Help required in integrating Objective-C code in Qt6

[TheCrowKaka]

Hello

My environment is Qt6.4 on Iphone. I am looking at interfacing this simple Barcode Scanner code written in Objective C Using AVFoundation.h for a simple QtWidgets application.

This is the link to the Objective-C Code.
https://gist.github.com/Alex04/6976945

I successfully ran this code using XCode on an Iphone... It works really good.

Somehow, I am unable to understand the right way to interface this program with Qt6.

What I want to do is when I press a Pushbutton, This code is called which displays the camera for scanning the barcode. Then if the barcode is scanned the data is returned to the Qt Code which i can display in a Label.

Usually, I like to try a few things before asking for help. So I opened a new project and included all the files in the project. I have used simple routine to read the Mac Address of the Iphone but this looks quite a big code in Objective C an somehow all the information that I could go through, I could not understand the steps to integrate this code with Qt.

Can someone please help?

Thanks in advance.

[SGaist]

Hi,

Since you want to integrate that code into a C++ project, you need to go from Objective-C to Objective-C++.

The header you will use into your C++ application must be plain C++. Hence you should use something like the PIMPL idiom in order to "hide" the pure Objective-C part.

[TheCrowKaka]

@SGaist Thanks for the suggestion.

The original Code that I want to integrate is actually on this link.
https://github.com/renatosc/qrbarcodescanner-simple

I am also taking help of this post... not so successfully
https://stackoverflow.com/questions/1061005/calling-objective-c-method-from-c-member-function

In this post, there are two different methods suggested. One is not based on the PIMPL idiom whereas other is based on the PIMPL idiom.
Somehow, I have too many questions regarding implementation of the PIMPL idiom type of method. Hence I decided to try the other one.
This is what I have done so far.

This is the ScannerViewController.h file that I have created.

#ifndef SCANNERVIEWCONTROLLER_H
#define SCANNERVIEWCONTROLLER_H

void ScannerViewController(void);

#endif // SCANNERVIEWCONTROLLER_H

This is the RBScannerViewController.h file.

#import "ScannerViewController.h" // This is all that I have added to the original file
#import <UIKit/UIKit.h>

@interface RBScannerViewController : UIViewController {} // I have added the curly brackets here.

@end

This is the RBScannerViewController.mm file that was originally a .m file which i have renamed.

#import "RBScannerViewController.h"
#import <AVFoundation/AVFoundation.h>

//A class extension of RBScanViewController
@interface RBScannerViewController () <AVCaptureMetadataOutputObjectsDelegate>

@property (strong, nonatomic) AVCaptureDevice* device;
@property (strong, nonatomic) AVCaptureDeviceInput* input;
@property (strong, nonatomic) AVCaptureMetadataOutput* output;
@property (strong, nonatomic) AVCaptureSession* session;
@property (strong, nonatomic) AVCaptureVideoPreviewLayer* preview;

@end

@implementation RBScannerViewController 

// This is the slot I have added to the original file. 
void ScannerViewController(void)
{
    viewDidLoad();
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // checking if we have at least one camera device
    NSArray *allTypes = @[AVCaptureDeviceTypeBuiltInDualCamera, AVCaptureDeviceTypeBuiltInWideAngleCamera, AVCaptureDeviceTypeBuiltInTelephotoCamera ];
    AVCaptureDeviceDiscoverySession *discoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:allTypes mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionBack];
    NSArray *devices = discoverySession.devices;
    
    BOOL hasCamera = [devices count] > 0;
    
    if (hasCamera){
        [self setupScanner];
    } else {
        NSLog(@"No Camera available");
    }
}



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

// perform the main setup
- (void) setupScanner {
    
    // creating the camera device
    self.device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    
    // creating the input
    NSError *error = nil;
    self.input = [AVCaptureDeviceInput deviceInputWithDevice:self.device error:&error];
    if (!self.input){
        NSLog(@"error setting up scanner: %@", error);
        return;
    }
    
    // creating the ouput
    self.output = [[AVCaptureMetadataOutput alloc] init];
    
    
    // creating the session (which is responsible for managing the data flow between input/output)
    self.session = [[AVCaptureSession alloc] init];
    [self.session addOutput:self.output];
    [self.session addInput:self.input];
    
    // setting self to be the delegate
    [self.output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    
    // specifying which metadata we want to capture. In this case we are setting it to only look for QR codes.
    self.output.metadataObjectTypes = @[AVMetadataObjectTypeQRCode, AVMetadataObjectTypeEAN13Code];
    
    // Line below lists available metadata for this device.
    //NSLog(@"This device support identifying the following metadatas = %@", [self.output availableMetadataObjectTypes]);
    
    // creating the preview layer
    self.preview = [AVCaptureVideoPreviewLayer layerWithSession:self.session];
    self.preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
    self.preview.frame = CGRectMake(0,0, self.view.frame.size.width, self.view.frame.size.height);
    
    [self.view.layer addSublayer:self.preview];
    
    [self.session startRunning];
    
}


//  AVCaptureMetadataOutputObjectsDelegate  -  here is where the decoding takes place!
- (void) captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
    
    for (AVMetadataObject *metadata in metadataObjects) {
        
        if ([metadata.type isEqualToString:AVMetadataObjectTypeQRCode] | [metadata.type isEqualToString:AVMetadataObjectTypeEAN13Code]) {
            NSLog(@"We found a QR  or EAN13 barcode!");
            
            // Transforming the metadata coordinates to screen coordinates so we can show a rect around it if we want to (not showing it in this simple example)
            AVMetadataMachineReadableCodeObject *transformed = (AVMetadataMachineReadableCodeObject *)[self.preview transformedMetadataObjectForMetadataObject:metadata];
            
            // printing the decoded text to console
            NSLog(@"%@", [transformed stringValue]);
            
        }

    }
    
}
@end

And obviously as expected, the code failed to build.

[SGaist]

I just remembered, and to simplify your life, did you consider using QZXing ? It's a wrapper for the ZXing library that is cross-platform and does barcode scanning.

That would give you a ready made solution that is directly integrated with Qt.

See this excellent KDAB blog entry on the subject.

[TheCrowKaka]

@SGaist HAHAHA :)

I am already using the QZXing library for barcode scanning for Android, Windows and IOS. However, for IOS, because of the bug in https://bugreports.qt.io/browse/QTBUG-98651, I had to upgrade to Qt6.4 as the problem is solved in 6.4. But after I switched the Qt6.4, the QZXing library is giving error in compiling.
I am getting an error. The Build happens successfully, application gets deployed and crashes immediately giving an error.

Error: You are creating QApplication before calling UIApplicationMain.
If you are writing a native iOS application, and only want to use Qt for
parts of the application, a good place to create QApplication is from within
'applicationDidFinishLaunching'
inside your UIApplication delegate.

Though the creator of this library has released version for Qt6.2, still I am getting this error.

Hence I started looking for alternatives and I came across this Objective-C code without using any external library, which I am looking at incorporating with Qt6.4.

I dont have much knowledge of Objective-C and not much data is available on mixing that with Qt6.