audioSessionGetProperty doesn't work (iOS)

Question

I am trying to detect the current volume, but the result is always 0. this is my codes:

in the view controller.m

1. import the AudioToolbox.

2. in viewDidLoad method, AudioSessionInitialize(NULL, NULL, NULL, NULL);

3. in viewDidLoad method, following the above initialization method.

     Float32 volume_reading;
   

   UInt32 dataSize = sizeof(Float32);

   AudioSessionGetProperty ( kAudioSessionProperty_CurrentHardwareOutputVolume, &dataSize, &volume_reading );

4. po volume_reading in the debugger, result is 0.

Any suggestion? Thanks very much.

Answer 1

This is a somewhat older question, but did you initialize the audio session?

Example:

AudioSessionInitialize(NULL, NULL, NULL, (__bridge void*)self);