提高读取UPC-A条码Objective-C（Xcode）的速度

Question

我正在尝试加快我的应用程序中条形码的读取速度，该应用程序可以正常工作，但在读取条形码时有点慢。

如何提高读取条形码的速度？

这里是我到目前为止的代码。

#import "ScanViewController.h"
#import "Utils.h"
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioToolbox.h>

@interface ScanViewController ()<AVCaptureMetadataOutputObjectsDelegate>

@property (nonatomic, readwrite) AVCaptureSession *captureSession;
@property (nonatomic, readwrite) AVCaptureVideoPreviewLayer *videoPreviewLayer;
@property (nonatomic, readwrite) UIView *qrCodeFrameView;
@property (nonatomic, readwrite) UILabel *qrCodeTextView;
@property (nonatomic, readwrite) NSArray *supportedCodeTypes;
@property (nonatomic, readwrite) long long lastScanTime;
@property (nonatomic, readwrite) NSString *lastScanCode;
@property (nonatomic, readwrite) AVAudioPlayer *audioPlayer;

@end

@implementation ScanViewController



- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.


    self.captureSession = [AVCaptureSession new];

    self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;
    self.supportedCodeTypes = @[AVMetadataObjectTypeUPCECode,
                                AVMetadataObjectTypeEAN13Code,
                                AVMetadataObjectTypeEAN8Code];
//                               AVMetadataObjectTypeCode39Code,
//                               AVMetadataObjectTypeCode39Mod43Code,
//                               AVMetadataObjectTypeCode93Code,
//                               AVMetadataObjectTypeCode128Code,
//                               AVMetadataObjectTypeAztecCode,
//                               AVMetadataObjectTypePDF417Code,
//                               AVMetadataObjectTypeITF14Code,
//                               AVMetadataObjectTypeDataMatrixCode,
//                               AVMetadataObjectTypeInterleaved2of5Code,
//                               AVMetadataObjectTypeQRCode];


    AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVCaptureSessionPre];
    if(captureDevice == nil) {
        NSLog(@"Failed to get the camera device");
        return;
    }

    @try {
        // Get an instance of the AVCaptureDeviceInput class using the previous device object.
        AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:nil];

        // Set the input device on the capture session.
        [self.captureSession addInput:input];

        // Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
        AVCaptureMetadataOutput *captureMetadataOutput = [[AVCaptureMetadataOutput alloc] init];
        [self.captureSession addOutput:captureMetadataOutput];

        // Set delegate and use the default dispatch queue to execute the call back
        [captureMetadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
        captureMetadataOutput.metadataObjectTypes = self.supportedCodeTypes;
        //            captureMetadataOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.qr]
    } @catch (NSException *error) {
        // If any error occurs, simply print it out and don't continue any more.
        NSLog(@"%@", error);
        return;
    }

    // Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
    self.videoPreviewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];
    self.videoPreviewLayer.videoGravity = kCAGravityResizeAspectFill;
    self.videoPreviewLayer.frame = self.view.layer.bounds;
    [self.view.layer addSublayer:self.videoPreviewLayer];

    // Start video capture.
    [self.captureSession startRunning];

    // Move the result view and loading view to the front
    [self.view bringSubviewToFront:self.resultView];
    [self.view bringSubviewToFront:self.loadingView];

    // Initialize QR Code Frame to highlight the QR code
    self.qrCodeFrameView = [[UIView alloc] init];
    if (self.qrCodeFrameView) {
        self.qrCodeFrameView.layer.borderColor = UIColor.greenColor.CGColor;
        self.qrCodeFrameView.layer.borderWidth = 2;
        [self.view addSubview:self.qrCodeFrameView];
        [self.view bringSubviewToFront:self.qrCodeFrameView];
    }

    self.qrCodeTextView = [[UILabel alloc] init];
    if (self.qrCodeTextView) {
        [self.qrCodeTextView setTextColor:UIColor.greenColor];
        [self.qrCodeTextView setFont:[UIFont systemFontOfSize:20]];
        [self.qrCodeFrameView addSubview:self.qrCodeTextView];
    }

