iOS设备闪光灯控制

很多时候都需要在APP中控制闪光灯的开关状态，譬如扫描二维码。控制iOS设备的闪光灯代码非常简单，短短几行代码就可以搞定：

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error;
if (device.hasTorch) {  // 判断设备是否有散光灯
    BOOL b = [device lockForConfiguration:&error];
    if (!b) {
        if (error) {
            DLog(@"lock torch configuration error:%@", error.localizedDescription);
        }
        return;
    }
    device.torchMode =
    (device.torchMode == AVCaptureTorchModeOff ? AVCaptureTorchModeOn : AVCaptureTorchModeOff);
    [device unlockForConfiguration];
}