前言借鑑標哥的部落格部分文章：http://www.henishuo.com/ios-cashapelayer-learning/

CAShapeLayer和drawRect的比較：

drawRect：屬於CoreGraphics框架，佔用CPU，效能消耗大，不建議重寫
CAShapeLayer：屬於CoreAnimation框架，通過GPU來渲染圖形，節省效能。動畫渲染直接提交給手機GPU，不消耗記憶體，這兩者各有各的用途，而不是說有了CAShapeLayer就不需要drawRect。

溫馨提示：drawRect只是一個方法而已，是UIView的方法，重寫此方法可以完成我們的繪製圖形功能。

CAShapeLayer與UIBezierPath的關係：

CAShapeLayer中shape代表形狀的意思，所以需要形狀才能生效
貝塞爾曲線可以建立基於向量的路徑，而UIBezierPath類是對CGPathRef的封裝
貝塞爾曲線給CAShapeLayer提供路徑，CAShapeLayer在提供的路徑中進行渲染。路徑會閉環，所以繪製出了Shape，用於CAShapeLayer的貝塞爾曲線作為path，其path是一個首尾相接的閉環的曲線，即使該貝塞爾曲線不是一個閉環的曲線

示例簡介：

在餅圖上顯示陣列中幾個資料各佔有的百分比，SliceLayer是CAShapeLayer的子類，用於構造餅圖的各個扇面和選中某扇面的動畫效果，PieChart是UIView的子類，用於根據陣列的資料情況來設定餅圖的各個扇面和觸控方法，最後在VC中呼叫即可。

示例程式碼：

#import <QuartzCore/QuartzCore.h>
#import <UIKit/UIKit.h>

@interface SliceLayer : CAShapeLayer

@property (nonatomic, assign) CGFloat startAngle;
@property (nonatomic, assign) CGFloat endAngle;
@property (nonatomic, assign) CGPoint centerPoint;
@property (nonatomic, assign) CGFloat radius;
@property (nonatomic, assign) BOOL selected;
@property (nonatomic, strong) NSString *text;
@property (nonatomic, assign) NSInteger tag;

- (void)create;

@end
 

#define RandomColor [UIColor colorWithRed:arc4random() % 255 / 255.0 green:arc4random() % 255 / 255.0 blue:arc4random() % 255 / 255.0 alpha:1.0]

#import "SliceLayer.h"

@implementation SliceLayer

- (void)create {
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:_centerPoint];
    [path addArcWithCenter:_centerPoint radius:_radius startAngle:_startAngle endAngle:_endAngle clockwise:YES];
    [path closePath];
    self.path = path.CGPath;
    self.strokeColor = [UIColor cyanColor].CGColor;
    self.fillColor = RandomColor.CGColor;
}

- (void)setSelected:(BOOL)selected {
    _selected = selected;
    CGPoint newCenterPoint = _centerPoint;
    if (selected) {
        newCenterPoint = CGPointMake(_centerPoint.x + cosf((_startAngle + _endAngle) / 2) * 30, _centerPoint.y + sinf((_startAngle + _endAngle) / 2) * 30);
    }
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:newCenterPoint];
    [path addArcWithCenter:newCenterPoint radius:_radius startAngle:_startAngle endAngle:_endAngle clockwise:YES];
    [path closePath];
    self.path = path.CGPath;
    
    CABasicAnimation *animation = [CABasicAnimation animation];
    animation.keyPath = @"path";
    animation.toValue = path;
    animation.duration = 0.5;
    [self addAnimation:animation forKey:nil];
}

@end
 

#import <UIKit/UIKit.h>
//typedef void(^MyBlock)(CGFloat);

@interface PieChart : UIView

@property (nonatomic, strong) NSArray *datas;
@property (nonatomic, strong) NSMutableArray *sliceLayerArray;
//@property (nonatomic, strong) MyBlock angleBlock;

@end

#import "PieChart.h"
#import "SliceLayer.h"

@implementation PieChart {
    CGFloat percentage;
}

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.sliceLayerArray = @[].mutableCopy;
    }
    return self;
}

- (void)setDatas:(NSArray *)datas {
    _datas = datas;
    CGFloat startAngle = 0;
    CGFloat endAngle = 0;
    for (int i = 0; i < datas.count; i++) {
        percentage = [datas[i] floatValue];
        CGFloat angle = percentage * M_PI * 2;
        endAngle = angle + startAngle;
        
        SliceLayer *sliceLayer = [[SliceLayer alloc] init];
        sliceLayer.startAngle = startAngle;
        sliceLayer.endAngle = endAngle;
        sliceLayer.radius = 100.0f;
        sliceLayer.centerPoint = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
        sliceLayer.tag = i;
        [sliceLayer create];
        [self.layer addSublayer:sliceLayer];
        [self.sliceLayerArray addObject:sliceLayer];
        
        CATextLayer *textLayer = [CATextLayer layer];
        textLayer.frame = CGRectMake(sliceLayer.centerPoint.x + cosf((startAngle + endAngle) / 2) * 50 - 15, sliceLayer.centerPoint.y + sinf((startAngle + endAngle) / 2) * 50 - 10, 40, 20);
        textLayer.string = [NSString stringWithFormat:@"%1.f%%", percentage * 100];
        textLayer.fontSize = 17;
        textLayer.contentsScale = 2;
        
        [sliceLayer addSublayer:textLayer];
        
        startAngle = endAngle;
        
    }
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    CGPoint touchPoint = [[touches anyObject] locationInView:self];
    for (SliceLayer *slice in _sliceLayerArray) {
        //判斷選擇區域
        if (CGPathContainsPoint(slice.path, 0, touchPoint, YES)) {
            slice.selected = YES;
//            self.angleBlock((slice.endAngle - slice.startAngle) / 2 / M_PI);
        } else {
            slice.selected = NO;
        }
    }
}

#import "ViewController.h"
#import "PieChart.h"
@class PieChart;

@interface ViewController () {
    CAShapeLayer *shapeLayer;
    NSTimer *timer;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor blackColor];
    
    PieChart *pieChart = [[PieChart alloc] initWithFrame:self.view.bounds];
    pieChart.datas = @[@0.1, @0.2, @0.3, @0.25, @0.1, @0.05];
    pieChart.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:pieChart];
}