Strong references and UIView memory issues - ios

I'm dealing with some deallocation issue and perhaps strong or circular referencing that can't figure out. I have three UIViews instantiating like below:
There is one main ViewController which I have added a UIView inside it in storyboard and the UIView has a weak outlet inside the class like:
class ViewController : UIViewController {
//MARK: - outlets
#IBOutlet weak var firstView: FirstUiview!
}
second UIView is added as a subview to the first view programmatically like:
class FirstUiview : UIView {
//creating an instance of secondUiView
lazy var mySecondView: SecondViewClass = {
let dv = SecondViewClass()
dv.backgroundColor = UIColor.red
return dv
}()
//sometime later by clicking on a button
self.addSubview(mySecondView)
//a button will be tapped to remove mySecondView;
//later will be called at some point upon tapping:
func removingSecondViewByTapping() {
if mySecondView.isDescendant(of: self) {
mySecondView.removeFromSuperview()
}
}
}
Now the SecondViewClass is :
class SecondViewClass : UIView {
//in this class I create bunch of uiview objects like below:
lazy var aView : UIView = {
let hl = UIView()
hl.tag = 0
hl.backgroundColor = UIColor.lightGray
return hl
}()
self.addSubview(aView) //... this goes on and I add other similar views the same way.
//creating an instance of thirdView
var let thirdView = UIView()
self.addSubview(thirdView)
}
Now if user taps the button to remove mySecondView and then add it again at some other time (still in the same ViewController) I expect all the subviews of mySecondView to have been released and gone but they are all there. I would appreciate it a lot if someone can point it to me where am I keeping a strong reference or if there is a circular referencing issue? or perhaps something else?

You have two strong references to your views, your custom property and the view hierarchy reference established when you call addSubview. When you remove the view from the view hierarchy, your class, itself, still has its strong reference to it.
You could solve this by making your reference optional, and when you call removeFromSuperview, also manually set your reference to nil. Or, perhaps easier, you might resolve this by using weak references, letting the view hierarchy maintain the strong references for you. And because your custom property is weak, when you remove it from the view hierarchy (thus eliminating the only strong reference to it), your weak reference will automatically become nil:
class FirstView: UIView {
weak var secondView: SecondView? // note the `weak` reference, which is obviously an optional
//sometime later by clicking on a button
func doSomething() {
let subview = SecondView()
subview.backgroundColor = .red
self.addSubview(subview)
secondView = subview
}
// a button will be tapped to remove secondView;
// later will be called at some point upon tapping ...
func removingSecondViewByTapping() {
secondView?.removeFromSuperview()
}
}

Related

Update subviews of UIView from ViewController

I have a UIViewController that implements a custom UIView, so;
override func loadView() {
view = CustomView()
}
The custom view has a few lables and buttons and all the normal stuff, problem is in my viewController I have a request, and when that request is done, I'd like to update some of those lables/buttons.
Right now, in my CustomView, I have functions, such as;
func updateView() {
labelOne.isHidden = true
LabelTwo.isHidden = false
}
So I call the appropriate function from my viewController when the request is done.
This works, but it feels wrong, is there a neater way to update the subviews of my custom UIView, from my viewController? Should I maybe be using protocols or delegates?
One thing I've found quite neat in the past is passing the model directly to the custom view, then using didSet to trigger updates.
class CustomView: UIView {
let labelOne = UILabel()
let labelTwo = UILabel()
var object:CustomObject! {
didSet {
self.labelOne.text = object.name
self.labelTwo.text = object.description
}
}
...
}
This means in your UIViewController you can do the request and then pass the model straight to the custom view.
RequestHelper.getObject() { object in
self.customView.object = object
}
Obviously here I'm guessing at your request and object names but hopefully you get the idea.

