AVCaptureDevice的几个属性

enum {
    AVCaptureDevicePositionBack = 1,
    AVCaptureDevicePositionFront = 2
};
typedef NSInteger AVCaptureDevicePosition;

enum {
    AVCaptureFlashModeOff = 0,
    AVCaptureFlashModeOn = 1,
    AVCaptureFlashModeAuto = 2
};
typedef NSInteger AVCaptureFlashMode;

enum {
    AVCaptureTorchModelOff = 0,
    AVCaptureTorchModelOn = 1,
    AVCaptureTorchModeAuto = 2
};
typedef NSInteger AVCaptureTorchMode;

enum {
    AVCaptureFocusModelLocked = 0,
    AVCaptureFocusModeAutoFocus = 1,
    AVCaptureFocusModeContinousAutoFocus = 2
};
typedef NSInteger AVCaptureFocusMode;

enum {
    AVCaptureExposureModeLocked = 0,
    AVCaptureExposureModeAutoExpose = 1,
    AVCaptureExposureModeContinuousAutoExposure = 2
};
typedef NSInteger AVCaptureExposureMode;

enum {
    AVCaptureWhiteBalanceModeLocked = 0,
    AVCaptureWhiteBalanceModeAutoWhiteBalance = 1,
    AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance = 2
};
typedef NSInteger AVCaptureWhiteBalanceMode; 

AVCaptureDevice* d = nil; // find a device by position
NSArray* allDevices = [AVCaptureDevice devices]; 
for (AVCaptureDevice* currentDevice in allDevices) 
{   
       if (currentDevice.position == AVCaptureDevicePositionBack) 
       {     
               d = currentDevice;   
       } 
} 

// at this point, d may still be nil, assuming we found something we like.... 
NSError* err = nil; 
BOOL lockAcquired = [d lockForConfiguration:&err]; 
if (!lockAcquired) {    
       // log err and handle... 
} else {   
      // flip on the flash mode    
      if ([d hasFlash] && [d isFlashModeSupported:AVCaptureFlashModeOn] ) 
      {       
             [d setFlashMode:AVCaptureFlashModeOn];    
      }

    [d unlockForConfiguration]; 
}