iOS-设置系统音量及监听

1.设置系统音量

    MPVolumeView *volumeView = [MPVolumeView new];
    volumeView.showsRouteButton = NO;
    volumeView.showsVolumeSlider = NO;
    [self.view addSubview:volumeView];
    __weak __typeof(self)weakSelf = self;
    [[volumeView subviews] enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        if ([obj isKindOfClass:[UISlider class]]) {
            __strong __typeof(weakSelf)strongSelf = weakSelf;
            strongSelf.volumeSlider = obj;
            *stop = YES;
        }
    }];
    [self.volumeSlider setValue:1.0 animated:YES];

2.注册通知

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(volumeChanged:) name:@"AVSystemController_SystemVolumeDidChangeNotification" object:nil];

3.监听通知

-(void)volumeChanged:(NSNotification *)notification{
    float volume = [[[notification userInfo] objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"] floatValue];
    NSLog(@"FlyElephant-系统音量:%f", volume);
}

4.移除通知

    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"AVSystemController_SystemVolumeDidChangeNotification" object:nil];