How to set the delegate of a subview

I have a custom view created by subclassing UIView, and it has two UITextView subviews which are instantiated inside its init method. Let's say for clarifying things, that I have a superview A containing two UITextViews B and C.
On the other hand, I have the UIViewController VC that manages the superview A, and its responsible of its control. This means that it has the method that controls what happens when the user changes text on C.
When someone has to control a UITextView, he usually does something like
textView.delegate = self
I want to do the same, but C is not visible from VC. VC just uses A, so I have
a.delegate = self
and then I have come with the idea of doing this inside the implementation of A:
weak var delegate: UITextViewDelegate? {
get {
return c.delegate
}
set {
c.delegate = newValue
}
}
But this is giving me an error, saying that it's unwrapping an optional value whose actual value is nil.
So, what's the correct way of controlling UITextView C (that is inside UIView A) from VC, which only has an instance of A.
It is most probably that c maybe nil. To solve this, you need to set the delegate after c is initialised.
Alternatively, create your own delegate - ADelegate! This way you can name your own delegate methods with more meaningful names!
protocol ADelegate : class {
func cDidChange()
}
In A:
weak var delegate: ADelegate?
Now A should implement UITextViewDelegate, set c.delegate to self, and relay the methods to self.delegate.
If you have added the UITextField's in the Xcode Interface Builder, you can create outlets for the textfields in your ViewController (even when the textfields are sub-sub-children of the view, that the viewcontroller controls).
Thus continuing with your naming, you add the following outlets to your ViewController:
#IBOutlet weak var B: UITextField!
#IBOutlet weak var C: UITextField!
and in your ViewController's viewDidLoad() add:
B.delegate = self
C.delegate = self
If you created the UITextField's programmatically you can set their tag value to e.g. 1 and 2(0 is most likely already used) and then get the view from your ViewController like this:
let B = self.view.viewWithTag(1) as? UITextField
let C = self.view.viewWithTag(2) as? UITextField
Of course, make sure that the ViewController extends UITextFieldDelegate, that is:
class ViewController: UIViewController, UITextFieldDelegate {...}

Swift 2.2 - Updating UILabel throws "unexpectedly found nil while unwrapping an optional value"

I am new to iOS development so forgive me if I'm missing something obvious. I have a view controller that contains a subview in which I've created a numpad, and for the time being I want to give the numpad view its own UIView subclass because I want to do a few different things with it. Right now the numpad is just creating a string from the keys that get pressed, and I've set up a delegate to pass that string anywhere else I want to use it (though I've also tried accessing the raw input directly in the view controller with let a = subview(); label.text = a.rawInput).
Whenever I try to set the text of the UILabel in the view controller to the subview's raw input, whether by delegation or directly, the UILabel is found to be nil and throws the error in the title.
Things I've tried:
Setting the text inside a viewDidLoad override, and outside of it
Setting a variable (testInput) inside the view controller to adopt the subview's raw input and setting the label text to that (I've confirmed that the variable inside the view controller gets properly set, so no delegation issues)
Using didSet on the testInput variable both to set label text to testInput and to try calling viewDidLoad and set the label text in there (printing testInput inside this didSet does print the right string, FWIW)
Deleting and relinking the IBOutlet for my label
Strong and weak storage for the IBOutlet variable
Trying to do the same thing in another subview within the view controller, in case for some reason it was the view controller's own fault
Searching everywhere for a solution that works
I'm stumped. Here is my relevant numpad code:
import UIKit
protocol NumpadDelegate {
func updateInput(input: String)
}
class Numpad: UIView {
// MARK: UI outlets
#IBOutlet weak var decButton: UIButton!
// MARK: Properties
var rawInput: String = ""
var visibleInput: String = ""
var calcInput: String = ""
var operandReady = 1
var percentWatcher = 0
var delegate: NumpadDelegate? = BudgetViewController()
// MARK: Functions
func handleRawInput(str: String) {
rawInput += str
print("numpad input is \(rawInput)")
delegate?.updateInput(rawInput)
}
And here is the view controller code:
import UIKit
class BudgetViewController: UIViewController, NumpadDelegate {
// MARK: Properties
//#IBOutlet weak var transactionValueField: UITextField!
#IBOutlet weak var remainingCashForIntervalLabel: UILabel!
#IBOutlet weak var intervalDenoterLabel: UILabel!
#IBOutlet weak var currencyDenoterLabel: UILabel!
#IBOutlet weak var mainDisplayView: TransactionType!
#IBOutlet weak var inactiveInputView: InactiveInput!
#IBOutlet weak var numpadView: Numpad!
#IBOutlet weak var rawInputLabel: UILabel!
var remainingCashForInterval = 40
let display = TransactionType()
var testInput = "" {
didSet {
viewDidLoad()
}
}
override func viewDidLoad() {
super.viewDidLoad()
// let numpad = Numpad()
// numpad.delegate = self
// print("\(numpad.delegate)")
self.rawInputLabel.text = testInput
}
func updateInput(input: String) {
print("view controller now has \(input)")
display.mainInput = input
testInput = input
}
As a side note, in case you noticed that my protocol isn't a class type, for some reason adding : class to it and declaring my delegate as a weak variable prevents the delegation from working. Any suggestions there?
You assigned the delegate like so:
var delegate: NumpadDelegate? = BudgetViewController()
That doesn't reference the view controller whose scene was presented, but rather a new blank one. And that's why when you used weak, why it was deallocated (because that orphaned instance of the view controller has no strong references to it).
You should define the protocol to be a class protocol again, and define delegate to be:
weak var delegate: NumpadDelegate?
And then, in the view controller's viewDidLoad, uncomment the line that sets that delegate:
numpadView.delegate = self
But, do not uncomment the line that says numpad = Numpad(); that is incorrect as that creates yet another Numpad instance. But you do want to set the delegate of the existing Numpad, though.
Both of these issues (namely, getting a reference to the view controller that is to be the delegate of the Numpad view; and getting a reference to the Numpad view that the storyboard presented) suggest some misunderstanding about the the process of presenting a storyboard scene.
The process is basically as follows:
the view controller is instantiated, using whatever class you specified as the base class for that scene;
its root view, as well as all of the subviews on that scene will be instantiated for you;
the storyboard will hook up the IBOutlet references in the scene's base class to the outlets you created; and
the view controller's viewDidLoad is called.
That's an oversimplification, but that's the basic process.
But the key is that all of these view controllers and views that are referenced on the storyboard scene are created for you. You don't want to try to create any of these yourself (and the presence of the () at the end of BudgetViewController() or Numpad() says "create a new instance of x", which is not what we want to do here).
So, when we need to get a reference to the view controller so that we can programmatically specify the delegate for one of the views, you can do this in viewDidLoad, at which point self references the view controller that the storyboard instantiated for us. We don't want to instantiate a new one. Likewise, when you want to reference the Numpad that the storyboard instantiated for us (in order to hook up its delegate), you use the IBOutlet you hooked up in Interface Builder, rather than programmatically instantiate a new Numpad with Numpad().

