User guide

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What the previous route was

The keys for the dictionary are AVAudioSessionRouteChangeReasonKey and

AVAudioSessionRouteChangePreviousRouteKey. The various reasons why a hardware audio route might

have changed—accessed by the AVAudioSessionRouteChangeReasonKey key—are listed and described

in AVAudioSessionRouteChangeReason. The previous route information—accessed by the

AVAudioSessionRouteChangePreviousRouteKey key—is an object that describes the audio route setting

from before the route change.

One reason for the audio hardware route change in iOS is

AVAudioSessionRouteChangeReasonCategoryChange. In other words, a change in audio session category

is considered by the system—in this context—to be a route change, and will invoke a route change notification.

As a consequence, if your notification response method is intended to respond only to headset plugging and

unplugging, it should explicitly ignore this type of route change.

Here’s a practical example. A well-written recorder/playback app sets the audio session category when beginning

playback or recording. Because of this, a route-change notification is sent upon starting playback (if you were

previously recording) or upon starting recording (if you were previously playing back). Clearly, such an app

should not pause or stop each time a user taps Record or Play. To avoid inappropriate pausing or stopping,

the method called upon receipt of the notification should branch based on the reason for the route change

and simply return if it was a category change. In this case, the category change is from the system’s perspective

and not the app’s perspective.

Responding to Route Changes

Responding to Audio Hardware Route Changes