二维码生成（利用iOS CoreImage框架）

//
//  ViewController.m

#import "ViewController.h"
#import <CoreImage/CoreImage.h> //导入框架

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIImageView *qrcodeView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
    // 2、恢复滤镜的默认属性
    [filter setDefaults];
    // 3、设置内容
    NSString *str = @"这是一个二维码的生成结果";
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
    // 使用KVO设置属性
    [filter setValue:data forKey:@"inputMessage"];
    // 4、获取输出文件
    CIImage *outputImage = [filter outputImage];
    // 5、显示二维码
    UIImage *image =[self createNonInterpolatedUIImageFormCIImage:outputImage withSize:500.0f];
    self.qrcodeView.image =image;

}
- (UIImage *)createNonInterpolatedUIImageFormCIImage:(CIImage *)image withSize:(CGFloat) size
{
    CGRect extent = CGRectIntegral(image.extent);
    CGFloat scale = MIN(size/CGRectGetWidth(extent), size/CGRectGetHeight(extent));
    // 1.创建bitmap;
    size_t width = CGRectGetWidth(extent) * scale;
    size_t height = CGRectGetHeight(extent) * scale;
    CGColorSpaceRef cs = CGColorSpaceCreateDeviceGray();
    CGContextRef bitmapRef = CGBitmapContextCreate(nil, width, height, 8, 0, cs, (CGBitmapInfo)kCGImageAlphaNone);
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef bitmapImage = [context createCGImage:image fromRect:extent];
    CGContextSetInterpolationQuality(bitmapRef, kCGInterpolationNone);
    CGContextScaleCTM(bitmapRef, scale, scale);
    CGContextDrawImage(bitmapRef, extent, bitmapImage);
    // 2.保存bitmap到图片
    CGImageRef scaledImage = CGBitmapContextCreateImage(bitmapRef);
    CGContextRelease(bitmapRef);
    CGImageRelease(bitmapImage);
    return [UIImage imageWithCGImage:scaledImage];
}
@end