Strongly referenced variable may cause memory issues

I have been programming in Swift for a couple months now. Recently, I have focused more on concepts of how Swift as a language works.
Hence, recently while reading apple documentation on Automatic Reference Counting(ARC), I came across the following lines:
This one on top:
In most cases, this means that memory management “just works” in Swift, and you do not need to think about memory management yourself. ARC automatically frees up the memory used by class instances when those instances are no longer needed.
And in the next paragraph, the following:
To make this possible, whenever you assign a class instance to a property, constant, or variable, that property, constant, or variable makes a strong reference to the instance. The reference is called a “strong“ reference because it keeps a firm hold on that instance, and does not allow it to be deallocated for as long as that strong reference remains.
I am a little confused as to what is the dynamics of the situation. I have noted while using storyboards, that you set reference to weak, hence the class looks like this, also what I would call case 1:
Case 1
class SomeClass : UIViewController {
#IBOutlet weak var nameLabel : UILabel!
override func viewDidLoad() {
nameLabel.text = "something."
}
}
Here, the label has one-to-one weak reference with the ViewController, and as soon as the Controller is changed, reference is broken (memory dealloc) since it is weak. Hence, no issues related to the memory.
Pardon me if the above statement is wrong or loosely held. I would be glad if someone confirms my assumption or counters it.
My question is about the second case however, where I do not use storyboards and class looks like below:
Case 2
class SomeClass : UIViewController {
var nameLabel : UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
override func viewDidLoad() {
view.addSubView(nameLabel)
// view.addConstraints...
}
}
For the above case, My assumption is that the ViewController has one-on-one strong reference with the label, and the view inside ViewController also has strong reference with the label.. If the class is changed/ label is removed from subview.. then I think the memory would not be deallocated. Or at least the view controller will maintain a strong reference to the label (as per the docs.)
I confirmed this by removing label from view's subviews and printing out the label (It gave me an instance of UILabel with frame that was at 0 origin and 0 size.) hence an instance that isn't nil.
The only thing I could gather from this was that although the label was removed from UIView, it still maintained a strong reference with the controller, hence permanent state in memory. Am I right?
If this is the case. How should I prevent my code from having such memory issues? The bigger problem is that if I declare my variable like so, I get a nil while adding it as a subview of main view in controller.
weak var nameLabel : UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
If declaring variables like in the second case can cause permanent strong references how should I declare them instead to not have memory issues?
So to conclude, my question is:
In cases where no storyboard outlets are used, and variables are strongly referenced to the view controller, will these references cause memory issues?
If so, what code declaration practice must I follow?
If not so, please provide thoughtful arguments with valid explanations to counter it.
Again, pardon me if I am incorrect anywhere.
Thank you in advance.
The only thing I could gather from this was that although the label was removed from UIView, it still maintained a strong reference with the controller, hence permanent state in memory. Am I right?
No. There's no big issue here.
The label has no strong reference to the view controller — if it did, that would be a retain cycle and would cause both the label and the view controller to leak. For this very reason, a view should never keep a strong reference to its view controller.
Here, however, it's the other way around: the view controller has a strong reference to the label. That's fine. It's true that the label therefore stays in existence after it has been removed from its superview. But that might not be bad. In many cases, it's good! For example, suppose you intend to put the label back into the interface later; you will need to have retained it.
If you are sure you won't need to keep the label around later, then simply use an Optional wrapping a UILabel as your instance property. That way, you can assign nil to the label instance property when you're done with it, and the label will go out of existence.
But in any case there is no leak here and you should just stop worrying. When the view controller goes out of existence, the label will go out of existence too. The label lived longer than it had to, but that's tiny and unimportant on the grand scale of things.
create the label when you need ,then call addsubView to make an strong reference to it and make an weak reference to your member var like this:
