Crash while getting the current Autofocus system in ios - ios

Question

There are two types of focus detection right from iphone 6 introduction,
1. Contrast detection
2. Phase detection
from iphone 6.6+ it uses phase detection.
I am trying to get the current focus system
self.format = [[AVCaptureDeviceFormat alloc] init];
[self.currentDevice setActiveFormat:self.format];
AVCaptureAutoFocusSystem currentSystem = [self.format autoFocusSystem];
if (currentSystem == AVCaptureAutoFocusSystemPhaseDetection)
{
[self.currentDevice addObserver:self forKeyPath:#"lensPosition" options:NSKeyValueObservingOptionNew context:nil];
}
else if(currentSystem == AVCaptureAutoFocusSystemContrastDetection)
{
[self.currentDevice addObserver:self forKeyPath:#"adjustingFocus" options:NSKeyValueObservingOptionNew context:nil];
}
else{
NSLog(#"No observers added");
}
but now its crashing in the following line
AVCaptureAutoFocusSystem currentSystem = [self.format autoFocusSystem];
I am unable to find proper description for the crash.

Answer 1

You're creating some "AVCaptureDeviceFormat", but nothing is actually set up by default with it. It's just unusable garbage (and that's why you are getting a crash).
Each capture device has one or two formats it can work with.
You can see them by doing something like:
for (AVCaptureDeviceFormat *format in [self.currentDevice formats]) {
CFStringRef formatName = CMFormatDescriptionGetExtension([format formatDescription], kCMFormatDescriptionExtension_FormatName);
NSLog(#"format name is %#", (NSString *)formatName);
}
What you should be doing is deciding which AVCaptureDevice you want to use (e.g. the front camera, the back camera, whatever), getting the format from that, and then setting [self.currentDevice setActiveFormat:self.format]".
The WWDC 2013 session "What's New in Camera Capture" video has more information on how to do this.