AVAudioSession的OutputVolume永远不会改变 [英] AVAudioSession's OutputVolume never changes

问题描述

关于SO的很多问题和答案都说[AVAudioSession sharedInstance].outputVolume是检测设备音量的唯一方法.但这似乎不太正确. outputVolume永远不会更改，尽管第一次设置时是正确的(在应用程序启动时).

There are plenty of questions and answers on SO that say [AVAudioSession sharedInstance].outputVolume is the only way to detect a device's volume. But it doesn't seem to work quite right. outputVolume never changes, though it is correct when it is first set (at application launch).

我做错了吗?除了读取outputVolume的值外，我不知道还能做什么.我的直觉会告诉我这是一个错误，如果不是因为其他人似乎做得很好.我也在iOS 7和8上进行了测试，因此它不是iOS 8的错误.我在一个小型测试项目中复制了相同的内容，因此项目中没有任何干扰.

Am I doing it wrong? I don't know what else to do besides reading the value of outputVolume. My instincts would tell me this was a bug, if it wasn't for the fact that other people seem to be doing it just fine. I also tested it on iOS 7 and 8, so it's not an iOS 8 bug. I reproduced the same thing in a small test project, so nothing in my project is interfering with it.

另外:我很清楚铃声音量和声音音量之间的区别.我都更改了，报告的数量仍然没有变化.

Also: I am well aware of the difference between ringer-volume and sound-volume. I changed both, and the reported volume still did not change.

这是我在测试项目中使用的功能:

Here's the function I used in my test project:

- (void)checkVolume
{
    float volume = [AVAudioSession sharedInstance].outputVolume;

    NSLog(@"Volume: %f", volume);

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^
    {
        [self checkVolume];
    });
}

推荐答案

使用KVO，并确保激活sharedInstance:

Use KVO, and make sure to activate the sharedInstance:

[[AVAudioSession sharedInstance] setActive:YES error:nil];
[[AVAudioSession sharedInstance] addObserver:self forKeyPath:@"outputVolume" options:NSKeyValueObservingOptionNew context:nil];

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