In my AppDelegate's applicationDidFinishLaunching I need to create an object using data read from disk, and then pass this object to the initial view controller for display. What would be the best way to do this?
Right now I'm loading the storyboard programatically like so:
func applicationDidFinishLaunching(_ aNotification: Notification) {
importantThing = ImportantThing()
importantThing.load(url: URL(fileURLWithPath: "..."))
let storyboard = NSStoryboard(name: "Main", bundle: nil)
myWindowController = storyboard.instantiateController(withIdentifier: "MyWindowController") as! NSWindowController
(myWindowController.contentViewController as? MyViewController)?.importantThing = importantThing
myWindowController.showWindow(self)
}
But this feels clunky. For one, the property is being set after viewDidLoad, so now view setup is weird.
There must be a better way to do this. If possible, I would like to not resort to using a singleton, because I actually need to set up a few interconnected objects (two objects with important state that have references to each other, but it doesn't make sense for either to contain the other). What would be a good way to solve this?
What you're doing in the app delegate is correct. As for what you should do in the view controller, Apple's Master-Detail app template shows you the correct pattern (I've added a few comments):
// the interface
#IBOutlet weak var detailDescriptionLabel: UILabel!
// the property
var detailItem: NSDate? {
didSet {
self.configureView()
}
}
func configureView() {
// check _both_ the property _and_ the interface
if let detail = self.detailItem { // property set?
if let label = self.detailDescriptionLabel { // interface exists?
label.text = detail.description
}
}
}
override func viewDidLoad() {
super.viewDidLoad()
// at this point, its _certain_ that the interface exists
self.configureView()
}
If you think about it, you'll see that the interface is updated correctly regardless of the order of events — that is, regardless of whether viewDidLoad or the setting of the property comes first. Just follow that pattern.
Related
I have issues with using protocols to send data back to previous controller. I have studied SO questions and guides, but for some reason my data doesn't get transferred back.
In my second class I create data, that is later being sent back to first class:
protocol ImageEditorDelegate {
func sendImage(image: UIImage, id: String)
}
class PhotoEditorViewController: UIViewController {
var delegate: ImageEditorDelegate?
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func didPressSave(_ sender: UIButton) {
delegate?.sendImage(image: finalImage, id: imageThatWasSelected)
self.dismiss(animated: true, completion: nil)
}
}
And in my receiving class I have:
class NewProductViewController: UIViewController, ImageEditorDelegate {
var imageEditor: PhotoEditorViewController?
override func viewDidLoad() {
super.viewDidLoad()
imageEditor?.delegate = self
}
func sendImage(image: UIImage, id: String) {
print("Receiving images", image, id)
switch id {
case "1":
selectedImages[1] = image
productImage1.image = image
case "2":
selectedImages[2] = image
productImage2.image = image
case "3":
selectedImages[3] = image
productImage3.image = image
default:
break
}
}
}
But nothing happens, this func never gets called. I think my delegate is nil, or so, but how could I fix this issue? I have Also, I'm using VIPER as architecture with slightly customized segues, may this be the issue? I have tried simple segues, but had same issue.
I understand that this is rather simple question, but I couldn't understand what I doing wrong after I have read articles about protocols.
Thanks for your help!
What you're doing is very wrong. You have two view controllers with property references to one another:
class PhotoEditorViewController: UIViewController {
var delegate: ImageEditorDelegate?
}
class NewProductViewController: UIViewController, ImageEditorDelegate {
var imageEditor: PhotoEditorViewController?
}
Those are not weak references, so if you ever do get this to work — that is, if you ever arrange things so that the NewProductViewController's imageEditor is a PhotoEditorViewController whose delegate is that NewProductViewController — you will have a nasty retain cycle and a memory leak.
