AVCaptureSession output is not properly displayed and AVCaptureMetadataOutputObjectsDelegate method is not called - ios

Question

I have a single view application in which I am trying to test iOS7's AVCaptureMetadataOutput based on this explanation. My ViewController conforms to AVCaptureMetadataOutputObjectsDelegate and the code looks like this (almost exactly the same as Mattt's):
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
// Testing the VIN Scanner before I make it part of the library
NSLog(#"Setting up the vin scanner");
AVCaptureSession *session = [[AVCaptureSession alloc] init];
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
error:&error];
if (input) {
[session addInput:input];
} else {
NSLog(#"Error: %#", error);
}
AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[session addOutput:output];
[session startRunning];
}
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputMetadataObjects:(NSArray *)metadataObjects
fromConnection:(AVCaptureConnection *)connection
{
NSString *code = nil;
for (AVMetadataObject *metadata in metadataObjects) {
if ([metadata.type isEqualToString:AVMetadataObjectTypeCode39Code]) {
code = [(AVMetadataMachineReadableCodeObject *)metadata stringValue];
break;
}
}
NSLog(#"code: %#", code);
}
When I run this on an iOS7 device (I've tried an iPhone 4 and iPhone 4s) XCode logs "Setting up the vin scanner" but the camera (ie the AVCaptureSession) never opens.
Edit 1:
I added the following code to show the camera output on screen:
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
// Display full screen
previewLayer.frame = self.view.frame;
// Add the video preview layer to the view
[self.view.layer addSublayer:previewLayer];
But the display is very odd, does not conform to the screen and the way it rotates does not make sense. The other issue is that when I focus the camera on a bar code the metadata delegate method is never called. Please see pictures below:

Answer 1

The camera will not open the way it does for the UIImagePickerController. The problem is that your code does nothing with the output. You'll need to add a preview layer to display the output of the camera as it streams in.
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
// Display full screen
previewLayer.frame = CGRectMake(0.0, 0.0, self.view.frame.size.width, self.view.frame.size.height);
// Add the video preview layer to the view
[self.view.layer addSublayer:previewLayer];
[session startRunning];
Edit**
After taking a deeper look at your code I noticed a few more issues.
First you need to also set the MetaDataObjectTypes you want to search for, right now your not looking for any valid object types. This should be added after you add the output to the session. You can view the full list of available types in the documentation
[output setMetadataObjectTypes:#[AVMetadataObjectTypeQRCode, AVMetadataObjectTypeEAN13Code]];
Second your AVCaptureSession *session is a local variable in your viewDidLoad, take this and place it just after your #interface ViewController () as shown below.
#interface ViewController ()
#property (nonatomic, strong) AVCaptureSession *session;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.session = [[AVCaptureSession alloc] init];
// Testing the VIN Scanner before I make it part of the library
NSLog(#"Setting up the vin scanner");
self.session = [[AVCaptureSession alloc] init];
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
error:&error];
if (input) {
[self.session addInput:input];
} else {
NSLog(#"Error: %#", error);
}
AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[self.session addOutput:output];
[output setMetadataObjectTypes:#[AVMetadataObjectTypeQRCode, AVMetadataObjectTypeEAN13Code]];
[self.session startRunning];
}