我们是否必须在viewDidLoad中或UIViewController中的viewDidLoad外部初始化属性？

Question

I read an article says property needs to be nil when UIViewController class created, and then storyboard or you add it to value when viewDidLoad invoked.

It says properties can not be initialized when object is constructed also.

According to article it would be like below Note that it is custom button not from storyboard.

class BetterViewController: UIViewController {
    var myButton: UIButton!

override func viewDidLoad() {
        super.viewDidLoad()
        myButton = UIButton() // I set value to myButton.
       let anotherVariable = myButton.method // whatever method 
}

Above, myButton was type of nil first and then I set a value to it when viewDidLoad. Everything is okay so far. But I see so many codes like below

class ToDoListVewController: UITableViewController {

    let defaults = UserDefaults.standard  
    var itemArray = [Item]() // 

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        if let items = defaults.array(forKey: "ToDoListArray") as? [String]{
            itemArray = items
        }
    }

Above example, itemArray is not nil. But it needs to be nil when UITableViewController created. So I have to declare itemArray inside viewDidLoad or it is ok? I am confused.

Answer 1

Without any more context, the article is wrong. You obviously can have properties initialised inline, just like the examples you showed. If you want me to explain why the article says that, you should include a link to the article.

Generally, we would like set the property to nil and initialise it in viewDidLoad when the initialisation of the property requires the use of self . Gesture recognisers are a good example of this. We cannot do this:

let myGestureRecognizer = UITapGestureRecognizer(target: self, selector: ...)

because self is used. By the time the above executes, self may not have been constructed properly, so the compiler prohibits this kind of thing. Therefore, we can only set it tot nil:

var myGestureRecognizer: UITapGestureRecognizer!

and initialise it in viewDidLoad :

myGestureRecognizer = UITapGestureRecognizer(target: self, selector: ...)

On the other hand, if the initialisation of the property does not require self to be constructed, you can initialise it inline. For example, if you want to keep track of how many times a user has tapped on a button:

// Without doubt, this will be 0 at the start
var buttonPressedCount = 0