This suggests that you have not understood the protocol-and-delegate pattern. Only the presented view controller should have a delegate property pointing back to the presenter, and it should be weak. The presenter does not need any property pointing to the presented view controller, because it presents it.
you need to instantiate your photoEditor, like
photoEditor = PhotoEditorViewController()
before attempting to set its delegate.
you dont' have to do this next part, but I'd suggest making the delegate variable a weak variable to avoid any retain issues, like so
weak var delegate: ImageEditorDelegate?
and you'll need to mark the protocol as class like so
protocol ImageEditorDelegate : class {
I know that our IBOutlets should be private, but for example if I have IBOutlets in TableViewCell, how should I access them from another ViewController? Here is the example why I'm asking this kind of question:
class BookTableViewCell: UITableViewCell {
#IBOutlet weak private var bookTitle: UILabel!
}
if I assign to the IBOutlet that it should be private, I got an error in another ViewController while I'm accessing the cell property: 'bookTitle' is inaccessible due to 'private' protection level
If I understand your question correctly, you are supposing the #IBOutlet properties should be marked as private all the time... Well it's not true. But also accessing the properties directly is not safe at all. You see the ViewControllers, TableViewCells and these objects use Implicit unwrapping on optional IBOutlets for reason... You don't need to init ViewController when using storyboards or just when using them somewhere in code... The other way - just imagine you are creating VC programmatically and you are passing all the labels to the initializer... It would blow your head... Instead of this, you come with this in storyboard:
#IBOutlet var myLabel: UILabel!
this is cool, you don't need to have that on init, it will just be there waiting to be set somewhere before accessing it's value... Interface builder will handle for you the initialization just before ViewDidLoad, so the label won't be nil after that time... again before AwakeFromNib method goes in the UITableViewCell subclass, when you would try to access your bookTitle label property, it would crash since it would be nil... This is the tricky part about why this should be private... Otherwise when you know that the VC is 100% on the scene allocated there's no need to be shy and make everything private...
When you for example work in prepare(for segue:) method, you SHOULD NEVER ACCESS THE #IBOutlets. Since they are not allocated and even if they were, they would get overwritten by some internal calls in push/present/ whatever functions...
Okay that's cool.. so what to do now?
When using UITableViewCell subclass, you can safely access the IBOutlets (ONLY IF YOU USE STORYBOARD AND THE CELL IS WITHIN YOUR TABLEVIEW❗️)
and change their values... you see
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// We shouldn't return just some constructor with UITableViewCell, but who cares for this purposes...
guard let cell = tableView.dequeueReusableCell(withIdentifier: "bookTableViewCell", for: indexPath) else { return UITableViewCell() }
cell.bookTitle.text = "any given text" // This should work ok because of interface builder...
}
The above case should work in MVC pattern, not MVVM or other patterns where you don't use storyboards with tableViewControllers and embed cells too much... (because of registering cells, but that's other article...)
I will give you few pointers, how you can setup the values in the cell/ViewController without touching the actual values and make this safe... Also good practice (safety) is to make the IBOutlets optional to be 100% Safe, but it's not necessary and honestly it would be strange approach to this problem:
ViewControllers:
class SomeVC: UIViewController {
// This solution should be effective when those labels could be marked weak too...
// Always access weak variables NOT DIRECTLY but with safe unwrap...
#IBOutlet var titleLabel: UILabel?
#IBOutlet var subtitleLabel: UILabel?
var myCustomTitle: String?
var myCustomSubtitle: String?
func setup(with dataSource: SomeVCDataSource ) {
guard let titleLabel = titleLabel, let subtitleLabel = subtitleLabel else { return }
// Now the values are safely unwrapped and nothing can crash...
titleLabel.text = dataSource.title
subtitleLabel.text = dataSource.subtitle
}
// WHen using prepare for segue, use this:
override func viewDidLoad() {
super.viewDidLoad()
titleLabel.text = myCustomTitle
subtitleLabel.text = myCustomSubtitle
}
}
struct SomeVCDataSource {
var title: String
var subtitle: String
}
The next problem could be this:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
guard let destinationVC = segue.destination as? SomeVC else { return }
let datasource = SomeVCDataSource(title: "Foo", subtitle: "Bar")
// This sets up cool labels... but the labels are Nil before the segue occurs and even after that, so the guard in setup(with dataSource:) will fail and return...
destinationVC.setup(with: datasource)
// So instead of this you should set the properties myCustomTitle and myCustomSubtitle to values you want and then in viewDidLoad set the values
destinationVC.myCustomTitle = "Foo"
destinationVC.myCustomSubtitle = "Bar"
}
You see, you don' need to set your IBOutlets to private since you never know how you will use them If you need any more examples or something is not clear to you, ask as you want... Wish you happy coding and deep learning!
