Crash when instantiating ARSCNView for the second time

Question

I have a problem in my iPhone app when trying to instantiate an ARSCNView again, after destroying it.

In my ViewController I programmatically create an ARSCNView for motion capture interaction:

func addARSceneView() {
    arSceneView = ARSCNView(frame: self.view.frame)
    arSceneView.loops = true
    arSceneView.session.delegate = self
    self.view.addSubview(arSceneView)
    arSceneView.session.run(ARBodyTrackingConfiguration())
}

When the user leaves this part of the app, I tear it down like this:

func removeARSceneView() {
    arSceneView.session.pause()
    arSceneView.pause(self)
    arSceneView.session.delegate = nil
    arSceneView.removeFromSuperview()
    arSceneView = nil
}

Later, when I try to instantiate an ARSCNView for the second time using the first function above, it crashes with an EXC_BAD_ACCESS in the constructor:

I also tried to use a view from a xib which contains an ARSCNView but the same problem occurs, in that case in the init(coder) function of that view.

I found nothing on this problem, I guess usually developers only create an ARSCNView once.

Answer 1

TLDR: Turn "Metal API Validation" on in your scheme.

I found the culprit, after creating a sample project with only the ARSCNView, which did not have this problem. I started by stripping everything away from my original project until it was as barebones as the sample. That did not solve it, so I compared every little setting of the two, and behold: in the "Run" scheme of the original project, under "Diagnostics", I had "Metal – API Validation" ticked off. I don't remember when and why I did that; I assume it was some attempt to improve performance at one point. However, enabling this checkbox solved the problem completely.