class ViewController: UIViewController {
weak var label : UILabel?
override func viewDidLoad() {
super.viewDidLoad()
let label = UILabel()
view.addSubview(label)
self.label = label
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
print(label)
//click first Optional(<UILabel: 0x7fb562c3f260; frame = (0 0; 0 0); userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fb562c11c70>>)
//click second nil
label?.removeFromSuperview()
}
}
anyway while the viewcontroller release ,the label will be release and view.subview will be release too.
Demo
i wrote an easy demo make the ViewControllerTest to be the rootviewcontroller
class Test{
weak var label:UILabel?
static let instance = Test()
}
class ViewControllerTest: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let item = UIBarButtonItem(title: "Test", style: .Plain, target: self, action: #selector(self.test))
self.navigationItem.rightBarButtonItem = item
}
func test(){
print(Test.instance.label)
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
let vc = ViewController()
self.navigationController?.pushViewController(vc, animated: true)
print(vc.nameLabel)
let test = Test.instance
test.label = vc.nameLabel
}
}
class ViewController: UIViewController {
var nameLabel : UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
return label
}()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor.whiteColor()
view.addSubview(nameLabel)
let item = UIBarButtonItem(title: "Test", style: .Plain, target: self, action: #selector(self.test))
self.navigationItem.rightBarButtonItem = item
}
func test(){
print(Test.instance.label)
}
}
I don't think strongly referenced variables to view controller cause any memory issues.
Normally views are deallocated before deallocating their view controller. For example, in in your code, when deallocating the view, ARC decreases the counter pointing to namelabel, so it passes from 2 to 1. Then, when deallocating the view controller it decreases the counter again, from 1 to 0. Once there are 0 references pointing to namelabel its removed.
A weak reference is a reference that does not keep a strong hold on
the instance it refers to, and so does not stop ARC from disposing of
the referenced instance. This behavior prevents the reference from
becoming part of a strong reference cycle. You indicate a weak
reference by placing the weak keyword before a property or variable
declaration
> Weak references must be declared as variables, to indicate that their
value can change at runtime. A weak reference cannot be declared as a
constant.
Because a weak reference does not keep a strong hold on the instance
it refers to, it is possible for that instance to be deallocated while
the weak reference is still referring to it. Therefore, ARC
automatically sets a weak reference to nil when the instance that it
refers to is deallocated. Because weak references need to allow nil as
their value, they always have an optional type. You can check for the
existence of a value in the weak reference, just like any other
optional value, and you will never end up with a reference to an
invalid instance that no longer exists
Source: Apple docs
A weak reference is just a pointer to an object that doesn't protect the object from being deallocated by ARC. While strong references increase the retain count of an object by 1, weak references do not. In addition, weak references zero out the pointer to your object when it successfully deallocates. This ensures that when you access a weak reference, it will either be a valid object, or nil.
Hope can help you to understand better a weak reference, be it related to a storyboard item or created programmatically.
I always explain it to my students like this.
With a strong reference, you can see a value, and you have a lasso around it. You have a say in whether the value remains alive.
With a weak reference, you can see it, but there's no lasso. You have no say in whether the value lives or not.
For your situation to avoid occurrence of Memory leak for a second. You can go with Matt answer.
For better understanding, create a custom UILabel class under MRC flag in build phases->Complie sources.
In custom class, override retain and release method. Put breakpoints on them.
Use that custom UILabel class in your view controller with ARC flag ON. Go with matt answer or use below optional declaration of UILabel.
import UIKit
class ViewController: UIViewController {
var label:UILabel? = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.text = "something"
return label
}()
override func viewDidLoad() {
super.viewDidLoad()
self.view.addSubview(self.label!)
//namelabel goes out of scope when method exists.
//self.view has 1+ ref of self.label
}
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
self.label?.removeFromSuperview()//-1 ref of self.label
self.label = nil
print(self.label)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
You will have clear picture of how ARC works and why weak ref of UILabel causes crash while adding to UIView.

