Global variable is not being updated fast enough 50% of the time - ios

Question

I have a photo taking app. When the user presses the button to take a photo, I set a global NSString variable called self.hasUserTakenAPhoto equal to YES. This works perfectly 100% of the time when using the rear facing camera. However, it only works about 50% of the time when using the front facing camera and I have no idea why.
Below are the important pieces of code and a quick description of what they do.
Here is my viewDidLoad:
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
self.topHalfView.frame = CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height/2);
self.takingPhotoView.frame = CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height);
self.afterPhotoView.frame = CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height);
self.bottomHalfView.frame = CGRectMake(0, 240, self.view.bounds.size.width, self.view.bounds.size.height/2);
PFFile *imageFile = [self.message objectForKey:#"file"];
NSURL *imageFileURL = [[NSURL alloc]initWithString:imageFile.url];
imageFile = nil;
self.imageData = [NSData dataWithContentsOfURL:imageFileURL];
imageFileURL = nil;
self.topHalfView.image = [UIImage imageWithData:self.imageData];
//START CREATING THE SESSION
self.session =[[AVCaptureSession alloc]init];
[self.session setSessionPreset:AVCaptureSessionPresetPhoto];
self.inputDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error;
self.deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:self.inputDevice error:&error];
if([self.session canAddInput:self.deviceInput])
[self.session addInput:self.deviceInput];
_previewLayer = [[AVCaptureVideoPreviewLayer alloc]initWithSession:_session];
self.rootLayer = [[self view]layer];
[self.rootLayer setMasksToBounds:YES];
[_previewLayer setFrame:CGRectMake(0, 240, self.rootLayer.bounds.size.width, self.rootLayer.bounds.size.height/2)];
[_previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
[self.rootLayer insertSublayer:_previewLayer atIndex:0];
self.videoOutput = [[AVCaptureVideoDataOutput alloc] init];
self.videoOutput.videoSettings = #{ (NSString *)kCVPixelBufferPixelFormatTypeKey : #(kCVPixelFormatType_32BGRA) };
[self.session addOutput:self.videoOutput];
dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);
[self.videoOutput setSampleBufferDelegate:self queue:queue];
[_session startRunning];
}
The Important part of viewDidLoad starts where I left the comment of //START CREATING THE SESSION
I basically create the session and then start running it. I have set this view controller as a AVCaptureVideoDataOutputSampleBufferDelegate, so as soon as the session starts running then the method below starts being called as well.
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
fromConnection:(AVCaptureConnection *)connection
{
//Sample buffer data is being sent, but don't actually use it until self.hasUserTakenAPhoto has been set to YES.
NSLog(#"Has the user taken a photo?: %#", self.hasUserTakenAPhoto);
if([self.hasUserTakenAPhoto isEqualToString:#"YES"]) {
//Now that self.hasUserTakenAPhoto is equal to YES, grab the current sample buffer and use it for the value of self.image aka the captured photo.
self.image = [self imageFromSampleBuffer:sampleBuffer];
}
}
This code is receiving the video output from the camera every second, but I don't actually do anything with it until self.hasUserTakenAPhoto is equal to YES. Once that has a string value of YES, then I use the current sampleBuffer from the camera and place it inside my global variable called self.image
So, here is when self.hasUserTakenAPhoto is actually set to YES.
Below is my IBAction code that is called when the user presses the button to capture a photo. A lot happens when this code runs, but really all that matters is the very first statement of: self.hasUserTakenAPhoto = #"YES";
-(IBAction)stillImageCapture {
self.hasUserTakenAPhoto = #"YES";
[self.session stopRunning];
if(self.inputDevice.position == 2) {
self.image = [self selfieCorrection:self.image];
} else {
self.image = [self rotate:UIImageOrientationRight];
}
CGFloat widthToHeightRatio = _previewLayer.bounds.size.width / _previewLayer.bounds.size.height;
CGRect cropRect;
// Set the crop rect's smaller dimension to match the image's smaller dimension, and
// scale its other dimension according to the width:height ratio.
if (self.image.size.width < self.image.size.height) {
cropRect.size.width = self.image.size.width;
cropRect.size.height = cropRect.size.width / widthToHeightRatio;
} else {
cropRect.size.width = self.image.size.height * widthToHeightRatio;
cropRect.size.height = self.image.size.height;
}
// Center the rect in the longer dimension
if (cropRect.size.width < cropRect.size.height) {
cropRect.origin.x = 0;
cropRect.origin.y = (self.image.size.height - cropRect.size.height)/2.0;
NSLog(#"Y Math: %f", (self.image.size.height - cropRect.size.height));
} else {
cropRect.origin.x = (self.image.size.width - cropRect.size.width)/2.0;
cropRect.origin.y = 0;
float cropValueDoubled = self.image.size.height - cropRect.size.height;
float final = cropValueDoubled/2;
finalXValueForCrop = final;
}
CGRect cropRectFinal = CGRectMake(cropRect.origin.x, finalXValueForCrop, cropRect.size.width, cropRect.size.height);
CGImageRef imageRef = CGImageCreateWithImageInRect([self.image CGImage], cropRectFinal);
UIImage *image2 = [[UIImage alloc]initWithCGImage:imageRef];
self.image = image2;
CGImageRelease(imageRef);
self.bottomHalfView.image = self.image;
if ([self.hasUserTakenAPhoto isEqual:#"YES"]) {
[self.takingPhotoView setHidden:YES];
self.image = [self screenshot];
[_afterPhotoView setHidden:NO];
}
}
So basically the viewDidLoad method runs and the session is started, the session is sending everything the camera sees to the captureOutput method, and then as soon as the user presses the "take a photo" button we set the string value of self.hasUserTakenAPhoto to YES, the session stops, and since self.hasUserTakenAPhoto is equal to YES now, the captureOutput method places the very last camera buffer into the self.image object for me to use.
I just can't figure this out because like I said it works 100% of the time when using the rear facing camera. However, when using the front facing camera it only works 50% of the time.
I have narrowed the problem down to the fact that self.hasUserTakenAPhoto does not update to YES fast enough when using the ront facing camera, and I know because if you look in my 2nd code I posted it has the statement of NSLog(#"Has the user taken a photo?: %#", self.hasUserTakenAPhoto);.
When this works correctly, and the user has just pressed the button to capture a photo which also stops the session, the very last time that NSLog(#"Has the user taken a photo?: %#", self.hasUserTakenAPhoto); runs it will print with the correct value of YES.
However, when it doesn't work correctly and doesn't update fast enough, the very last time it runs it still prints to the log with a value of null.
Any ideas on why self.hasUserTakenAPhoto does not update fast enough 50% of the time whe using the front facing camera? Even if we can't figure that out, it doesn't matter. I just need help then coming up with an alternate solution to this.
Thanks for the help.

Answer 1

I think its a scheduling problem. At the return point of your methods
– captureOutput:didOutputSampleBuffer:fromConnection:
– captureOutput:didDropSampleBuffer:fromConnection:
add a CFRunLoopRun()