Cannot Form Weak Reference to Instance of Class Nstextview

Cannot form weak reference to instance of class NSTextView

Use @IBOutlet var scrollView: NSScrollView instead of @IBOutlet var textField: NSTextView.

Then create a property returns documentView in scrollView.

import Cocoa

class AppDelegate: NSObject, NSApplicationDelegate {

    @IBOutlet var window: NSWindow
    @IBOutlet var scrollView: NSScrollView

    var textField: NSTextView {
        get {
            return scrollView.contentView.documentView as NSTextView
        }
    }

    @IBAction func displaySomeText(AnyObject) {
        textField.insertText("A string...")
    }

    func applicationDidFinishLaunching(aNotification: NSNotification?) {
        // Insert code here to initialize your application
    }

    func applicationWillTerminate(aNotification: NSNotification?) {
        // Insert code here to tear down your application
    }
}

Which iOS classes that don't support zeroing weak references?

If you try to form a weak reference to an object that doesn't support weak references, the program should die immediately. This is mentioned in the Objective-C Advancements in Depth video from WWDC 2011. So you should know immediately if you find a class that doesn't support them.

I'm pretty sure the lack of mention in Transitioning to ARC Release Notes means that all UIKit classes are safe. I'm not sure if the warning about AV Foundation classes applies to iOS or not. I tested creating a weak reference to AVCaptureSession on both iOS 5 and Lion and neither crashed. I tested creating a weak reference to an NSWindow on Lion and it crashed with the message cannot form weak reference to instance (0x102232ef0) of class NSWindow.

weak property for delegate cannot be formed

According to Apple's Transitioning to ARC Release Notes,

You cannot currently create weak references to instances of the following classes:

NSATSTypesetter, NSColorSpace, NSFont, NSMenuView, NSParagraphStyle, NSSimpleHorizontalTypesetter, and NSTextView.

Note: In addition, in OS X v10.7, you cannot create weak references to instances of NSFontManager, NSFontPanel, NSImage, NSTableCellView, NSViewController, NSWindow, and NSWindowController. In addition, in OS X v10.7 no classes in the AV Foundation framework support weak references.

(Note: one needs to be very careful with nonzeroing weak references...)

unsafe_unretained vs weak : crash during setDelegate

I found the answer: as said in weak property for delegate cannot be formed

You cannot currently create zeroing-weak references to instances of the following classes (emphasis mine):

NSATSTypesetter, NSColorSpace, NSFont, NSFontManager, NSFontPanel, NSImage, NSMenuView, NSParagraphStyle, NSSimpleHorizontalTypesetter, NSTableCellView, NSTextView, NSViewController, NSWindow, and NSWindowController. In addition, in OS X no classes in the AV Foundation framework support weak references.

For declared properties, you should use assign instead of weak; for variables you should use __unsafe_unretained instead of __weak.

In addition, you cannot create weak references from instances of NSHashTable, NSMapTable, or NSPointerArray under ARC.

Strong and weak references in Swift

Straight from the Swift Language guide:

class Person {
    let name: String
    init(name: String) { self.name = name }
    var apartment: Apartment?
    deinit { println("\(name) is being deinitialized") }
}

class Apartment {
    let number: Int
    init(number: Int) { self.number = number }
    weak var tenant: Person?
    deinit { println("Apartment #\(number) is being deinitialized") }
}

properties are strong by default. But look at the tenant property of the class "Apartment", it is declared as weak. You can also use the unowned keyword, which translates to unsafe_unretained from Objective-C

https://itunes.apple.com/tr/book/swift-programming-language/id881256329?mt=11

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