I made a subclass of UILabel called UIScoreLabel, which is more specialized for my need of displaying a score. Here is the code:
class UIScoreLabel: UILabel
{
var scoreBackingInt: Int!
var score: Int {
get
{
return scoreBackingInt
}
set(newScore)
{
scoreBackingInt = newScore
self.text = NSString(format: "%0\(digits)d", newScore)
}
}
let digits: Int! // number of digits to display (for 0-padding)
init(digits: Int)
{
super.init()
self.digits = digits
self.score = 0
}
}
score is supposed to be a computed variable. Anyway, everything is fine when I instantiate a UIScoreLabel, but when I attempt to access any of the subclass' properties in any way (i.e. score), the compiler tells me 'UILabel' does not have a member named 'score'
Here is the line that gives me an error, in my ViewController:
creditsLabel.score = self.score
What gives?
You need to let the compiler know the class type. As you can see in the error message the compiler currently thinks the class is UILable so you need to update the class type (or cast the class type if you can't).
UILabel is a subclass of UIView and UIView's default initializer is init(frame: CGRect). This is the initializer that you need to use when you call super.
super.init(frame: CGRectZero)
self.digits = digits
self.score = 0
Also UILabel adopts NSCoding and has a required init that you need to implement. Since you are not using storyboards, you can just add the following to get rid of the compiler error:
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
Related
I'm trying to make my app more accessible for Voice Over users. I have a slider that has numbers 1-100. If a user with Voice Over turned on swipes up or down to change the value, several numbers are being skipped. This means that an exact number is not able to be set. I'm following the suggestion from this site on subclassing UISlider and overriding accessibilityIncrement() and accessibilityDecrement() but they do not get called when the slider value changes. Below is my subclassed slider. Any idea why the methods are not getting called?
class FontSizeSlider: UISlider {
required init?(coder: NSCoder) {
super.init(coder: coder)
self.isAccessibilityElement = true
self.accessibilityTraits.insert(.adjustable)
}
override init(frame: CGRect) {
super.init(frame: frame)
}
override func accessibilityIncrement() {
self.value += 1
self.sendActions(for: .valueChanged)
}
override func accessibilityDecrement() {
self.value -= 1
self.sendActions(for: .valueChanged)
}
}
This is something I need to know for work, so this was a fantastic exercise for me. Thank you for posting the question. Anyway, I got it to work after taking a peek at this page on Apple's website.
I could not get the increment/decrement methods to be called, either. I suspect they're stepper-specific. The value property, OTOH, gets called.
Here's the code I came up with to get it to work:
class FontSizeSlider: UISlider {
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
func setup() {
isAccessibilityElement = true
accessibilityLabel = "Font Size Slider"
accessibilityIdentifier = "fontSizeSlider"
// accessibilityIdentifier = AccessibilityConstants.fontSizeSlider.rawValue
minimumValue = 0
maximumValue = 100
isContinuous = true
}
override var accessibilityValue: String? {
get {
return sliderValueString
}
set {
super.accessibilityValue = sliderValueString
}
}
override var accessibilityTraits: UIAccessibilityTraits {
get {
return .adjustable
}
set {
super.accessibilityTraits = newValue
}
}
// Nobody needs to know about this outside the class, so marked it private
private var sliderValueString: String {
let stringValue = String(Int(value))
return "The font size is \(stringValue)"
}
}
You'll notice I used the setup() method, which does the same stuff for both initializers. You can tweak your values as you see fit for the min/max values.
You'll note I added accessibilityLabel, so it doesn't read off that it's a generic slider. I added the accessibilityIdentifier in there, too. That's something that can be used for UI tests so the element can be identified.
