二维码

初次接触二维码扫描的时候还是iOS4.3的系统，那时候还没有原生的API，记得当时是使用zbar来弄的，那个麻烦啊……现在好了，Core Image就可以实现二维码的生成和从图片识别二维码。

一、二维码的生成

使用CIQRCodeGenerator滤镜即可从字符串生成二维码：

+ (UIImage *)generateQRCode:(NSString *)inputMessage size:(CGSize)size {
    
    NSData *data = [inputMessage dataUsingEncoding:NSISOLatin1StringEncoding allowLossyConversion:NO];
    
    //inputCorrectionLevel 二维码的容错率 L: 7% M: 15% Q: 25% H: 30%
    CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"
                            withInputParameters:@{@"inputMessage": data, @"inputCorrectionLevel" : @"Q"}];
    
    CIImage *image = [filter outputImage];
    
    CIContext *context = [CIContext contextWithOptions:nil];
    //改变尺寸前的位图
    CGImageRef bitmap = [context createCGImage:image fromRect:image.extent];
    
    CGFloat sx = size.width / image.extent.size.width;
    CGFloat sy = size.height / image.extent.size.height;
    
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceGray();
    //位图上下文
    CGContextRef bitmapRef = CGBitmapContextCreate(nil, size.width, size.height, 8, 0, colorSpaceRef, 0);
    CGContextSetInterpolationQuality(bitmapRef, kCGInterpolationNone);
    CGContextScaleCTM(bitmapRef, sx, sy);
    
    //重画图片
    CGContextDrawImage(bitmapRef, image.extent, bitmap);
    
    CGImageRef scaleImage = CGBitmapContextCreateImage(bitmapRef);
    
    return [[UIImage alloc] initWithCGImage:scaleImage];
}

CIQRCodeGenerator生成的二维码图片大小是不固定的，所以需要重画缩放图片到指定大小。

二、从图片检测二维码

使用CIDetector来实现：

+ (NSString *)detecteQRCode:(UIImage *)image {
    
    CIContext *context = [CIContext contextWithOptions:nil];
    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeQRCode context:context options:@{CIDetectorAccuracy:CIDetectorAccuracyHigh}];
    NSArray *features = [detector featuresInImage:[CIImage imageWithCGImage:image.CGImage]];
    if (features && features.count > 0) {
        
        return ((CIQRCodeFeature *)features[0]).messageString;
    }
    
    return nil;
}

三、扫描二维码

可使用AVFoundation来扫描二维码：

在ViewController中增加以下定义：

@property (nonatomic, strong) UIView *viewPreview;
@property (nonatomic, strong) AVCaptureSession *captureSession;
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *videoPreviewLayer;

关键代码：

- (BOOL)startScanning {
    
    NSError *error;
    
    AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
    if (!input) {
        NSLog(@"%@", [error localizedDescription]);
        return NO;
    }
    
    _captureSession = [[AVCaptureSession alloc] init];
    [_captureSession addInput:input];
    
    AVCaptureMetadataOutput *captureMetadataOutput = [[AVCaptureMetadataOutput alloc] init];
    [_captureSession addOutput:captureMetadataOutput];
    
    dispatch_queue_t dispatchQueue;
    dispatchQueue = dispatch_queue_create("captureQueue", NULL);
    [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
    [captureMetadataOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
    
    _videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
    [_videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
    [_videoPreviewLayer setFrame:_viewPreview.layer.bounds];
    [_viewPreview.layer addSublayer:_videoPreviewLayer];
    
    [_captureSession startRunning];
    
    return YES;
}

声明和实现AVCaptureMetadataOutputObjectsDelegate协议

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
    
    if (metadataObjects != nil && [metadataObjects count] > 0) {
        AVMetadataMachineReadableCodeObject *metadataObj = [metadataObjects objectAtIndex:0];
        if ([[metadataObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
            NSLog(@"Code: %@", [metadataObj stringValue]);
        }
    }
}

以上代码会在设备扫描到二维码后将字符串输出到控制台。