
     CGContextRestoreGState(context);
 }

 @end

ViewController.h

 //#import <UIKit/UIKit.h>
 #import <QuartzCore/CALayer.h>
 #import "KMLayerDelegate.h"

 @interface ViewController : UIViewController
 @property (strong, nonatomic) KMLayerDelegate *layerDelegate;

 @end

ViewController.m

 #import "ViewController.h"

 static CGFloat const kCornerRadius = 10.0;
 static CGFloat const kWidthOfIcon = 120.0;
 static CGFloat const kLineWidth = 5.0;
 static CGFloat const kBaseNumber = ; ///< 24等分法

 @interface ViewController ()
 - (void)createShadowCornerImage:(UIImage *)image withRootLayer:(CALayer *)rootLayer;
 - (void)createCustomDrawingLayer:(CALayer *)rootLayer;
 - (void)createSuccessIconDrawingLayer:(CALayer *)rootLayer;
 - (void)createWarningIconDrawingLayer:(CALayer *)rootLayer;
 - (void)createErrorIconDrawingLayer:(CALayer *)rootLayer;
 - (void)layoutUI;
 @end

 @implementation ViewController

 - (void)viewDidLoad {
     [super viewDidLoad];

     [self layoutUI];
 }

 - (void)didReceiveMemoryWarning {
     [super didReceiveMemoryWarning];
     // Dispose of any resources that can be recreated.
 }

 /**
  *  创建带阴影效果的圆角图片图层
  *
  *  @param image     图片
  *  @param rootLayer 根图层
  */
 - (void)createShadowCornerImage:(UIImage *)image withRootLayer:(CALayer *)rootLayer {
     // 子图层（图片的阴影图层）
     CALayer *subLayer = [CALayer layer];
     subLayer.frame = CGRectMake(20.0, 40.0, 150.0, 150.0);
     subLayer.backgroundColor = [UIColor lightGrayColor].CGColor;
     subLayer.cornerRadius = kCornerRadius;
     subLayer.borderColor = [UIColor blackColor].CGColor;
     subLayer.borderWidth = 2.0;
     subLayer.shadowColor = [UIColor blackColor].CGColor; // 设置阴影颜色
     subLayer.shadowOpacity = 0.7; // 设置阴影不透明度
     subLayer.shadowOffset = CGSizeMake(4.0, 3.0); // 设置阴影位置偏差
     subLayer.shadowRadius = 5.0; // 设置阴影圆角半径
     [rootLayer addSublayer:subLayer];

     // 子图层的子图层（图片的内容图层）
     CALayer *imageLayer = [CALayer layer];
     imageLayer.frame = subLayer.bounds;
     imageLayer.contents = (id)image.CGImage;
     imageLayer.masksToBounds = YES; // 设置标示剪切界限；内容图层需设置为 YES，才能有圆角效果
     imageLayer.cornerRadius = kCornerRadius;
     CGAffineTransform affineTransform = CGAffineTransformConcat(CGAffineTransformMakeScale(0.8, 0.8), CGAffineTransformMakeRotation(M_PI_4/)); // 合并缩放和旋转效果；以0.8比例居中缩放，以45度/9=5度的角度顺时针旋转
     imageLayer.affineTransform = affineTransform;
     [subLayer addSublayer:imageLayer];
 }

 /**
  *  创建自定义绘画内容图层（KMLayerDelegate）
  *
  *  @param rootLayer 根图层
  */
 - (void)createCustomDrawingLayer:(CALayer *)rootLayer {
     CALayer *drawingLayer = [CALayer layer];
     drawingLayer.frame = CGRectMake(200.0, 40.0, 150.0, 150.0);
     drawingLayer.backgroundColor = [UIColor orangeColor].CGColor; // 背景颜色会被内容图层遮住，所以最终呈现的以内容图层为准
     drawingLayer.masksToBounds = YES; // 设置标示剪切界限；内容图层需设置为 YES，才能有圆角效果
     drawingLayer.cornerRadius = kCornerRadius;
     drawingLayer.borderColor = [UIColor blackColor].CGColor;
     drawingLayer.borderWidth = 2.0;
     drawingLayer.shadowColor = [UIColor darkGrayColor].CGColor; // 设置阴影颜色
     drawingLayer.shadowOpacity = 0.8; // 设置阴影不透明度
     drawingLayer.shadowOffset = CGSizeMake(8.0, 6.0); // 设置阴影位置偏差
     drawingLayer.shadowRadius = 5.0; // 设置阴影圆角半径

     _layerDelegate = [KMLayerDelegate new];
     drawingLayer.delegate = _layerDelegate;
     [drawingLayer setNeedsDisplay]; // 这里必须调用方法 setNeedsDisplay，才会触发委托代理方法 drawLayer:
     [rootLayer addSublayer:drawingLayer];
 }

 /**
  *  创建绿色成功图标内容图层
  *
  *  @param rootLayer 根图层
  */
 - (void)createSuccessIconDrawingLayer:(CALayer *)rootLayer {
     // 成功图标颜色：绿色
     UIColor *const color = [UIColor colorWithRed:0.000 green:1.000 blue:0.502 alpha:1.000];

