Providing my own initializer for UICollectionViewFlowLayout - ios

I'd like to provide my own initializer for my UICollectionViewFlowLayout subclass, for the purposes of calculating my itemSize property at runtime to scale my cells properly for different screen sizes. I understand that the simplest way to do so, is to adjust the default UICollectionViewFlowLayout from the UICollectionViewController like this:
//in UICollectionViewController
override func viewDidLoad() {
super.viewDidLoad()
let someWidth = ...
let someHeight = ...
let layout = collectionViewLayout as! UICollectionViewFlowLayout
layout.itemSize = CGSize(width: someWidth, height: someHeight)
}
However, I need to subclass UICollectionViewFlowLayout for the purposes of some custom layout for my UICollectionReusableView, so I thought it would be nice to declare the itemSize property in my layout subclass.
I am trying to make my own initializer, like so:
override init() {
super.init()
itemSize = CGSizeMake(someWidth, someHeight)
}
but I am greeted with the requirement:
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
When I attempt to load this viewController, I'm greeted with the fatalError. Next, I try to simply let the super implementation deal with it:
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
I recall various bits of information that is forcing my mind in a state of caution, something along the lines of: If one decides to subclassing something that requires the NSCoding things, one must do something to the variables that I added to the subclass.
Can anyone advise me on this?

-- EDIT --
Is this what you're looking for?
class HmIsThisOK: UICollectionViewFlowLayout {
var myCustomSize: CGSize = CGSizeMake(60.0, 23.5)
override var itemSize: CGSize {
get { return myCustomSize }
set { myCustomSize = newValue }
}
}
or does it just make sense to follow the usual protocol of initializing itemSize in your implementation of prepareForLayout()?
If none of that works for you, it's perfectly safe to do the required init junk and just add your code to the end of it after calling super.init(...). You're not concerned with tying your custom init to the coding/encoding process, which has to do from awakening from the Nib file (usually Main.storyboard). Because the two inits() are required, you usually factor out your custom init code into a helper method.
Finally, If you are indeed awakening this object from the Nib file, you can use an overridden awakeFromNib() function to do custom initialization, without worrying about the init() prickliness.

Related

When is "required init?(coder aDecoder: NSCoder)" called on a UIView or UIViewController?

When I create a subclass of UIView or UIViewController with a stored property, Xcode will not compile my project unless I include an implementation of required init?(coder aDecoder: NSCoder). Currently, I have the following implementation to shut the compiler up:
required init?(coder aDecoder: NSCoder) {
fatalError()
}
I understand why I'm required to include this initializer; my subclass needs to conform to the NSCoding protocol because its superclass conforms to it, and this initializer is part of the NSCoding protocol so it needs to work with my class, i.e. initialize all of my class's stored properties (which the superclass version of the initializer won't do).
I imagine that a correct implementation would look something like this:
class MyView: UIView {
let label: UILabel
override init(frame: CGRect) {
label = UILabel()
super.init(frame: frame)
}
required init?(coder aDecoder: NSCoder) {
if let label = aDecoder.decodeObject() as? UILabel {
self.label = label
} else {
return nil
}
super.init(coder: aDecoder)
}
override func encode(with aCoder: NSCoder) {
aCoder.encode(label)
super.encode(with: aCoder)
}
}
However, considering that my application has over 50 custom views and view controllers, correctly implementing this function in every custom view and view controller is a lot of work.
So, I'm wondering if it's necessary to implement this initializer correctly, or if I can just leave it throwing a fatal error. In other words, will this initializer ever be called if I don't call it in my own code? I think I read that it might be called by a Storyboard, but my app doesn't use any Storyboards.
This initialiser will be called if an instance of your view is used in a storyboard scene.
It is up to you whether to create a functioning initialiser or not, but it should mostly be a matter of copying code from init(frame:)
It provides an NSCoder instance as a parameter, which you need only if you are using iOS serialization APIs. This is not used often, so you can ignore it. If you are curious to learn, serialisation converts an object in a byte stream that you can save on disk or send over the network.
During the initalization of a view controller, you usually allocate the resources that the view controller will need during its lifetime. So, this include model objects or other auxiliary controllers, like network controllers.

