+[NSData dataWithContentsOfURL:] will cause NSProgress to report progress.

gistfile1.m

#import <Foundation/Foundation.h>

static void *ProgressObserverContext = &ProgressObserverContext;

@interface MyObject: NSObject

@property (strong, nonatomic) NSProgress *progress;

@end

@implementation MyObject

- (instancetype)init {
	if (self = [super init]) {
		
		self.progress = [NSProgress progressWithTotalUnitCount:1]; 
		
		[self.progress addObserver:self
		   forKeyPath:NSStringFromSelector(@selector(fractionCompleted))
			options:NSKeyValueObservingOptionInitial
			context:ProgressObserverContext];
			
		[self.progress becomeCurrentWithPendingUnitCount:1];
		
		// Either of the following next two lines will cause progress to be reported.
		NSData *data = [NSData dataWithContentsOfURL:[NSURL fileURLWithPath:@"/etc/hosts"]];
		// NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.example.com"]];
		
	}
	return self;
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
						change:(NSDictionary *)change context:(void *)context
{
	if (context == ProgressObserverContext)
	{
		NSProgress *progress = object;
		
		NSLog(@"fraction completed: %f", progress.fractionCompleted);
	}
	else
	{
		[super observeValueForKeyPath:keyPath ofObject:object
							   change:change context:context];
	}
}

@end


int main(int argc, char *argv[]) {
	@autoreleasepool {
		MyObject *object = [[MyObject alloc] init];		
	}
}

To try, just copy and paste into CodeRunner.