ios - How to take a photo on the volume-up event when using UIImagePickerController with custom camera controls?

Question

In iOS 5, the volume-up button will now take a photo in the camera app, and on a UIImagePickerController instance where .showsCameraControlls == YES. Happy days.

However, when I set showsCameraControlls to NO, and supply my own (which in turn triggers takePicture method), the volume-up button will no longer work. How can I detect the volume event while the UIImagePickerController is showing?

The old way to detect volume changes was like so:

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

I added this code to my application delegate. Strangely volumeChanged: is not triggered until after I show the UIImagePickerController for the first time. More importantly, it isn't triggered while the UIImagePickerController is visible (nor is the usual volume HUD shown), I guess since Apple disabled it & hijacked the event.

So once again, is there any way to detect the volume-up button event, while the UIImagePickerController is being displayed, when using custom camera controls, for the purpose of taking a photo?

If you're wondering why I need to use custom camera controls, it is because I want the ability to take multiple photos, which the standard camera controls do not allow.

Answer 1

On iOS 8 you can add an observer to the notification _UIApplicationVolumeUpButtonDownNotification

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

If you are using UIImagePickerController, I was able to capture the event and use it to call TakePicture with a custom view.

On top of that, UIImagePickerController ensures that pressing volume up won't change the volume.

I'm not sure if Apple would approve an app listening to that notification; this seems to be the cleanest approach.