init() inside custom cell class that is delegate and datasource of collectionView

Im really confused trying to init() some stuff inside my custom cell class that i want to be the datasource and delegate of a collectionview.
How do i init() so that i have the data in an array ready to be used by cellForItemAt??
var partArray : [CollectionStruct] = []
init(partArray: [CollectionStruct]) {
super.init(partArray: [CollectionStruct])
innerCollectionView.delegate = self
innerCollectionView.dataSource = self
//innerCollectionView.tag = item
// add some stuff from local sql lite to array
// this is how i normally do this in viewDidLoad
// but cant use that in cell subclass
BuildArray.buildArrayFromQuery(queryForCollection: "Part", delegateSender: "DownloadPack", completeBlock: { (result) in
if result.isEmpty == false {
self.partArray = result
}
})
}
If i just do:
init() {
// stuff for the array
}
I get swift suggesting i include this block:
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
You can't create your own initializers for the UITableViewCell. The only two initializers you can override are one that recieves a frame (init(frame)) and one that recieves a code (init(coder)).
In order to find a solution for your problem, you can a use either a property or a method in which recieves the data array. Either one would be called or set after the cell is created. You make your setup, and afterwards you call reloadData() of the collectionView.
If you decide to use a property, you could do this mentioned logic in the didSet of the property.