You'll probably want to put the accessibilityIdentifier somewhere where "everyone" can see it. Perhaps an enum. Here's what the enum implementation would look like:
enum AccessibilityConstants: String {
case fontSizeSlider
}
// Usage
accessibilityIdentifier = AccessibilityConstants.fontSizeSlider.rawValue
I overrode the accessibilityValue with a custom setter and getter. Additionally, I created a computed var for the string that's read off when the accessibilityValue is updated. Here's the code for that portion of it. Note I made it private because nobody outside the class needs to know about it:
// I adapted this from Apple's accessibility page that I posted above
override var accessibilityValue: String? {
get {
return sliderValueString
}
set {
super.accessibilityValue = sliderValueString
}
}
private var sliderValueString: String {
let stringValue = String(Int(value))
return "The font size is \(stringValue)"
}
One last thing...you don't need self everywhere unless you're accessing a property of your custom UISlider inside a closure like an animation block or a completion block.
Update
Deleted...
Update 2
So let's say you're on your viewController, you could add a target action to the slider, like so:
slider.addTarget(self, action: #selector(doSomething), for: .valueChanged)
#objc func doSomething() {
print("How much wood could a wood chuck chuck if a wood chuck could chuck wood")
}
Whenever value changes, your selector will get called.
I am new to Swift.
Currently I have made serval xib files and they can be rendered in the following codes
let mySubview:customView = customView(frame: CGRect(x:10,y:300, width: 312, height:355))
self.view.addSubview(mySubview)
"customView" is the custom view (.xib) file while there are many others. However, I want to render it with a function parameter. I have used string but I got an error for this:
func addComp(name:String){
let className = NSClassFromString("MyApp."+name) as! UIView.Type
let subview = className.init()
subview.frame = CGRect(x:10,y:300, width: 312, height:355)
self.view.addSubview(subview)
}
It says
"Fatal error: Unexpectedly found nil while unwrapping an Optional value"
Anyway, is there any ways to define a custom view with function parameters? Either with string or any other methods.
I'd say you're coming at this wrong. Don't turn a string to a type; use a type directly.
Here's a UIView subclass with a factory method that does everything your addComp does:
class MyFactoryView : UIView {
required override init(frame:CGRect) {
super.init(frame:frame)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder:aDecoder)
}
static func make(andAddTo v:UIView) {
let subv = self.init(frame:CGRect(x:10,y:300, width: 312, height:355))
v.addSubview(subv)
}
}
Okay, so let's say we have some subclasses of that type:
class MyView1 : MyFactoryView {}
class MyView2 : MyFactoryView {}
So now there's no need for any string. To enact our little drama, we just talk directly to the type; for example:
MyView1.make(andAddTo:self.view)
Here is some code from a project that, as you see it here, worked fine in Swift 2.3. Having now upgraded the project to Swift 3.0, this is producing an infinite loop at self.init().
class MyView: UIView
{
fileprivate let foo: String
required init? ( coder aDecoder: NSCoder )
{
fatalError( "init( NSCoder ) has not been implemented" )
}
convenience init ()
{
self.init()
foo = "bar"
}
}
I am told this should have infinite looped in Swift 2.3 too. Fair enough, I believe it, all I am able to tell you is that it didn't, but I don't know why. The possible solutions suggested in this post - Initializing swift class in objective c project causes infinite loop - are not useful because:
the convenience init() method in question really is a convenience
init;
self.init( frame: ) produces the buildtime error message
Incorrect argument label in call (have 'frame:', expected 'coder:'), and;
I have no instance of NSCoder to pass into self.init( coder: )
The convenience init should always delegate the initialization to a designated initializer for the superclass, in this case the UIView. Unfortunately the only solution I found is to do this:
class MyView: UIView {
fileprivate let foo: String = "bar"
convenience init() {
self.init(frame: .zero)
}
override init(frame: CGRect) {
super.init(frame: frame)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
}
This is what I have decided to do instead:
override init ( frame: CGRect )
{
foo = "bar"
super.init( frame: frame )
}
I am not happy with this solution as it means passing in a useless frame that I have to override later with constraints. If anyone has a better solution please do suggest it. Thank you.
UPDATE
Thanks to #Luca-D'Alberti for providing the above "correct" answer.