    [self rotateLoadingImage];
    [self setResultType:RESULT_TYPE_WORKING codeContent:@"Ready" price:0.00];
    [self.loadingView setHidden:YES];

}

-(void)viewWillDisappear:(BOOL)animated {
    if (self.audioPlayer != nil) {
        [self.audioPlayer stop];
        self.audioPlayer = nil;
    }

    [super viewWillDisappear:animated];
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/
-(void) updatePreviewLayer:(AVCaptureConnection*)layer orientation:(AVCaptureVideoOrientation)orientation {
    layer.videoOrientation = orientation;
    self.videoPreviewLayer.frame = self.view.bounds;
}

-(void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    if(self.videoPreviewLayer.connection != nil) {
        UIDevice *currentDevice = [UIDevice currentDevice];
        UIDeviceOrientation orientation = [currentDevice orientation];
        AVCaptureConnection *previewLayerConnection = self.videoPreviewLayer.connection;

        if(previewLayerConnection.isVideoOrientationSupported) {
            switch (orientation) {
                case UIDeviceOrientationPortrait:
                    [self updatePreviewLayer:previewLayerConnection orientation:AVCaptureVideoOrientationPortrait];
                    break;
                case UIDeviceOrientationLandscapeRight:
                    [self updatePreviewLayer:previewLayerConnection orientation:AVCaptureVideoOrientationLandscapeLeft];
                    break;
                case UIDeviceOrientationLandscapeLeft:
                    [self updatePreviewLayer:previewLayerConnection orientation:AVCaptureVideoOrientationLandscapeRight];
                    break;
                case UIDeviceOrientationPortraitUpsideDown:
                    [self updatePreviewLayer:previewLayerConnection orientation:AVCaptureVideoOrientationPortraitUpsideDown];
                    break;
                default:
                    [self updatePreviewLayer:previewLayerConnection orientation:AVCaptureVideoOrientationPortrait];
                    break;
            }
        }
    }
}

-(void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
    // Check if the metadataObjects array is not nil and it contains at least one object.
    if (metadataObjects.count == 0) {
        self.qrCodeFrameView.frame = CGRectZero;
        return;
    }

    // Get the metadata object.
    AVMetadataMachineReadableCodeObject *metadataObj = (AVMetadataMachineReadableCodeObject*)(metadataObjects[0]);

    if ([self.supportedCodeTypes containsObject:metadataObj.type]) {
        // If the found metadata is equal to the QR code metadata (or barcode) then update the status label's text and set the bounds
        AVMetadataObject *barCodeObject = [self.videoPreviewLayer transformedMetadataObjectForMetadataObject:metadataObj];
        NSString *code = metadataObj.stringValue;

        if (code != nil) {
            // check upc a code
            if ([self checkUpcACode:metadataObj.type code:code] == NO) {
                self.qrCodeTextView.text = @"";
                return;
            }

            int i=0;
            for (i=0; i<code.length; i++) {
                char ch = [code characterAtIndex:i];
                if (ch != '0') break;
            }
            if (i>0) i--;
            code = [code substringFromIndex:i];

            self.qrCodeFrameView.frame = barCodeObject.bounds;
            [self.qrCodeTextView setText:code];
            self.qrCodeTextView.frame = CGRectMake(0, self.qrCodeFrameView.frame.size.height-20, self.qrCodeFrameView.frame.size.width, 20);
            NSLog(@"%@", code);

            [self handleBarcode:code];
        } else {
            self.qrCodeTextView.text = @"";
        }
    }
}

-(BOOL)checkUpcACode:(AVMetadataObjectType)type code:(NSString*)code {
    if (type == AVMetadataObjectTypeEAN13Code) {
        if ([code hasPrefix:@"0"] && [code length] > 0) {
            return YES;
        }
    }
    return NO;
}



@end```