Obj. C - QR Reading application runs too slow - ios

Question

I made an QR Code reading application with AVFoundation by tutorial on this site (tutorial of Appcoda). After reading QR code, the app shows an UIAlertView. But it takes nearly 2 minutes (sometimes more than 3mins). I'll paste the whole ViewController.m file here. I hope it is enough. (UIAlertView is in captureOutput method)
//
// ViewController.m
// Yuvio
//
// Created by İhsan Batuğhan YILMAZ on 29/08/15.
// Copyright © 2015 Farabius. All rights reserved.
//
#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>
#interface ViewController ()
#property (nonatomic) BOOL isReading;
#property (nonatomic, strong) AVCaptureSession *captureSession;
#property (nonatomic, strong) AVCaptureVideoPreviewLayer *videoPreviewLayer;
-(BOOL)startReading;
-(void) stopReading;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
_isReading=NO;
_captureSession = nil;
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(IBAction)startStopReading:(id)sender {
if (!_isReading) {
if ([self startReading]) {
[_btnStart setTitle:#"Stop"];
}
}
else{
[self stopReading];
[_btnStart 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 setMetadataObjectTypes:[NSArray arrayWithObject:AVMetadataObjectTypeQRCode]];
_videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
[_videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
[_videoPreviewLayer setFrame:_cameraView.layer.bounds];
[_cameraView.layer addSublayer:_videoPreviewLayer];
[_captureSession startRunning];
return YES;
}
-(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]) {
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:#"QR Detected"
message:[metadataObj stringValue]
delegate:self
cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
[self performSelectorOnMainThread:#selector(stopReading) withObject:nil waitUntilDone:NO];
[_btnStart performSelectorOnMainThread:#selector(setTitle:) withObject:#"Start!" waitUntilDone:NO];
_isReading = NO;
}
}
}
-(void)stopReading{
[_captureSession stopRunning];
_captureSession = nil;
[_videoPreviewLayer removeFromSuperlayer];
return;
}
#end

Answer 1

I think that problem is in using UI functions outside main thread. Try this code:
-(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]) {
__weak ViewController *weakSelf = self;
dispatch_async(dispatch_get_main_queue(), ^{
[weakSelf processQRCode:metadataObj];
});
}
}
}
-(void)processQRCode:(AVMetadataMachineReadableCodeObject *)codeObject{
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:#"QR Detected"
message:[codeObject stringValue]
delegate:self
cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
[self stopReading];
[_btnStart setTitle:#"Start!" forState:UIControlStateNormal];
_isReading = NO;
}
I checked your view controller with this fix and it works fast.