You should expose only what you need.
For example you can set and get only the text property in the cell.
class BookTableViewCell: UITableViewCell {
#IBOutlet weak private var bookTitleLabel: UILabel!
var bookTitle: String? {
set {
bookTitleLabel.text = newValue
}
get {
return bookTitleLabel.text
}
}
}
And then, wherever you need:
cell.bookTitle = "It"
Now outer objects do not have access to bookTitleLabel but are able to change it's text content.
What i usually do is configure method which receives data object and privately sets all it's outlets features.
I haven't come across making IBOutlets private to be common, for cells at least. If you want to do so, provide a configure method within your cell that is not private, which you can pass values to, that you want to assign to your outlets. The function within your cell could look like this:
func configure(with bookTitle: String) {
bookTitle.text = bookTitle
}
EDIT: Such a function can be useful for the future, when you change your cell and add new outlets. You can then add parameters to your configure function to handle those. You will get compiler errors everywhere, where you use that function, which allows you to setup your cell correctly wherever you use it. That is helpful in a big project that reuses cells in different places.
I am trying to build an NSCollectionView filled with multiple editable TextViews. (OS X app in Swift.) My subclass of NSCollectionViewItem is called NoteViewItem. I am trying to have the program detect when one of the TextView has changed. I tried using both controlTextDidChange and textDidChange in the NoteViewItem's delegate with test print statement to see which would work. ControlTextDidChange did nothing; textDidChange recognized a change happened, so I went with that.
The problem is that textDidChange appears to point to a different NoteViewItem than the one that was shown on screen in the first place. It wasn't able to recognize the variable (called theNote) set in the original NoteViewItem; when I ask NoteViewItem to print String(self), I get two different results, one while setting the initial text and one in textDidChange. I'm wondering if I've set up my delegates and outlets wrongly. Any thoughts on why my references are off here?
Here's my code for NoteViewItem:
import Cocoa
class NoteViewItem: NSCollectionViewItem, NSTextViewDelegate
{
// MARK: Variables
#IBOutlet weak var theLabel: NSTextField!
#IBOutlet var theTextView: NSTextView!
var theNote: Note?
{
didSet
{
// Pre: The NoteViewItem's theNote property is set.
// Post: This observer has set the content of the *item's text view*, and label if it has one.
guard viewLoaded else { return }
if let theNote = theNote
{
// textField?.stringValue = theNote.noteText
theLabel.stringValue = theNote.filename
theTextView.string = theNote.noteText
theTextView.display()
print("theTextView.string set to "+theTextView.string!+" in NoteViewItem "+String(self))
}
else
{
theLabel.stringValue = "Empty note?"
}
}
}
// MARK: Functions
override func viewDidLoad() {
super.viewDidLoad()
// Do view setup here.
// Hopefully this will set the note's background to white.
view.wantsLayer = true
view.layer?.backgroundColor = NSColor.whiteColor().CGColor
}
// MARK: - NSTextViewDelegate
/*
override func controlTextDidChange(notification: NSNotification)
{
print("Control text changed.")
}
*/
func textDidChange(notification: NSNotification)
{
if let noteyMcNoteface = theNote
{
print("On edit, we have a note: "+String(noteyMcNoteface))
}
else
{
print("On edit, we have no note. I am NoteViewItem "+String(self))
}
}
}
I figured it out. My delegate, in the TextView, was connected to the wrong object in the Interface Builder for NoteViewItem.xib. I had connected it to the object labelled Note View Item, under objects in the outline. It should have been connected to File's Owner instead, since File's Owner stands for the NoteViewItem.swift class associated with the xib.
