Reading Barcodes on iOS 7

iOS 7 introduced APIs to read bar codes using the camera. I could have easily overlooked it without this excellent post from doubleencore.

NSHipster provided sample code, but it missed some details to work. Here is a sample which does.

Sample code

Pitfalls

The issue I had with NSHipster’s sample code is the delegate method was not called at all. I quickly understood this was because the AVCaptureMetadataOutput must be configured to tell which metadata to recognise.

But, and this was not obvious to me, -[AVCaptureMetadataOuput setMetadataObjectTypes:] must be called after -[AVCaptureSession addOutput:]. Otherwise, the following message shows in the console:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[AVCaptureMetadataOutput setMetadataObjectTypes:] - unsupported type found.  Use -availableMetadataObjectTypes.'

I did try to look at the output of -availableMetadataObjectTypes, and it returns an empty array.

Therefore, -addOuput: must be called before setMetadataObjectTypes. In retrospect, it makes sense: the output object must know it is linked to a video session to know which metadata it may provide.