项目中有个需求，需要用到slider控制系统音量，不是视频或者音频播放器，是蓝牙设备播报的音量控制，百度了下千篇一律全是一个方法，可是我试了一下并不好使，网上代码如下：
//1.添加MPVolumeView

MPVolumeView *volumeView = [{MPVolumeView alloc] init];
UISlider *volumeViewSlider = nil;
for (UIView *view in [volumeView subviews]) {
if ([view.class.description isEqualToString:@"MPVolumeSlider"]) {
volumeViewSlider = (UISlider *)view;
break;
}
}
// change system volume, the value is between 0.0f and 1.0f
[volumeViewSlider setValue:0.3f animated:NO];
// send UI control event to make the change effect right now. 立即生效
[volumeViewSlider sendActionsForControlEvents:UIControlEventTouchUpInside];

2.隐藏系统MPVolumeView

volumeView.frame = CGRectMake(-1000, -100, 100, 100);
volumeView.hidden = NO;

3.根据硬件音量键修改音量-添加监听

NSError *error;
[[AVAudioSession sharedInstance] setActive:YES error:&error];
// add event handler, for this example, it is volumeChange: method
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(volumeChanged:) name:@"AVSystemController_SystemVolumeDidChangeNotification" object:nil];

4.然后实现事件回调方法

• (void)volumeChanged:(NSNotification *)notification
  {
  NSDictionary *userInfo = notification.userInfo;
  float value = [[userInfo objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"] floatValue];
  NSLog(@"改变后的数据为：%f",value);
  }

5.//最后记得在资源回收时取消掉事件监听

• (void)dealloc
  {
  [[NSNotificationCenter defaultCenter] removeObserver:self name:@"AVSystemController_SystemVolumeDidChangeNotification" object:nil];
  }

以上的方法中，在硬件音量键修改的时候监听可以获取到，并能进行修改，可是在最初的时候获取不到系统音量。

》》》》》我是转折符《《《《《《《《《《《
看系统API有一个类MPVolumeView，直接两行代码就可以实现这些功能，只是UI展示是slider，也可以自定义设置slider样式，自定义代码如下：
1.先引入框架

import <MediaPlayer/MediaPlayer.h>

2.viewDidLoad中添加方法

• (void)viewDidLoad {
  [super viewDidLoad];
  self.title = @"扫码枪扫描中";
  [self addSoundSliderView];
  }

3.实现方法
//实现
-(void)addSoundSliderView{

MPVolumeView *volumeView = [[MPVolumeView alloc] initWithFrame:CGRectMake(RESIZE(80), RESIZE(70), SCREEN_WIDTH - RESIZE(160), RESIZE(30))];
volumeView.backgroundColor = [UIColor redColor];

//mini线条图片
[volumeView setMinimumVolumeSliderImage:[UIImage imageNamed:@"pickupGoods_volumeMax"] forState:UIControlStateNormal];

//max线条图片
[volumeView setMaximumVolumeSliderImage:[UIImage imageNamed:@"pickupGoods_volumeMin"] forState:UIControlStateNormal];

//中间圆标志
[volumeView setVolumeThumbImage:[UIImage imageNamed:@"pickupGoods_volumeRound"] forState:UIControlStateNormal];
[self.view addSubview:volumeView];

//添加音量小喇叭提示图
[self addSoundImageWithFrame:CGRectMake(RESIZE(50), RESIZE(65), RESIZE(17), RESIZE(27)) withImage:[UIImage imageNamed:@"pickupGoods_volumeDown"]];
//添加音量大喇叭提示图
[self addSoundImageWithFrame:CGRectMake(volumeView.wt_right + RESIZE(10), RESIZE(65), RESIZE(29), RESIZE(26)) withImage:[UIImage imageNamed:@"pickupGoods_volumeUp"]];

}
4.自定义添加喇叭图
-(void)addSoundImageWithFrame:(CGRect )frame withImage:(UIImage *)image{

UIImageView *soundImage = [[UIImageView alloc] init];
soundImage.frame = frame;
soundImage.image = image;
[self.view addSubview:soundImage];

}

如上就可以实现了想要的效果，效果图如下：

WechatIMG68.jpeg

如有更好实现方式欢迎留言，转载请注明出处，谢谢！