You'd think that if you want to connect the delegate to the NoteViewItem class and there is exactly one Note View Item listed in the outline, then that Note View Item is the thing you want to connect it to. Nope, you connect it to something entirely different that isn't called the Note View Item but is the Note View Item. I'm glad Interface Builder makes things so simple.
I am working on a project with Swift and Storyboards. It's a conversion project from a traditional IB and Objective-C project. I am having an issue with a UITableView instantiating when the view is loaded. Let me explain.
The project is a navigation project. Here is an overview of the Storyboard.
The Storyboard's first viewController is HomeViewController and is a landing page that displays general info. The next VC is called FeedViewController shows a number of RSS feeds. You can see an expanded screen shot of the NavigationController, HomeViewController and FeedViewController in the picture below.
My problem is that I can't get the tableView to Instantiate. I first checked to make sure that my tableView was connected as an outlet and that the dataSource and delegate properties were connected. You can see this in the pic below.
In my FeedViewController class I have an Outler property called feedsTableView. You can see the declaration in the code below.
class FeedViewController: UIViewController, UITableViewDataSource, UITableViewDelegate, FLODataHandlerDelegate
{
// View Contoller and Protocol Properties
var floView : FLOViewController?
var dataHandler : FLODataHandler?
// Interface and Content Properties
var refreshControl : UIRefreshControl?
// IBOutlets
#IBOutlet weak var feedsTableView: UITableView!
#IBOutlet weak var backgroundImage: UIImageView!
In the HomeViewController I have a FeedViewController property that I intend to use to gain access to FeedViewController's feedsTableView.
class HomeViewController: UIViewController, FLODataHandlerDelegate, MFMailComposeViewControllerDelegate
{
// View Contoller and Protocol Properties
var feedViewController : FeedViewController?
var dataHandler : FLODataHandler?
When HomeViewController's viewDidLoad() method is called I start the dataHandler - which instantiates the FeedViewController - and set it to my FeedViewController property.
override func viewDidLoad()
{
super.viewDidLoad()
// Set up the gesture recognizer to allow for swiping to the feed VC.
let recognizer = UISwipeGestureRecognizer(target: self, action: Selector("goToNext"))
recognizer.direction = UISwipeGestureRecognizerDirection.Left
self.view.addGestureRecognizer(recognizer)
// Start the data handler
self.setUpDataHandler()
}
setUpDataHandler()
func setUpDataHandler()
{
// Intitalize FeedVC for use later in the VC
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let vc = storyboard.instantiateViewControllerWithIdentifier("FeedViewController") as! FeedViewController
self.feedViewController = vc
}
I also have a fail safe that if someone were to go to the FeedViewController before the setUpDataHandler() method is called then I instantiate FeedViewController here as well.
func goToNext()
{
// Grab the feedViewController so it can be pushed onto the stack. Make sure you set up the storyboard identifier.
let feedVC = self.storyboard!.instantiateViewControllerWithIdentifier("FeedViewController") as! FeedViewController
self.feedViewController = feedVC
self.navigationController!.pushViewController(self.feedViewController!, animated: true)
}
However the feedsTableView is not getting instantiated. In the viewDidLoad() method of FeedViewController I attempt to add the feedsTableView to a UIRefreshController.
override func viewDidLoad()
{
super.viewDidLoad()
self.refreshControl = UIRefreshControl()
self.refreshControl!.addTarget(self, action: "refreshInvoked:state:", forControlEvents: UIControlEvents.ValueChanged)
// See the note in viewDidLoad in FLOViewController.
self.feedsTableView.addSubview(self.refreshControl!)
}
When the app runs I get the following error.
fatal error: unexpectedly found nil while unwrapping an Optional value
The image below shows were this is called. It's the viewDidLoad() of the FeedViewController. As you can see in the picture I even tried instantiating the feedsTableView before adding it to the UIRefreshController and I still get the error.
Any help would be greatly appreciated.
