为什么我用ios7 系统的AVFoundation 不能扫描条形码，只能扫描二维码

//
// ViewController.m
// 条形码三
//
// Created by mac on 15/6/17.
// Copyright (c) 2015年 郑氏集团. All rights reserved.
//

#import "ViewController.h"
#import

@interface ViewController ()
@property (nonatomic, strong) AVCaptureSession *captureSession;
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *videoPreviewLayer;
@property (weak, nonatomic) IBOutlet UIView *viewPreview;
@property (weak, nonatomic) IBOutlet UILabel *lblStatus;
@property (weak, nonatomic) IBOutlet UIButton *bbitemStart;
@property (nonatomic) BOOL isReading;
@property (nonatomic, strong) AVAudioPlayer *audioPlayer;
@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];
  _isReading = NO;

  _captureSession = nil;
  [self loadBeepSound];
  // Do any additional setup after loading the view, typically from a nib.
  }

• (IBAction)startStopReading:(id)sender {
  if (!_isReading) {
  if ([self stopReading]) {
  // [_bbitemStart setTitle:@"Stop"];
  [_lblStatus setText:@"Scanning for QR Code..."];
  }
  }
  else{
  [self startReading];
  // [_bbitemStart setTitle:@"Start!"];
  }

  _isReading = !_isReading;
  }

• (BOOL)startReading {
  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("myQueue", NULL);
  [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
  captureMetadataOutput.metadataObjectTypes=@[ AVMetadataObjectTypeQRCode,AVMetadataObjectTypeCode39Code,AVMetadataObjectTypeCode128Code,AVMetadataObjectTypeCode39Mod43Code,AVMetadataObjectTypeEAN13Code,AVMetadataObjectTypeEAN8Code,AVMetadataObjectTypeCode93Code];

  _videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
  [_videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
  [_videoPreviewLayer setFrame:_viewPreview.layer.bounds];
  [_viewPreview.layer addSublayer:_videoPreviewLayer];

  [_captureSession startRunning];

  return YES;
  }
  -(BOOL)stopReading{
  [_captureSession stopRunning];
  _captureSession = nil;

  [_videoPreviewLayer removeFromSuperlayer];
  return YES;
  }
  -(void)loadBeepSound{
  NSString *beepFilePath = [[NSBundle mainBundle] pathForResource:@"beep" ofType:@"mp3"];
  NSURL *beepURL = [NSURL URLWithString:beepFilePath];
  NSError *error;

  _audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:beepURL error:&error];
  if (error) {
  NSLog(@"Could not play beep file.");
  NSLog(@"%@", [error localizedDescription]);
  }
  else{
  [_audioPlayer prepareToPlay];
  }
  }

-(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]) {
[_lblStatus performSelectorOnMainThread:@selector(setText:) withObject:[metadataObj stringValue] waitUntilDone:NO];

        [self performSelectorOnMainThread:@selector(stopReading) withObject:nil waitUntilDone:NO];
        [_bbitemStart performSelectorOnMainThread:@selector(setTitle:) withObject:@"Start!" waitUntilDone:NO];
        _isReading = NO;
        if (_audioPlayer) {
            [_audioPlayer play];
    }
}

}

}

• (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. }

@end

我也遇到这个问题，解决了吗？