iOS监听音量按键

#import <AVFoundation/AVFoundation.h>

- (void)addVolumeObserver
{
    AVAudioSession *audioSession = [AVAudioSession sharedInstance];
    NSError *error = nil;
    [audioSession setActive:YES error:&error];
    if (error) {
        NSLog(@"%@", error);
    }
    [audioSession addObserver:self forKeyPath:@"outputVolume" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
{
    if (![keyPath isEqualToString:@"outputVolume"]) {
        return;
    }
    
    NSKeyValueChangeKey newValue = change[@"new"];
    NSKeyValueChangeKey oldValue = change[@"old"];
    NSLog(@"oldValue=%@ newValue=%@", oldValue, newValue);
}