I have a baseclass:
class ViewController: UIViewController
{
init(nibName nibNameOrNil: String?)
{
super.init(nibName: nibNameOrNil, bundle: nil)
}
required init?(coder aDecoder: NSCoder) { }
}
a subclass:
class OneViewController: ViewController
{
private var one: One
init(one: One)
{
self.one = one
super.init(nibName: "OneNib")
}
required init?(coder aDecoder: NSCoder) { }
}
and a subclass of the above subclass:
class TwoViewController: OneViewController
{
private var two: Two
init(two: Two)
{
self.two = two
super.init(nibName: "TwoNib") <== ERROR
}
required init?(coder aDecoder: NSCoder) { }
}
At the indicated line I get the error:
Ambiguous reference to member 'init(one:)'
I don't understand why the compiler can't figure out I'm referring to ViewController's init(), like it managed to do in One's init().
What am I missing and/or doing wrong?
I don't understand why the compiler can't figure out I'm referring to ViewController's init(), like it managed to do in One's init()
It is because, from inside TwoViewController, the compiler can't see ViewController's init. The rule is:
As soon as you implement a designated initializer, you block inheritance of initializers.
Therefore, OneViewController has only one initializer, namely init(one:). Therefore, that is the only super initializer that TwoViewController can call.
If you want ViewController's init(nibName:) to be present in OneViewController, you must implement it in OneViewController (even if all it does is to call super).
The chapter in the Swift manual on Designated Initializers will clarify it, but basically OneViewController has only one way to set self.one, and that's by initialising using init(one: One). You cannot bypass that, which is what you are trying to do.
If what you were trying to do could succeed, what value would two.one have in the following?
let two = Two(two: SomeTwo)
print(two.one)
Answer - undefined. That's why it isn't allowed.
Having declared One.init(one:) it is now the Designated Initializer, and there's no way to go round it.
you don't necessary pass value into constructor's ViewController . you can define public object in oneViewController and you access of outer .
class OneViewController: ViewController {
public var one: One
}
let vc = storyboard?.instantiateViewControllerWithIdentifier("OneViewController") as OneViewController
let one = One()
vc.one = one
Looking at the a lecture slide in the Stanford iOS 9 course here, he is creating a new UIView with two initializers (one if the UIView was created from storyboard, and one if it was created in code). The following code is written at the bottom of that particular slide:
func setup() {....} //This contains the initialization code for the newly created UIView
override init(frame: CGRect) { //Initializer if the UIView was created using code.
super.init(frame: frame)
setup()
}
required init(coder aDecoder: NSCoder) { //Initializer if UIView was created in storyboard
super.init(coder:aDecoder)
setup()
}
The rule is that you must initialize ALL of your own properties FIRST before you can grab an init from a superclass. So why is it that in this case he calls his superclass init super.init BEFORE he initializes himself setup()? Doesn't that contradict the following rule:
Safety check 1 A designated initializer must ensure that all of the properties introduced by its class are initialized before it delegates up to a superclass initializer.
As mentioned above, the memory for an object is only considered fully initialized once the initial state of all of its stored properties is known. In order for this rule to be satisfied, a designated initializer must make sure that all its own properties are initialized before it hands off up the chain.
I haven't seen all the rest of the code in this example, but the rule is only that your properties have to be initialized (i.e. the memory they occupy has to be set to some initial value) before calling super.init(), not that you can't run extra setup code.
You can even get away with sort of not-really-initializing your properties by either declaring your properties lazy var, or using var optionals which automatically initialize to nil. You can then set them after your call to super.init().
For example:
class Foo: UIView {
var someSubview: UIView! // initializes automatically to nil
lazy var initialBackgroundColor: UIColor? = {
return self.someSubview.backgroundColor
}()
init() {
super.init(frame: .zero)
setup() // do some other stuff
}
func setup() {
someSubview = UIView()
someSubview.backgroundColor = UIColor.whiteColor()
addSubview(someSubview)
}
}