#import <Foundation/Foundation.h>

@interface NPArrowImageManager : NSObject


/**
 返回一張尖角圖片，尖角朝左
 
 @param image 圖片
 @param imageSize 尖角圖片大小
 @return 尖角朝左的圖片
 */
+ (UIImage *)arrowLeftImage:(UIImage *)image size:(CGSize)imageSize;

/**
 返回一張尖角圖片，尖角朝右

 @param image 圖片
 @param imageSize 尖角圖片大小
 @return 尖角朝右的圖片
 */
+ (UIImage *)arrowRightImage:(UIImage *)image size:(CGSize)imageSize;


@end

#import "NPArrowImageManager.h"

#define kArrowWidth 6       // 尖角寬度
#define kArrowMarginTop 13  // 尖角距離頂部距離
#define kArrowHeight 10     // 尖角高度

@implementation NPArrowImageManager

/**
 返回一張尖角圖片，尖角朝左
 
 @param image 圖片
 @param imageSize 尖角圖片大小
 @return 尖角朝左的圖片
 */
+ (UIImage *)arrowLeftImage:(UIImage *)image size:(CGSize)imageSize
{
    // 1.創建圖片上下文
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);
    // 2.獲取圖片上下文
    CGContextRef contentRef = UIGraphicsGetCurrentContext();
    
    // 3.創建路徑
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(kArrowWidth, 0, imageSize.width-kArrowWidth, imageSize.height) cornerRadius:6];
    [path moveToPoint:CGPointMake(kArrowWidth, 0)];
    [path addLineToPoint:CGPointMake(kArrowWidth, kArrowMarginTop)];
    [path addLineToPoint:CGPointMake(0, kArrowMarginTop + 0.5*kArrowHeight)];
    [path addLineToPoint:CGPointMake(kArrowWidth, kArrowMarginTop+kArrowHeight)];
    [path closePath];
    
    // 4.把路徑添加到上下文中
    CGContextAddPath(contentRef, path.CGPath);
    
    // 5.裁剪上下文
    CGContextEOClip(contentRef);
    
    // 6.把圖片畫到上下文中
    [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    
    // 7.從上下文中取出圖片
    UIImage *arrowImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 8.結束圖片上下文
    UIGraphicsEndImageContext();
    
    return arrowImage;
}

/**
 返回一張尖角圖片，尖角朝右
 
 @param image 圖片
 @param imageSize 尖角圖片大小
 @return 尖角朝右的圖片
 */
+ (UIImage *)arrowRightImage:(UIImage *)image size:(CGSize)imageSize
{
    // 1.創建圖片上下文
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);
    // 2.獲取圖片上下文
    CGContextRef contentRef = UIGraphicsGetCurrentContext();
    
    // 3.創建路徑
    CGFloat imageW = imageSize.width;
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, imageSize.width - kArrowWidth, imageSize.height) cornerRadius:6];
    [path moveToPoint:CGPointMake(imageW - kArrowWidth, 0)];
    [path addLineToPoint:CGPointMake(imageW - kArrowWidth, kArrowMarginTop)];
    [path addLineToPoint:CGPointMake(imageW, kArrowMarginTop + 0.5 * kArrowHeight)];
    [path addLineToPoint:CGPointMake(imageW - kArrowWidth, kArrowMarginTop + kArrowHeight)];
    [path closePath];
    
    // 4.把路徑添加到上下文中
    CGContextAddPath(contentRef, path.CGPath);
    
    // 5.裁剪上下文
    CGContextEOClip(contentRef);
    
    // 6.把圖片畫到上下文中
    [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    
    // 7.從上下文中取出圖片
    UIImage *arrowImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 8.結束圖片上下文
    UIGraphicsEndImageContext();
    
    return arrowImage;
}


@end

使用示例：

#import "ViewController.h"
#import "NPArrowImageTool.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    [self setupUI];
}

- (void)setupUI {
    UIImage *image = [UIImage imageNamed:@"ball"];

    // 左尖角
    UIImageView *leftImageView = [[UIImageView alloc] initWithFrame:CGRectMake(20, 100, 90, 160)];
    leftImageView.image = [NPArrowImageTool arrowLeftImage:image size:leftImageView.bounds.size];
    [self.view addSubview:leftImageView];

    // 右尖角
    UIImage *arrowRightImage = [NPArrowImageTool arrowRightImage:image size:CGSizeMake(90, 160)];
    UIImageView *rightImageView = [[UIImageView alloc] initWithImage:arrowRightImage];
    rightImageView.frame = CGRectOffset(leftImageView.frame, 130, 0);
    [self.view addSubview:rightImageView];
}

@end