SwiftUI - Execute Vision functions on button tap

Question

So I'm trying to use Vision + CoreML in an app, and yes sure, it works as expected using Apple's Resnet50 Model. However, I wish to only use Vision when the user taps a button. I believe this is the function that can detect what the object is:

private func setupVision() {
    guard let model = try? VNCoreMLModel(for: visionClassifier.model) else { return }
    request = VNCoreMLRequest(model: model) { (finishedReq, err) in

        // Get the results list and the first observation
        guard let results = finishedReq.results as? [VNClassificationObservation] else { return }
        guard let firstObservation = results.first else { return }
        
        // Format string output
        let name: String = firstObservation.identifier
        let conf: String = "Confidence: \(firstObservation.confidence * 100)"
        
        // Return the results from the background thread to the main thread
        DispatchQueue.main.async {
            self.identifier = name
            self.confidence = conf
        }
    }
}

So you might think just call that function inside your view, however, this function is called on the .onAppear() method:

  func prepareCapture() {
        setupSession()
        setupVision()
        startSession()
    }

If I take out the setupVision() function, my app will crash at this line:

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

   
    // The captured video frame is stored in a CVPixelBuffer object
    guard let pixelBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }
    
    // Use a VNImageRequestHandler to perform the request
    try? VNImageRequestHandler(cvPixelBuffer: pixelBuffer, options: [:]).perform([request])
    //This line causes a crash
    
}

What can I do to implement a snap and scan feature? Should I allow users to take a picture (without presenting it to them) and handle the rest similar to when using CoreML with an ImagePicker?

Any help would be great!