Question: What Is Retain Count In Swift?

What is strong reference in Swift?

Strong Reference Cycle.

In essence, strong references are used to describe the relationship between objects.

When an object has a strong reference to another object, this creates a retain cycle that prevents the object that is being referenced from being deallocated and increases the retain count to 1..

Does copy increase retain count?

No, a copied object will have a retain count of 1, just like a newly initialized object. I highly recommend you read the Memory Management Guide if you wish to learn more. If you’re new to iOS development, the iOS App Programming Guide should be read first, and is a great use of your time.

What is retain in iOS?

You send an object a retain message when you want to prevent it from being deallocated until you have finished using it. An object is deallocated automatically when its reference count reaches 0 . retain messages increment the reference count, and release messages decrement it.

What is a retain cycle?

Retain Cycle is the condition when 2 objects keep a reference to each other and are retained, it creates a retain cycle since both objects try to retain each other, making it impossible to release. Example: A person lives in a department, a department has one person.

How do you find the retaining cycle in Swift?

1 Answer. If you are using Xcode 8 or above, you can use the memory graph thingy to see what object holds a reference to what object. Now you can clearly see that it is retained by a closure! That is how you use the memory graph to see where you should put weak-references and avoid retain cycles.

What is retain in Swift?

What are retain cycles and memory leaks? A memory leak in iOS is when an amount of allocated space in memory cannot be deallocated due to retain cycles. Since Swift uses Automatic Reference Counting (ARC), a retain cycle occurs when two or more objects hold strong references to each other.

What is weak in Swift?

A weak reference is just a pointer to an object that doesn’t protect the object from being deallocated by ARC. In Swift, all weak references are non-constant Optionals (think var vs. … let ) because the reference can and will be mutated to nil when there is no longer anything holding a strong reference to it.

What is lazy property in Swift?

Lazy Stored Properties. A lazy stored property is a property whose initial value isn’t calculated until the first time it’s used. … You must always declare a lazy property as a variable (with the var keyword), because its initial value might not be retrieved until after instance initialization completes.

What is memory management in iOS?

Memory management is the programming discipline of managing the life cycles of objects and freeing them when they are no longer needed. Managing object memory is a matter of performance; if an application doesn’t free unneeded objects, its memory footprint grows and performance suffers.

How do you debug a memory graph?

You can generate a memory graph of the objects and allocations in your app by clicking the Debug Memory Graph button in Xcode’s debug area at the bottom of the workspace window. The memory graph shows the memory regions your app is using and the size of each region.

Why is IBOutlet weak?

In Mac development an IBOutlet is usually a weak reference: if you have a subclass of NSViewController only the top-level view will be retained and when you dealloc the controller all its subviews and outlets are freed automatically. UiViewController use Key Value Coding to set the outlets using strong references.

How do I declare an IBOutlet in Swift?

Simplicity rules in swift. If you have a property defined that you want to make accessible to your storyboards, just add the @IBOutlet attribute before your property. Similarly with @IBAction to connect storyboard actions back to code. class MyViewController: UIViewController { @IBOutlet weak var likeButton: UIButton?

What is retain count?

Retain Count represents number of owners for a particular object. It is zero till object does not have any owners. Increase in one ownership claim will cause retain count to increase by 1 and decrease will cause it to decrement by 1. Example: – Class A object is created using alloc/init and retain count is 1.

Where is memory leak in iOS app?

Automatic memory leak detection on iOSOpen Xcode and build for profiling.Launch Instruments.Use the app, trying to reproduce as many scenarios and behaviors as possible.Watch for leaks/memory spikes.Hunt down the source of the memory leaks.Fix the problem.Apr 13, 2016

What is Property in iOS?

They define memory management, type, and access attributes of the values they store such as strong , weak , assign , readonly , readwrite , etc. Properties store values assigned to them in an instance variable that by convention has the same name as the property but starts with an underscore prefix.

What is strong attribute of property?

strong / retain : Declaring strong means that you want to “own” the object you are referencing. Any data that you assign to this property will not be destroyed as long as you or any other object points to it with a strong reference.

What is difference between weak and strong in Swift?

A strong reference means that you want to “own” the object you are referencing with this property/variable. In contrast, with a weak reference you signify that you don’t want to have control over the object’s lifetime. A weak reference is like observing the tree from afar. …

What is unowned in Swift?

Swift version: 5.2. Unowned variables are similar to weak variables in that they provide a way to reference data without having ownership. However, weak variables can become nil – they are effectively optional.

Why outlets are weak in Swift?

weak is used because in most situations the owner of the outlet isn’t the same as the owner of the view. For example, a view controller doesn’t own someLabel – the view controller’s view does. var because outlets are, by definition, set after initialization.

How do I stop retaining cycles in Swift?

We can solve this in two ways. First, we can use [unowned self]: Now the closure doesn’t have a strong reference anymore. Just be careful when using [unowned self] since that, if the object has already been deallocated when the closure is called, a crash will occur.

How do I use Xcode Instruments?

Launch Instruments from the Dock: Control-click the Xcode icon in the Dock, and then choose Options > Open Developer Tool > Instruments from the shortcut menu to launch Instruments. Add Instruments to Launchpad: Place an alias to the Instruments app in your /Applications folder to make it appear in Launchpad.