Nil Cannot Be Assigned to Type Avcapturedeviceinput

Nil cannot be assigned to type AVCaptureDeviceInput

It makes total sense to me. If you'd like to set it to nil. Use optionals. that way you can set it to nil. It's a good mechanism to avoid crashes and a ton of if statements for null checks. What I recommend (even for testing) is using optionals. This is how it would look like for you:

var deviceInput : AVCaptureDeviceInput?

Now deviceInput does NOT have to hold any valid value. so you could write the following (although it's default to nil)

deviceInput = nil

Now, say you want to use it elsewhere. You could use if let like this:

if let myNonNilValue = deviceInput {
    // myNonNilValue is for sure not nil
}

Xcode 12.5 compiler bug, 'nil' cannot be used in context expecting type 'someType'

Splitting code into two parts helped

var mappedArray: [SomeStruct] = ["123123", "2", "332", "124r132q", "123"].compactMap { $0.count == 3 ? .init(str: $0) : nil }

arr1.append(contentsOf: mappedArray)

AVCaptureSession Runtime crash. fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)

Looking at your code, you should really try to get out of the habit of force-unwrapping optionals using ! at any opportunity, especially just to “make it compile". Generally speaking, if you ever find yourself writing if something != nil, there’s probably a better way to write what you want. Try looking at the examples in this answer for some idioms to copy. You might also find this answer useful for a high-level explanation of why optionals are useful.

AVCaptureDeviceInput.deviceInputWithDevice returns an AnyObject, and you are force-casting it to a AVCaptureInput with this line:

var deviceInput = AVCaptureDeviceInput.deviceInputWithDevice(captureDevice, error: &err) as! AVCaptureInput

(you don’t need to state the type of deviceInput by the way, Swift can deduce it from the value on the right-hand side)

When you write as!, you are telling the compiler “don’t argue with me, force the result to be of type AVCaptureInput, no questions asked”. If it turns out what is returned is something of a different type, your app will crash with an error.

But then on the next line, you write:

if deviceInput == nil! {

I’m actually quite astonished this compiles at all! But it turns out it does, and it’s not surprising it crashes. Force-unwrapping a value that is nil will crash, and you are doing this in it’s purest form, force-unwrapping a nil literal :)

The problem is, you’ve already stated that deviceInput is a non-optional type AVCaptureInput. Force-casting the result is probably not the right thing to do. As the docs for state,

If the device cannot be opened because it is no longer available or because it is in use, for example, this method returns nil, and the optional outError parameter points to an NSError describing the problem.

The right way to handle this is to check is the result is nil, and act appropriately. So you want to do something like:

if let deviceInput = AVCaptureDeviceInput.deviceInputWithDevice(captureDevice, error: &err) as? AVCaptureInput
    // use deviceInput
}
else {
    println("error: \(err?.localizedDescription)")
}

Variables show up as nil - swift 4 IOS

First thing is never use forcefully unwrap until you are sure about value. In your case VNCoreModelRequest can fail and your both variable will be un assigned so it will defiantly crash your app.
One more thing make sure you use proper naming convention to your label.

Your issue is you are not setting label value from result you are getting.

To fix this

 var stringy:String? {
    didSet {
        DispatchQueue.main.async {
            self.Labele.text = self.stringy
        }
    }
}

OR

        self.stringy = firstObservastion.identifier
        self.stringie = firstObservastion.confidence
        DispatchQueue.main.async {
             self.Labele.text = "Guess: \(stringy) + Certainty: \(stringie)"
         }

Bewildered: Non-nil value unwrapped nil, if-let clause executes block on nil value

stillImageData and detailItem are not nil, but imageView is nil.

In prepare(for at the moment you execute controller.detailItem = stillImageData the view of the destination controller is not loaded yet, therefore all outlets are not connected. When the outlet is accessed in configureView() the crash occurs.

In this case call configureView() in viewDidLoad

var detailItem: Data? 

override func viewDidLoad() {
    super.viewDidLoad()
    configureView()
}

On the other hand if detailItem is going to be updated multiple times check the outlet

var detailItem: Data? {
    didSet {
        if imageView != nil { configureView() }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    configureView()
}

Swift Dictionary is nil when adding output settings

You aren't setting imageCaptured to anything. It's nil.

For example how to initialize it, see How To Use AVCaptureStillImageOutput To Take Picture.

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