Retain Cycle (Strong Reference) Fix for Custom Uitextfield

What holds strong reference onto my viewController?

You can use profile the code with Instruments. In Xcode, select Product > Profile. When Instruments loads, select Allocations as the template.

This will allow you to trace which objects are setting what strong references.

Swift: Why aren't my UITextFieldDelegate methods being called?

In UITextField, delegate is declared as a weak property.

weak var delegate: UITextFieldDelegate? { get set }

This means that it doesn't retain the delegate instance and will be set to nil when the delegate is freed.

You are creating the delegate and assigning it to a local variable myTextFieldDelegate. That variable will be freed at the end of the function, so even though you assigned myTextFieldDelegate to the myTextField.delegate, it is freed and myTextField.delegate gets set to nil because it is weak.

To fix this, create a property in your ViewController to hold the delegate object:

var myTextFieldDelegate: MyTextFieldDelegate?

Deallocate view controllers in navigation controller that have a reference to self

As the other answers have said you need to make it a weak reference like this:

weak var controller: UIViewControler?

However I would go further and say that you should not be keeping a reference to to a UIViewController inside any UIView based object (UIImageView, UITextField, etc). The UIViews should not need to know anything about their UIViewControllers.

Instead you should be using a delegation pattern. This is a basic example:

1) Create a protocol for the custom UIImageField like this:

protocol MyImageFieldProtocol: class {
    func imageTapped()
}

2) Then add a delegate like this:

weak var delegate: MyImageFieldProtocol?

3) Your UIViewController then conforms to the protocol like this:

class MyViewController: UIViewController, MyImageFieldProtocol {
}

4) Somewhere inside the view controller (viewDidLoad is usually a good place you assign the view controller to the image views delegate like this:

func viewDidLoad {
    super.viewDidLoad()
    myImageView.delegate = self
}

5) Then add the function to respond to the protocol action to the view controller like this:

func imageTapped {
    self.performSegue(withIdentifier: "MySegue", sender: nil)
}

Retain Cycle in ARC

A retain cycle is a situation when object A retains object B, and object B retains object A at the same time^*. Here is an example:

@class Child;
@interface Parent : NSObject {
    Child *child; // Instance variables are implicitly __strong
}
@end
@interface Child : NSObject {
    Parent *parent;
}
@end

You can fix a retain cycle in ARC by using __weak variables or weak properties for your "back links", i.e. links to direct or indirect parents in an object hierarchy:

@class Child;
@interface Parent : NSObject {
    Child *child;
}
@end
@interface Child : NSObject {
    __weak Parent *parent;
}
@end

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^* This is the most primitive form of a retain cycle; there may be a long chain of objects that retain each other in a circle.

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