Why isn't the camera working on my iPad with MTBBarcodeScanner? - ios

Question

I've written a simple UIViewController that uses MTBBarcodeScanner to scan barcodes. It works perfectly on my iPhone 6s+ running iOS 10, no matter if it's a development build from Xcode or an AdHoc distribution from diawi.com. Unfortunately, it's not working on iPad (also running iOS 10), when distributed through Xcode or the AdHoc thing. My view controller slides in correctly, the buttons work as expected, but the preview window shows no video and no barcodes ever get read.
Before this view controller loads, I've already checked for permission with the user. I got the popup from iOS and granted it on both platforms. The Settings app for the iPad shows that I indeed have access to the camera.
Here's my code.
#import "BarCodeScannerViewController.h"
#import <AudioToolbox/AudioToolbox.h>
#import <AVFoundation/AVFoundation.h>
#import <MTBBarcodeScanner/MTBBarcodeScanner.h>
#interface BarCodeScannerViewController ()
#property (nonatomic, strong) MTBBarcodeScanner *scanner;
#end
#implementation BarCodeScannerViewController
- (void) loadView; {
[super loadView];
[self setTitle:#"Scan Bar Code"];
UIView *preview = [[UIView alloc] init];
[[self view] addSubview:preview];
[preview setTranslatesAutoresizingMaskIntoConstraints:NO];
[self setScanner:[[MTBBarcodeScanner alloc] initWithMetadataObjectTypes:#[AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeQRCode] previewView:preview]];
UIView *buttonBar = [[UIView alloc] init];
[[self view] addSubview:buttonBar];
[buttonBar setTranslatesAutoresizingMaskIntoConstraints:NO];
[buttonBar setBackgroundColor:[UIColor colorWithWhite:0 alpha:.5]];
UIButton *cancelButton = [[UIButton alloc] init];
[buttonBar addSubview:cancelButton];
[cancelButton setTranslatesAutoresizingMaskIntoConstraints:NO];
[cancelButton addTarget:self action:#selector(cancel) forControlEvents:UIControlEventTouchUpInside];
[cancelButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[cancelButton setTitle:#"Cancel" forState:UIControlStateNormal];
UIButton *torchToggle = nil;
if ([[self scanner] hasTorch]) {
UIButton *torchToggle = [[UIButton alloc] init];
[buttonBar addSubview:torchToggle];
[torchToggle setTranslatesAutoresizingMaskIntoConstraints:NO];
[torchToggle addTarget:[self scanner] action:#selector(toggleTorch) forControlEvents:UIControlEventTouchUpInside];
[torchToggle setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[torchToggle setTitle:#"Toggle Light" forState:UIControlStateNormal];
}
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:preview attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeTop multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:preview attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:preview attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeRight multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:preview attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:buttonBar attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual
toItem:nil attribute:NSLayoutAttributeHeight multiplier:1.0 constant:44.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:buttonBar attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:buttonBar attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeRight multiplier:1.0 constant:0.0]];
[[self view] addConstraint:[NSLayoutConstraint constraintWithItem:buttonBar attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual
toItem:[self view] attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0]];
[buttonBar addConstraint:[NSLayoutConstraint constraintWithItem:cancelButton attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual
toItem:buttonBar attribute:NSLayoutAttributeLeft multiplier:1.0 constant:5.0]];
[buttonBar addConstraint:[NSLayoutConstraint constraintWithItem:cancelButton attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual
toItem:buttonBar attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-5.0]];
if ([[self scanner] hasTorch]) {
[buttonBar addConstraint:[NSLayoutConstraint constraintWithItem:torchToggle attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual
toItem:buttonBar attribute:NSLayoutAttributeRight multiplier:1.0 constant:-5.0]];
[buttonBar addConstraint:[NSLayoutConstraint constraintWithItem:torchToggle attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual
toItem:buttonBar attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-5.0]];
}
[_scanner startScanningWithResultBlock:^(NSArray *codes) {
for (AVMetadataMachineReadableCodeObject *code in codes) {
if ([code stringValue]) {
[_scanner stopScanning];
AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
if ([self barCodeScanned]) [self barCodeScanned]([code stringValue], self);
break;
}
}
} error:nil];
}
- (void) cancel;
{
[[self scanner] stopScanning];
[self dismissViewControllerAnimated:YES completion:nil];
}
#end

Answer 1

Thanks to Mike Buss for assisting me with this. He told me that I was probably starting the camera too early. He suggested I move the startScanningWithResultBlock: call to viewDidAppear:animated. I tested it with my iPad and it's working great now.