详解：IOS二维码的生成与扫描过程

 // 二维码的生成
 // 1、创建过滤器
 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
 self.imageView.image = [UIImage imageWithCIImage:outputImage];

/**
 * 根据CIImage生成指定大小的UIImage
 *
 * @param image CIImage
 * @param size 图片宽度
 */
- (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];
}

NSString *str = @http://www.baidu.com;

#import "ViewController.h"
#import 
@interface ViewController () 
/**显示图层*/
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *layer;
/**捕捉会话*/
@property (nonatomic, strong) AVCaptureSession *session;
@end
@implementation ViewController

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
 // 二维码的扫描
 // 1、创建捕捉会话
 AVCaptureSession *session = [[AVCaptureSession alloc] init];
 self.session = session;
 // 2.添加输入设备(数据从摄像头输入)
 AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
 AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:nil];
 [session addInput:input];
 // 3、添加输出数据(示例对象-->类对象-->元类对象-->根元类对象)
 AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
 [output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
 [session addOutput:output];
 // 3.1.设置输入元数据的类型(类型是二维码数据)
 [output setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
 // 4、添加扫描图层
 AVCaptureVideoPreviewLayer *layer = [AVCaptureVideoPreviewLayer layerWithSession:session];
 layer.frame = self.view.bounds;
 [self.view.layer addSublayer:layer];
 self.layer = layer;
 // 5、开始扫描
 [session startRunning];
}
/**
 * 实现output的回调方法
 */
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
 // 数组metadataObjects中存放结果数据
 if (metadataObjects.count > 0) {
 // 获取最终的读取结果
 AVMetadataMachineReadableCodeObject *object = [metadataObjects lastObject];
 NSLog(@"%@",object.stringValue);
 [self.session stopRunning];
 [self.layer removeFromSuperlayer];
 }
 else
 {
 NSLog(@"没有扫描到数据");
 }
}