Swift与对象的属性观察器

Question

I'm trying to add a property observer in my class ChooserListVC for "list"

These are the variables in ChooserSaves that I would like to track.

class ChooserSaves: UIDocument {
var savedListObject : SavedList?
var listName : String = ""
var chooserItems : [String] = []
}

Im not sure how to set this up in the class I'm implementing it.

class ChooserListVC: UIViewController, UITableViewDelegate, UITableViewDataSource,UITextFieldDelegate{
var list : ChooserSaves!

I tried to do something like this:

var list : ChooserSaves!{
    didSet{
        if chooserItems.count > 0{
            println("didset greater than 1")
        }
        else{
            println("didset less than 1")
        }
    }
}

But this only works once when the segue assigns the list. How can I make it so that every time I change list.chooserItems in other bits of code, it would trigger the correct line?

Answer 1

The easiest solution would be to set your property you want to observe to private and create publicly available methods to manipulate your array.

...
private var chooserItems: [String] = []
...
func add(chooserItem: String){
    // your tracking logic here

    // update your private array
    self.chooserItems.append(chooserItem)
    ...
}
...

If you need real observation, I'd suggest to checkout this answer Is key-value observation (KVO) available in Swift?

Answer 2

I didn't find it the way I wanted, but I found a different way to do it. I added notifications in the class I was implementing. Then I just added a listener to trigger the event I needed.

class ChooserSaves: UIDocument {
var savedListObject : SavedList?
var listName : String = ""
var chooserItems : [String] = []{
    didSet{
        if chooserItems.isEmpty{
            NSNotificationCenter.defaultCenter().postNotificationName(listEmpty, object: nil)
        }
        else{
            NSNotificationCenter.defaultCenter().postNotificationName(listNotEmpty, object: self)
        }
    }
}

and this was how added the listener in the class I used the object in.

NSNotificationCenter.defaultCenter().addObserver(self, selector: "deactivateControls", name: listEmpty, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "activateControls", name: listNotEmpty, object: nil)