     // 贝塞尔曲线路径；开始画圆
     UIBezierPath* path = [UIBezierPath bezierPathWithOvalInRect: CGRectMake(0.0, 0.0, kWidthOfIcon, kWidthOfIcon)];
     // 然后以三点形成「打勾」效果
     [path moveToPoint:CGPointMake(kWidthOfIcon/kBaseNumber*, kWidthOfIcon/kBaseNumber*)];
     CGPoint p1 = CGPointMake(kWidthOfIcon/kBaseNumber*, kWidthOfIcon/kBaseNumber*);
     [path addLineToPoint:p1];

     CGPoint p2 = CGPointMake(kWidthOfIcon/kBaseNumber*, kWidthOfIcon/kBaseNumber*);
     [path addLineToPoint:p2];

     // 子图层
     CAShapeLayer *subLayer = [CAShapeLayer layer];
     subLayer.frame = CGRectMake(125.0, 210.0, kWidthOfIcon, kWidthOfIcon);
     subLayer.path = path.CGPath;
     subLayer.lineWidth = kLineWidth; // 线条宽度
     subLayer.strokeColor = color.CGColor; // 线条颜色
     subLayer.fillColor = [UIColor clearColor].CGColor; //清除填充色
     [rootLayer addSublayer:subLayer];
 }

 /**
  *  创建黄色警告图标内容图层
  *
  *  @param rootLayer 根图层
  */
 - (void)createWarningIconDrawingLayer:(CALayer *)rootLayer {
     CGFloat centerOfWidth = (kWidthOfIcon - kLineWidth)/;
     // 警告图标颜色：黄色
     UIColor *const color = [UIColor colorWithRed:1.000 green:0.800 blue:0.400 alpha:1.000];

     // 贝塞尔曲线路径；开始画圆
     UIBezierPath* path = [UIBezierPath bezierPathWithOvalInRect: CGRectMake(0.0, 0.0, kWidthOfIcon, kWidthOfIcon)];
     // 然后画感叹号
     [path moveToPoint:CGPointMake(centerOfWidth, kWidthOfIcon/kBaseNumber*)];
     CGPoint p1 = CGPointMake(centerOfWidth, kWidthOfIcon/kBaseNumber*);
     [path addLineToPoint:p1];

     [path moveToPoint:CGPointMake(centerOfWidth, kWidthOfIcon/kBaseNumber*)];
     [path addArcWithCenter:CGPointMake(centerOfWidth, kWidthOfIcon/kBaseNumber*) radius:3.0 startAngle: endAngle:M_PI* clockwise:YES];

     // 子图层
     CAShapeLayer *subLayer = [CAShapeLayer layer];
     subLayer.frame = CGRectMake(125.0, 360.0, kWidthOfIcon, kWidthOfIcon);
     subLayer.path = path.CGPath;
     subLayer.lineWidth = kLineWidth; // 线条宽度
     subLayer.strokeColor = color.CGColor; // 线条颜色
     subLayer.fillColor = [UIColor clearColor].CGColor; //清除填充色
     [rootLayer addSublayer:subLayer];
 }

 /**
  *  创建红色错误图标内容图层
  *
  *  @param rootLayer 根图层
  */
 - (void)createErrorIconDrawingLayer:(CALayer *)rootLayer {
     CGFloat keyVal1 = kWidthOfIcon/kBaseNumber*;
     CGFloat keyVal2 = kWidthOfIcon/kBaseNumber*;
     // 失败图标颜色：红色
     UIColor *const color = [UIColor colorWithRed:1.000 green:0.400 blue:0.400 alpha:1.000];

     // 贝塞尔曲线路径；开始画圆
     UIBezierPath* path = [UIBezierPath bezierPathWithOvalInRect: CGRectMake(0.0, 0.0, kWidthOfIcon, kWidthOfIcon)];
     // 然后画交叉号
     CGPoint p1 =  CGPointMake(keyVal1, keyVal1);
     [path moveToPoint:p1];

     CGPoint p2 =  CGPointMake(keyVal2, keyVal2);
     [path addLineToPoint:p2];

     CGPoint p3 =  CGPointMake(keyVal2, keyVal1);
     [path moveToPoint:p3];

     CGPoint p4 =  CGPointMake(keyVal1, keyVal2);
     [path addLineToPoint:p4];

     // 子图层
     CAShapeLayer *subLayer = [CAShapeLayer layer];
     subLayer.frame = CGRectMake(125.0, 510.0, kWidthOfIcon, kWidthOfIcon);
     subLayer.path = path.CGPath;
     subLayer.lineWidth = kLineWidth; // 线条宽度
     subLayer.strokeColor = color.CGColor; // 线条颜色
     subLayer.fillColor = [UIColor clearColor].CGColor; //清除填充色
     [rootLayer addSublayer:subLayer];
 }

 - (void)layoutUI {
     //根图层
     CALayer *rootLayer = self.view.layer;
     rootLayer.backgroundColor = [UIColor colorWithRed:0.769 green:0.940 blue:0.943 alpha:1.000].CGColor;
     rootLayer.cornerRadius = 40.0;

     [self createShadowCornerImage:[UIImage imageNamed:@"Emoticon_tusiji_icon2"]
                     withRootLayer:rootLayer];
     [self createCustomDrawingLayer:rootLayer];
     [self createSuccessIconDrawingLayer:rootLayer];
     [self createWarningIconDrawingLayer:rootLayer];
     [self createErrorIconDrawingLayer:rootLayer];
 }

 @end