Custom UIView subclass with XIB in Swift

I'm using Swift and Xcode 6.4 for what it's worth.
So I have a view controller that will be containing some multiple pairs of UILabels and UIImageViews. I wanted to put the UILabel-UIImageView pair into a custom UIView, so I could simply reuse the same structure repeatedly within the aforementioned view controller. (I'm aware this could be translated into a UITableView, but for the sake of ~learning~ please bear with me). This is turning out to be a more convoluted process than I imagined it would be, I'm having trouble figuring out the "right" way to make this all work in IB.
Currently I've been floundering around with a UIView subclass and corresponding XIB, overriding init(frame:) and init(coder), loading the view from the nib and adding it as a subview. This is what I've seen/read around the internet so far. (This is approximately it: http://iphonedev.tv/blog/2014/12/15/create-an-ibdesignable-uiview-subclass-with-code-from-an-xib-file-in-xcode-6).
This gave me the problem of causing an infinite loop between init(coder) and loading the nib from the bundle. Strangely none of these articles or previous answers on stack overflow mention this!
Ok so I put a check in init(coder) to see if the subview had already been added. That "solved" that, seemingly. However I started running into an issue with my custom view outlets being nil by the time I try to assign values to them.
I made a didSet and added a breakpoint to take a look...they are definitely being set at one point, but by the time I try to, say, modify the textColor of a label, that label is nil.
I'm kind of tearing my hair out here.
Reusable components seem like software design 101, but I feel like Apple is conspiring against me. Should I be looking to use container VCs here? Should I just be nesting views and having a stupidly huge amount of outlets in my main VC? Why is this so convoluted? Why do everyone's examples NOT work for me?
Desired result (pretend the whole thing is the VC, the boxes are the custom uiviews I want):
Thanks for reading.
Following is my custom UIView subclass. In my main storyboard, I have UIViews with the subclass set as their class.
class StageCardView: UIView {
#IBOutlet weak private var stageLabel: UILabel! {
didSet {
NSLog("I will murder you %#", stageLabel)
}
}
#IBOutlet weak private var stageImage: UIImageView!
var stageName : String? {
didSet {
self.stageLabel.text = stageName
}
}
var imageName : String? {
didSet {
self.stageImage.image = UIImage(named: imageName!)
}
}
var textColor : UIColor? {
didSet {
self.stageLabel.textColor = textColor
}
}
var splatColor : UIColor? {
didSet {
let splatImage = UIImage(named: "backsplat")?.tintedImageWithColor(splatColor!)
self.backgroundColor = UIColor(patternImage: splatImage!)
}
}
// MARK: init
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
if self.subviews.count == 0 {
setup()
}
}
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
func setup() {
if let view = NSBundle.mainBundle().loadNibNamed("StageCardView", owner: self, options: nil).first as? StageCardView {
view.frame = bounds
view.autoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight
addSubview(view)
}
}
/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
override func drawRect(rect: CGRect) {
// Drawing code
}
*/
}
EDIT: Here's what I've been able to get so far...
XIB:
Result:
Problem: When trying to access label or image outlets, they are nil. When checking at breakpoint of said access, the label and image subviews are there and the view hierarchy is as expected.
I'm OK with doing this all in code if thats what it takes, but I'm not huge into doing Autolayout in code so I'd rather not if there's a way to avoid it!
EDIT/QUESTION SHIFT:
I figured out how to make the outlets stop being nil.
Inspiration from this SO answer: Loaded nib but the view outlet was not set - new to InterfaceBuilder except instead of assigning the view outlet I assigned the individual component outlets.
Now this was at the point where I was just flinging shit at a wall and seeing if it'd stick. Does anyone know why I had to do this? What sort of dark magic is this?
General advice on view re-use
You're right, re-usable and composable elements is software 101. Interface Builder is not very good at it.
Specifically, xibs and storyboard are great ways to define views by re-using views that are defined in code. But they are not very good for defining views that you yourself wish to re-use within xibs and storyboards. (It can be done, but it is an advanced exercise.)
So, here's a rule of thumb. If you are defining a view that you want to re-use from code, then define it however you wish. But if you are defining a view that you want to be able to re-use possibly from within a storyboard, then define that view in code.
So in your case, if you're trying to define a custom view which you want to re-use from a storyboard, I'd do it in code. If you are dead set on defining your view via a xib, then I'd define a view in code and in its initializer have it initialize your xib-defined view and configure that as a subview.
Advice in this case
Here's roughly how you'd define your view in code:
class StageCardView: UIView {
var stageLabel = UILabel(frame:CGRectZero)
var stageImage = UIImageView(frame:CGRectZero)
override init(frame:CGRect) {
super.init(frame:frame)
setup()
}
required init(coder aDecoder:NSCoder) {
super.init(coder:aDecoder)
setup()
}
private func setup() {
stageImage.image = UIImage(named:"backsplat")
self.addSubview(stageLabel)
self.addSubview(stageImage)
// configure the initial layout of your subviews here.
}
}
You can now instantiate this in code and or via a storyboard, although you won't get a live preview in Interface Builder as is.
And alternatively, here's roughly how you might define a re-usable view based fundamentally on a xib, by embedding the xib-defined view in a code-defined view:
class StageCardView: UIView {
var embeddedView:EmbeddedView!
override init(frame:CGRect) {
super.init(frame:frame)
setup()
}
required init(coder aDecoder:NSCoder) {
super.init(coder:aDecoder)
setup()
}
private func setup() {
self.embeddedView = NSBundle.mainBundle().loadNibNamed("EmbeddedView",owner:self,options:nil).lastObject as! UIView
self.addSubview(self.embeddedView)
self.embeddedView.frame = self.bounds
self.embeddedView.autoresizingMask = .FlexibleHeight | .FlexibleWidth
}
}
Now you can use the code-defined view from storyboards or from code, and it will load its nib-defined subview (and there's still no live preview in IB).
I was able to work it around but the solution is a little bit tricky. It's up to debate if the gain is worth an effort but here is how I implemented it purely in interface builder
First I defined a custom UIView subclass named P2View
#IBDesignable class P2View: UIView
{
#IBOutlet private weak var titleLabel: UILabel!
#IBOutlet private weak var iconView: UIImageView!
#IBInspectable var title: String? {
didSet {
if titleLabel != nil {
titleLabel.text = title
}
}
}
#IBInspectable var image: UIImage? {
didSet {
if iconView != nil {
iconView.image = image
}
}
}
override init(frame: CGRect)
{
super.init(frame: frame)
awakeFromNib()
}
required init?(coder aDecoder: NSCoder)
{
super.init(coder: aDecoder)
}
override func awakeFromNib()
{
super.awakeFromNib()
let bundle = Bundle(for: type(of: self))
guard let view = bundle.loadNibNamed("P2View", owner: self, options: nil)?.first as? UIView else {
return
}
view.translatesAutoresizingMaskIntoConstraints = false
addSubview(view)
let bindings = ["view": view]
let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat:"V:|-0-[view]-0-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: bindings)
let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat:"H:|-0-[view]-0-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: bindings)
addConstraints(verticalConstraints)
addConstraints(horizontalConstraints)
}
titleLabel.text = title
iconView.image = image
}
This is how it looks like in interface builder
This is how I embedded this custom view in the example view controller defined on a storyboard. Properties of P2View are set in the attributes inspector.
There are 3 points worth mentioning
First:
Use the Bundle(for: type(of: self)) when loading the nib. This is because the interface builder renders the designables in the separate process which main bundle is not the same as your main bundle.
Second:
#IBInspectable var title: String? {
didSet {
if titleLabel != nil {
titleLabel.text = title
}
}
}
When combining IBInspectables with IBOutlets you have to remember that the didSet functions are called before awakeFromNib method. Because of that, the outlets are not initialized and your app will probably crash at this point. Unfortunatelly you cannot omit the didSet function because the interface builder won't render your custom view so we have to leave this dirty if here.
Third:
titleLabel.text = title
iconView.image = image
We have to somehow initialize our controls. We were not able to do it when didSet function was called so we have to use the value stored in the IBInspectable properties and initialize them at the end of the awakeFromNib method.
This is how you can implement a custom view on a Xib, embed it on a storyboard, configure it on a storyboard, have it rendered and have a non-crashing app. It requires a hack, but it's possible.

