Handling Interruptions With AVAudioRecorder

Question

I am using an AVAudioRecorder to check the volume level and accordingly update a UIImageView. However, when I hold the home button down for Siri or when the device receives a phone call, the UIImageView is not updated anymore. This is my current code with this imported in the .h:

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#import <CoreAudio/CoreAudioTypes.h>

I then used this code to create the recorder and update the UIImageView in the .m:

@interface MyViewController ()

@property NSTimer *checkDecibelLevelsTimer;
@property (strong, nonatomic) IBOutlet UIImageView *visualizer;
@property AVAudioRecorder *recorder;

@end

@implementation MyViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    [audioSession setCategory:AVAudioSessionCategoryRecord error:nil];
    [audioSession setActive:YES error:nil];

    NSURL *url = [NSURL fileURLWithPath:@"/dev/null"];
    NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
                          [NSNumber numberWithFloat: 44100.0],                 AVSampleRateKey,
                          [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey,
                          [NSNumber numberWithInt: 1],                         AVNumberOfChannelsKey,
                          [NSNumber numberWithInt: AVAudioQualityMax],         AVEncoderAudioQualityKey,
                          nil];
    NSError *error;

    self.recorder = [[AVAudioRecorder alloc] initWithURL:url settings:settings error:&error];

    if (self.recorder) {
        [self.recorder prepareToRecord];
        self.recorder.meteringEnabled = YES;
        [self.recorder record];
    } else {
        NSLog(@"%@", [error description]);
    }

    self.checkDecibelLevelsTimer = [NSTimer scheduledTimerWithTimeInterval: 0.03
                                                   target: self
                                                 selector: @selector(checkDecibelLevelsCallback:)
                                                 userInfo: nil
                                                  repeats: YES];
}

-(void)checkDecibelLevelsCallback:(NSTimer *)timer {
    [self.recorder updateMeters];
    if ([self.recorder averagePowerForChannel:0] < -40) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer1"];
    } else if ([self.recorder averagePowerForChannel:0] < -35) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer2"];
    } else if ([self.recorder averagePowerForChannel:0] < -30) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer3"];
    } else if ([self.recorder averagePowerForChannel:0] < -25) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer4"];
    } else if ([self.recorder averagePowerForChannel:0] < -20) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer5"];
    } else if ([self.recorder averagePowerForChannel:0] < -15) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer6"];
    } else if ([self.recorder averagePowerForChannel:0] < -10) {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer7"];
    } else {
        self.visualizer.image = [UIImage imageNamed:@"Visualizer8"];
    }
 }

I tried to handle interruptions by implementing this code in the .m:

- (void)beginInterruption {
    NSLog(@"begin interruption");
    [self.recorder pause];
}

- (void)endInterruption {
    NSLog(@"end interruption");
    [self.recorder record];
}

and adding @interface MyViewController : UIViewController <AVAudioSessionDelegate> in the .h. I noticed that the NSLog returns nothing and the UIImageView still is not updated. How can I fix this?

Answer 1

Alright, I figured out a solution. I put this in the viewDidLoad method:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willResignInactive) name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didBecomeActive) name:UIApplicationDidBecomeActiveNotification object:nil];

and added the following methods:

- (void)willResignInactive {
    [self.recorder stop];
}

- (void)didBecomeActive {
    [self.recorder record];
}