ios - 什么时候发布 AVCaptureDeviceSubjectAreaDidChangeNotification？

Question

在 Apple 的示例代码“AVCam”中，AVCaptureDeviceSubjectAreaDidChangeNotification 被添加到 NSNotificationCenter，但它的回调“subjectAreaDidChange”从未在我的测试中被调用。请问系统什么时候会发出这个通知？

通过以下代码添加:

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(subjectAreaDidChange:)
                                             name:AVCaptureDeviceSubjectAreaDidChangeNotification
                                           object:[[self videoDeviceInput] device]];

而AVFoundation的头文件AVCaptureDevice.h如下:

@constant  AVCaptureDeviceSubjectAreaDidChangeNotification
@abstract
   Posted when the instance of AVCaptureDevice has detected a substantial change to the 
   video subject area.
@discussion
   Clients may observe the AVCaptureDeviceSubjectAreaDidChangeNotification to know when an
   instance of AVCaptureDevice has detected a substantial change to the video subject area.
   This notification is only sent if you first set subjectAreaChangeMonitoringEnabled to
   YES.

这就是我的全部问题。非常感谢。

Answer 1

你设置了吗

[[self videoDeviceInput] device].subjectAreaChangeMonitoringEnabled = YES;