I use Vuforia SDK, version 6.2.9 in my iOS App. All work's fine, but there is an error when the app enter from background.

The viewcontroller running VUFORIA is listening for UIApplicationWillResignActiveNotification and UIApplicationDidBecomeActiveNotification notifications. In the case of UIApplicationWillResignActiveNotification pause AR, in the case of UIApplicationDidBecomeActiveNotification resume AR.

// we use the iOS notification to pause/resume the AR when the application goes (or come back from) background

[[NSNotificationCenter defaultCenter]

addObserver:self

selector:@selector(pauseAR)

name:UIApplicationWillResignActiveNotification

object:nil];

[[NSNotificationCenter defaultCenter]

addObserver:self

selector:@selector(resumeAR)

name:UIApplicationDidBecomeActiveNotification

object:nil];

These are the methods

- (void) pauseAR {

   NSError * error = nil;

   if (![vapp pauseAR:&error]) {

      NSLog(@"Error pausing AR:%@", [error description]);

   }

}

- (void) resumeAR {

    NSError * error = nil;

    if(! [vapp resumeAR:&error]) {

        NSLog(@"Error resuming AR:%@", [error description]);

    }

    // on resume, we reset the flash

    Vuforia::CameraDevice::getInstance().setFlashTorchMode(false);

    [self handleRotation:self.interfaceOrientation];

}

When I return to the scan mode, after the app has entered from background, the camera is frozen, with error 

Could not find a UIView with CAEAGLLayer or CAMetalLayer layer class that responds to selector renderFrameVuforia

2017-07-17 11:13:01.187406+0200 App[8689:2961061] frame: {{0, 0}, {375, 667}}

2017-07-17 11:13:01.243707+0200 App[8689:2961061] DEBUG/AR(8689) Could not find a UIView with CAEAGLLayer or CAMetalLayer layer class that responds to selector renderFrameVuforia

2017-07-17 11:13:01.253958+0200 App[8689:2961061] Vuforia Library version 6.2.9

2017-07-17 11:13:01.731099+0200 App[8689:2961061] AR View: Rotating to Portrait

2017-07-17 11:13:01.731406+0200 App[8689:2961061] frame: {{0, 0}, {375, 667}}

2017-07-17 11:13:01.731562+0200 App[8689:2961061] VideoBackgroundConfig: size: 750,1334

2017-07-17 11:13:01.731589+0200 App[8689:2961061] VideoMode:w=1280 h=720

2017-07-17 11:13:01.731611+0200 App[8689:2961061] width=750.000 height=1334.000

2017-07-17 11:13:01.731638+0200 App[8689:2961061] ViewPort: X,Y: 0,0 Size X,Y:750,1334

2017-07-17 11:13:02.598959+0200 App[8689:2962160] INFO/AR(8689) 2017-07-18 11:13:02: Completed CloudReco transaction with ID '6f5c61ecc07741a7b652242abf909479'

2017-07-17 11:13:02.843834+0200 App[8689:2961061] frame: {{0, 0}, {375, 667}}

2017-07-17 11:13:02.844215+0200 App[8689:2961061] frame: {{0, 0}, {375, 667}}

2017-07-17 11:13:02.860971+0200 App[8689:2961061] DEBUG/AR(8689) UIView has CAEAGLLayer layer class

2017-07-17 11:13:02.861114+0200 App[8689:2961061] DEBUG/AR(8689) UIView does not respond to selector renderFrameVuforia

2017-07-17 11:13:02.861191+0200 App[8689:2961061] DEBUG/AR(8689) UIView has CAEAGLLayer layer class

2017-07-17 11:13:02.861222+0200 App[8689:2961061] DEBUG/AR(8689) UIView does not respond to selector renderFrameVuforia

Thanks for your help!