How to initialize the different properties of Custom UITableViewCell in swift

I was trying to work with custom tableview cells for the tableview in my project. Right now I have got the tableview working using the custom cell class that I have created. I am using XIB for the cell.
But now the problem is that I want to add a gradient layer & an extra label as properties to my cell class and I want to get them initialize. I am writing the code for these properties in the init() like
override init(){
//Code to initialize the properties of cell
.....
super.init()
}
And I have also have the required init() which is like this
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
But its not working its just giving an error at required init().
I know how to get this done in Objective-C but have no idea how to do this in swift. Please give me some pointers on how to get this done.
EDIT : Yeah I did try initializing the properties in the awakeFromNib() where I got error saying I can't assign to property in self. And in init(coder:) also I was unable to initialize the properties.
Thanks in advance :)
Something wrong in your code. I create new project, create custom UITableViewCell via nib, and put such code, and it works fine:
override func awakeFromNib() {
super.awakeFromNib()
self.textLabel.text = "testing cells";
self.detailTextLabel?.text = "text";
}
Did you register cell's nib in table view?
self.tableView.registerNib(UINib(nibName: "TableViewCell", bundle: nil), forCellReuseIdentifier: "Cell");
Also did configure right the nib in Interface Builder? Does you change UITableViewCell class to your custom class?

Get property from NSCoder in required init(coder aDecoder: NSCoder)

I am implementing a Circle class (subclass of UIView) in Swift that sets its radius in its initializer according to the frame that is passed in init(frame: CGRect) like so:
override init(frame: CGRect)
{
radius = frame.width/2.0
super.init(frame: frame)
}
I also want to ensure for the case when the circle is instantiated from Interface Builder, so I also implement 'required init(coder aDecoder: NSCoder)` (which I am forced to do by Xcode anyway).
How can I retrieve the frame property of the view that is somehow contained in aDecoder. What I want to achieve basically would look like this:
required init(coder aDecoder: NSCoder)
{
var theFrame = aDecoder.someHowRetrieveTheFramePropertyOfTheView // how can I achieve this?
radius = theFrame.width/2.0
super.init(coder: aDecoder)
}
You could compute the radius after the frame has been set by super.init():
required init(coder aDecoder: NSCoder)
{
radius = 0 // Must be initialized before calling super.init()
super.init(coder: aDecoder)
radius = frame.width/2.0
}
Martin's answer is the correct one. (Voted). You might be able to find the way that the base class encodes the frame value and extract it, but that is fragile. (It relies on private details of the implementation of the base class, which might change and break your app in the future.) Don't develop code that depends on non-public implementation details of another class, or of your base class. That's a future bug just waiting to happen.
The pattern in initWithCoder is to first call super to get the values for the ancestor class, then extract the values for your custom class.
When you do it that way, the ancestor class will have already set up your view's frame for you, and you can just use that.

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