Unable to "pop" view controller using "Show" segue in XCode 6 - objective-c

Question

I have an app that allows you to scan a QR code for meta data. The root view controller has two text fields, and allows you to fill one of those fields with the scanner. The button to access the scanner uses the "Show" segue to push the Scanning view onto the navigation stack.
My intention is that once a valid scan has been completed, the view controller will pass data back to the parent controller, and then be removed.
Being that the view has been pushed, I should be able to implement popViewControllerAnimated, but this does not work. I have also tried iterating through the view controllers in the navigation stack, matching the class I'm trying to pop to and using popToViewController, but am still stuck with the view that I'm trying to pop off the stack.
My viewcontroller.m
#interface ScanQRViewController ()
#end
#implementation ScanQRViewController
#synthesize scanPreview, scanPreviewLayer, scanSession, addyString, delegate;
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
scanSession = nil;
[self startScanning];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark QR code scanning
-(void)startScanning {
addyString = nil;
NSError *error;
// create capture device and input
AVCaptureDevice *capDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:capDevice error:&error];
// error checking
if(!input) {
NSLog(#"%#", [error localizedDescription]);
}
// init the capture session
scanSession = [[AVCaptureSession alloc] init];
[scanSession addInput:input];
AVCaptureMetadataOutput *metaOutput = [[AVCaptureMetadataOutput alloc] init];
[scanSession addOutput:metaOutput];
// assign to dispatch queue
dispatch_queue_t dispatchQueue;
dispatchQueue = dispatch_queue_create("qrQueue", NULL);
[metaOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
[metaOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
// create camera view for user
scanPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:scanSession];
[scanPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
[scanPreviewLayer setFrame:scanPreview.layer.bounds];
[scanPreview.layer addSublayer:scanPreviewLayer];
// start running sesssion
[scanSession startRunning];
}
- (void)stopScanning {
[scanSession stopRunning];
scanSession = nil;
[scanPreviewLayer removeFromSuperlayer];
}
#pragma mark AV Delegate Methods
-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
// check for objects
if (metadataObjects != nil && [metadataObjects count] > 0) {
//get the last object
AVMetadataMachineReadableCodeObject *metaObj = [metadataObjects objectAtIndex:0];
if([[metaObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
// remove url string if exists
if ([[[metaObj stringValue] substringToIndex:9] isEqualToString:#"zetacoin:"]) {
addyString = [[metaObj stringValue] substringFromIndex:9];
} else {
addyString = [metaObj stringValue];
}
}
[self stopScanning];
[self dismissView];
}
}
#pragma mark - Navigation
- (void)dismissView {
[delegate ScanQRCodeDidFinish:self];
[self.navigationController popViewControllerAnimated:YES];
}
#end

Answer 1

So I figured out the issue to this problem. Essentially when passing the data back to the parent controller to the delegate, I wasn't on the main thread. Therefore it would eventually timeout and return to the view, but very slowly. My two views:
QRScanner.m < The scanning view
#interface ScanQRViewController ()
#end
#implementation ScanQRViewController
#synthesize scanPreview, scanPreviewLayer, scanSession, addyString, delegate;
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
scanSession = nil;
[self startScanning];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark QR code scanning
-(void)startScanning {
addyString = nil;
NSError *error;
// create capture device and input
AVCaptureDevice *capDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:capDevice error:&error];
// error checking
if(!input) {
NSLog(#"%#", [error localizedDescription]);
}
// init the capture session
scanSession = [[AVCaptureSession alloc] init];
[scanSession addInput:input];
AVCaptureMetadataOutput *metaOutput = [[AVCaptureMetadataOutput alloc] init];
[scanSession addOutput:metaOutput];
// assign to dispatch queue
dispatch_queue_t dispatchQueue;
dispatchQueue = dispatch_queue_create("qrQueue", NULL);
[metaOutput setMetadataObjectsDelegate:self queue:dispatchQueue];
[metaOutput setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
// create camera view for user
scanPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:scanSession];
[scanPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
[scanPreviewLayer setFrame:scanPreview.layer.bounds];
[scanPreview.layer addSublayer:scanPreviewLayer];
// start running sesssion
[scanSession startRunning];
}
- (void)stopScanning {
[scanSession stopRunning];
scanSession = nil;
[scanPreviewLayer removeFromSuperlayer];
}
#pragma mark AV Delegate Methods
-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
// check for objects
if (metadataObjects != nil && [metadataObjects count] > 0) {
//get the last object
AVMetadataMachineReadableCodeObject *metaObj = [metadataObjects objectAtIndex:0];
if([[metaObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
// remove url string if exists
if ([[[metaObj stringValue] substringToIndex:9] isEqualToString:#"zetacoin:"]) {
addyString = [[metaObj stringValue] substringFromIndex:9];
} else {
addyString = [metaObj stringValue];
}
}
[self stopScanning];
[self dismissView];
}
}
#pragma mark - Navigation
- (void)dismissView {
NSLog(#"%#", self.navigationController);
[delegate ScanQRCodeDidFinish:self];
}
#end
AddAddress.m < The view I was trying to return to
#import "AddAddressViewController.h"
#import "ScanQRViewController.h"
#interface AddAddressViewController ()
#end
#implementation AddAddressViewController
#synthesize nameField, addressField, addressText;
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.navigationController.navigationItem.backBarButtonItem.title = #"Back";
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (void)viewWillAppear:(BOOL)animated {
// check to see if there's an address (QR) add to text field
if (addressText != nil) {
addressField.text = addressText;
NSLog(#"Address: %#", addressText); // debugging
}
}
#pragma mark delegate methods
- (void)ScanQRCodeDidFinish:(ScanQRViewController *)sqrvc {
if (![NSThread isMainThread]) {
dispatch_sync(dispatch_get_main_queue(), ^{
addressField.text = sqrvc.addyString;
[self.navigationController popViewControllerAnimated:YES];
});
} else {
addressField.text = sqrvc.addyString;
[self.navigationController popViewControllerAnimated:YES];
}
}
#pragma mark - Navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
ScanQRViewController *sqvc = [segue destinationViewController];
sqvc.delegate = self;
}
#end
By adding the dispatch_sync(dispatch_get_main_queue(), ^{ it executed on the main thread and returned back the view as expected.