Passing data between views in ONE ViewController in Swift

All of the searches I've done focus on passing data between view controllers. That's not really what I'm trying to do. I have a ViewController that has multiple Views in it. The ViewController has a slider which works fine:
var throttleSetting = Float()
#IBAction func changeThrottleSetting(sender: UISlider)
{
throttleSetting = sender.value
}
Then, in one of the Views contained in that same ViewController, I have a basic line that (for now) sets an initial value which is used later in the DrawRect portion of the code:
var RPMPointerAngle: CGFloat {
var angle: CGFloat = 2.0
return angle
}
What I want to do is have the slider's value from the ViewController be passed to the View contained in the ViewController to allow the drawRect to be dynamic.
Thanks for your help!
EDIT: Sorry, when I created this answer I was having ViewControllers in mind. A much easier way would be to create a method in SomeView and talk directly to it.
Example:
class MainViewController: UIViewController {
var view1: SomeView!
var view2: SomeView!
override func viewDidLoad() {
super.viewDidLoad()
// Create the views here
view1 = SomeView()
view2 = SomeView()
view.addSubview(view1)
view.addSubview(view2)
}
#IBAction func someAction(sender: UIButton) {
view1.changeString("blabla")
}
}
class SomeView: UIView {
var someString: String?
func changeString(someText: String) {
someString = someText
}
}
Delegate:
First you create a protocol:
protocol NameOfDelegate: class { // ": class" isn't mandatory, but it is when you want to set the delegate property to weak
func someFunction() // this function has to be implemented in your MainViewController so it can access the properties and other methods in there
}
In your Views you have to add:
class SomeView: UIView, NameOfDelegate {
// your code
func someFunction() {
// change your slider settings
}
}
And the last step, you'll have to add a property of the delegate, so you can "talk" to it. Personally I imagine this property to be a gate of some sort, between the two classes so they can talk to each other.
class MainViewController: UIViewController {
weak var delegate: NameOfDelegate?
#IBAction func button(sender: UIButton) {
if delegate != nil {
let someString = delegate.someFunction()
}
}
}
I used a button here just to show how you could use the delegate. Just replace it with your slider to change the properties of your Views
EDIT: One thing I forgot to mention is, you'll somehow need to assign SomeView as the delegate. But like I said, I don't know how you're creating the views etc so I can't help you with that.
In the MVC model views can't communicate directly with each other.
There is always a view controller who manages the views. The views are just like the controllers minions.
All communication goes via a view controller.
If you want to react to some view changing, you can setup an IBAction. In the method you can then change your other view to which you might have an IBOutlet.
So in your example you might have an IBAction for the slider changing it's value (as in your original question) from which you could set some public properties on the view you would like to change. If necessary you could also call setNeedsDisplay() on the target view to make it redraw itself.

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