为什么带有MTBBarcodeScanner的iPad上的相机无法正常工作？

Question

我编写了一个简单的UIViewController ，它使用MTBBarcodeScanner扫描条形码。 无论是Xcode的开发版本还是diawi.com的AdHoc发行版，它都能在运行iOS 10的iPhone 6s +上完美运行。 不幸的是，通过Xcode或AdHoc分发时，它不能在iPad（也运行iOS 10）上运行。 我的视图控制器正确滑动，按钮按预期工作，但预览窗口显示无视频，也没有条形码被读取。

在加载此视图控制器之前，我已经检查了用户的权限。 我从iOS获得了弹出窗口，并在两个平台上都将其授予了权限。 iPad的“设置”应用程序显示我确实有权使用相机。

这是我的代码。

#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

感谢Mike Buss为我提供帮助。 他告诉我，我可能开相机太早。 他建议我将startScanningWithResultBlock:调用移至viewDidAppear:animated 。 我用iPad进行了测试，现在效果很好。