Take care,
Jon
The reason why it doesn't work in the very last case, where you manually instantiate UITableView and assign that to self.feedsTableView, is that self.feedsTableView is declared weak. Thus, the table view comes into existence, is assigned, and vanishes in a puff of smoke because it has no memory management. By the time you get to the last line, self.feedsTableView is nil once again.
Thus, the solution for that last case is to remove the weak designation from your feedsTableView declaration.
That will get you past the crash in that last case. But of course you won't see anything because you are not also inserting the table view into your interface.
I know that this has to be a simple fix, but can't seem to understand why my code is not working. Basically I am trying to send a value from a text field in 1 view to a 2nd view's label.
ViewController.swift
#IBOutlet var Text1st: UITextField
#IBAction func Goto2ndView(sender: AnyObject) {
let view2 = self.storyboard.instantiateViewControllerWithIdentifier("view2") as MyView2
//view2.Label2nd.text=text;
self.navigationController.pushViewController(view2, animated: true)
}
MyView2.swift
#IBOutlet var Label2nd: UILabel
override func viewDidLoad() {
super.viewDidLoad()
var VC = ViewController()
var string = (VC.Text1st.text) //it doesn't like this, I get a 'Can't unwrap Option.. error'
println(string)
}
-------EDITED UPDATED CODE FROM (drewag)-------
ViewController.swift
let text = "text"
var sendString = Text1st.text
println(sendString) //successfully print it out.
let view2 = self.storyboard.instantiateViewControllerWithIdentifier("view2") as MyView2
view2.Label2nd.text=sendString;
self.navigationController.pushViewController(view2, animated: true)
MyView2.swift
#IBOutlet var Label2nd: UILabel
override func viewDidLoad() {
super.viewDidLoad()
var VC = ViewController()
var string = self.Label2nd.text
println(string) //still getting the error of an unwrap optional.none
}
var VC = ViewController() creates a new instance of ViewController. Unless there is a default value, you are not going to get any value out of VC.Text1st.text. You really should use a string variable on your second view controller to pass the data to it.
Also, a note on common formatting:
Class names should start with a capital letter (as you have)
Method / function names should start with a lower case letter
UIViewController subclasses should have "Controller" included in their name, otherwise, it looks like it is a subclass of UIView which is an entirely different level of Model View Controller (the architecture of all UIKit and Cocoa frameworks)
Edit:
Here is some example code:
class ViewController1 : UIViewController {
...
func goToSecondView() {
var viewController = ViewController2()
viewController.myString = "Some String"
self.navigationController.pushViewController(viewController, animated: true)
}
}
class ViewController2 : UIViewController {
var myString : String?
func methodToUseMyString() {
if let string = self.myString {
println(string)
}
}
...
}
Note, I am not creating ViewController2 using a storyboard. I personally prefer avoiding storyboards because they don't scale well and I find editing them to be very cumbersome. You can of course change it to create the view controller out of the storyboard if you prefer.
jatoben is correct that you want to use optional binding. IBOutlets are automatically optionals so you should check the textfield to see if it is nil.
if let textField = VC.Text1st {
println(textField.text)
}
This should prevent your app from crashing, but it will not print out anything because your text field has not yet been initialized.
Edit:
If you want to have a reference to your initial ViewController inside your second you're going to have to change a few things. First add a property on your second viewcontroller that will be for the first view controller:
#IBOutlet var Label2nd: UILabel //existing code
var firstVC: ViewController? //new
Then after you create view2, set it's firstVC as the ViewController you are currently in:
let view2 = self.storyboard.instantiateViewControllerWithIdentifier("view2") as MyView2 //already in your code
view2.firstVC = self //new
Finally in your viewDidLoad in your second view controller, use firstVC instead of the ViewController you recreated. It will look something like this:
override func viewDidLoad() {
super.viewDidLoad()
if let textField = firstVC?.Text2nd {
println(textField.text)
}
}
Use optional binding to unwrap the property:
if let string = VC.Text1st.text {
println(string)
}