Global Variables vs Direct Conection to pass data between view controllers ios - ios

I don't think the title uses the right terminology so I'll try to clarify now.
I have two view controllers which i want to pass data between. view 1 has a tableView and the 2nd view has a MKMapView. Now in the corresponding controllers I want when you click on a cell in view 1 it sends you to the place on the map which the cell indicates eg. a New York cell would send to a map of new York. So I tried in the didSelectRowAtIndexPath that I create an instance of the second controller which would transfer the data to it. But when I did that it would always return a nil value in the second view controller.
So instead I created a 3rd swift file which has some global variables and when I transfer the data via them it works perfectly. Why is this so?
Cheers.
EDIT: Before the I went via a third file
Code for the ViewController 1
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
var selectedCell = array[indexPath.row]
var viewController2 = ViewController2()
viewController2.textLabel1 = selectedCell.name
coord.textLabel2 = selectedCell.coordinate
}
Code for ViewController 2
#IBOutlet weak var textLabel1: UILabel!
#IBOutlet weak var textLabel2: UILabel!
Code for View Controller 2 going via 3rd file
#IBOutlet weak var textLabel1: UILabel!
#IBOutlet weak var textLabel2: UILabel!
override func viewDidLoad() {
textLabel1.text = globalVar1
textLabel2.text = globalVar2
}
Code from the 3rd File
var globalVar1: String!
var globalVar2: String!
So from the comments below I take it that in the first way the textLabels hadn't been initialised yet, so the values I assigned to them where turned into nil values. Is this correct? If so how would you do the first way correctly

If I had to guess, and I would because I cannot comment for more info yet(i get in trouble ).
It's because you are trying to assign it to an outlet.
The outlet has not been set yet which means when it is set (I think around ViewDidLoad)
the outlet will be set to nil.
The properties should however be retained if the object hasn't gone out of the heap that is.

PSedu code:
first view :
Your table view
Second View:
your map view
How to work
In you second view:
Add a NSMutableArray *valueArraytoGet in .h file,set its property
#synchronize it in .m file
Now in your first view at didSelectRowAtIndex method
create object of Second View Controller
and assign data as
SecondViewController *object=......
object.valueArraytoGet=[assign ur value array here]....
Hope it will help

Related

Using UIColorPickerViewController to change the color of cell background color always returns black

I'm developing an app for my school that helps students better understand their grades by getting an analysis on their portfolio of assignments for each class. Right now I am at the point of letting the user create the classes they are in and customize the information within it that is displayed in a tableview with custom cells. The user gives the majority of the information in a child view where they input information such as class name, teacher, grade weighting, etc. I wanted to give the user the ability to change the color of the cell once they are viewing the TableView with all the cells - classes - they made. I decided to go about this by having the cells have a UIButton that they can click on for their determined cell to then pull up a UIColorPickerViewController.
What I wanted to happen was...
User taps button in cell
UIPickerViewController is pulled up
User selects their desired color
User exits UIPickerViewController
Cell is changed to the color
What is actually happening is this
User taps button in cell
Cell background becomes black right as UIPickerViewController is presented
User selects their desired color
User exits UIPickerViewController
Cell remains black
I used a delegate to send the information from the cells and then I used the "colorPickerViewControllerDidFinish()" function and it's still not working out. When I did some debugging I found that the value of the UIColorPickerViewController is actually being stored in the variable I am using, but only after I have already assigned it's value to the cell background so I'm unsure what to do. As you can probably tell, I'm new to swift so apologies for any stupid mistakes in my code.
Custom Cell File
// Protocol for VC's to conform to so they can distinguish which cell has a button being tapped
protocol newlyCreatedCellDelegate: AnyObject
{
func didTapButton(title: String, cellView: UIView)
}
class newlyCreatedClass: UITableViewCell {
// Telling the delegate what to do once they are assigned
weak var delegate: newlyCreatedCellDelegate?
#IBOutlet weak var classContentView: UIView!
#IBOutlet weak var classUIView: UIView!
#IBOutlet weak var classNameLabel: UILabel!
#IBOutlet weak var classTeacherNameLabel: UILabel!
#IBOutlet weak var pointType1NameLabel: UILabel!
#IBOutlet weak var pointType2NameLabel: UILabel!
#IBOutlet weak var pointType3NameLabel: UILabel!
#IBOutlet weak var percent1Label: UILabel!
#IBOutlet weak var percent2Label: UILabel!
#IBOutlet weak var percent3Label: UILabel!
#IBOutlet weak var colorButton: UIButton!
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
colorButton.layer.cornerRadius = 21
}
override func setSelected(_ selected: Bool, animated: Bool) {
super.setSelected(selected, animated: animated)
// Configure the view for the selected state
}
// Essentially creating the prep list for the delegate. If they are called - whoever it is - they will go through this 'checklist'
#IBAction func colorButtonTapped(_ sender: Any)
{
delegate?.didTapButton(title: classNameLabel.text!, cellView: classUIView)
}
}
ViewController Extensions
extension ClassSelection: newlyCreatedCellDelegate
{
func didTapButton(title: String, cellView: UIView)
{
let colorPickerVC = UIColorPickerViewController()
colorPickerVC.delegate = self
present(colorPickerVC, animated: true, completion: nil)
colorPickerViewControllerDidFinish(colorPickerVC)
// 'cellBackgroundColor' is a variable declared in the VC to transfer the UIColor value
cellView.backgroundColor = cellBackgroundColor
}
}
extension ClassSelection: UIColorPickerViewControllerDelegate
{
func colorPickerViewControllerDidFinish(_ viewController: UIColorPickerViewController) {
cellBackgroundColor = viewController.selectedColor
}
}
You should implement one more UIColorPickerViewControllerDelegate method:
func colorPickerViewControllerDidSelectColor(_ viewController: UIColorPickerViewController) {
cellBackgroundColor = viewController.selectedColor
}
It's a great start! As a really direct answer to your original question:
The reason for your problem is that in your didTapButton function you are presenting the color picker, but then immediately telling the app that the user is done with the picker, and then immediately setting the background color to cellBackgroundColor, which I assume has a default value of UIColor.black.
Instead you should delete those last 2 lines in your didTapButton function - just initialize the picker, set the delegate, and present the picker. Then the delegate method you chose - colorPickerViewControllerDidFinish isn't really the correct one for your purpose. Instead consider using the didSelect delegate method (see docs). When that method is called it will pass you the color the user selected, which you can simply use to set your background color and refresh your tableView cell if needed.
Since you mention you are a new Swift dev I will also mention that UITableView reuses its cells, so simply setting the background color of a cell once will not have the result you are expecting. You will see that as you scroll the cells up and down the colors will change in the various cells, so ultimately you'll need to store the color selections in another way so that each time a cell is being dequeued you can set the correct color based on user input. That part is outside of the scope of the original question, but just letting you know.

Access to ViewController outlet from TableViewController loaded at same time

I was reading the thread: IBOutlet of another view controller is nil
I have a problem very similar to that.
RequestViewController
class DenunciasResueltasViewController: UIViewController {
#IBOutlet var mapView: GMSMapView!
var solicitudes = [SolicitudesModel]()
var tempMap: GMSMapView!
override func viewDidLoad() {
super.viewDidLoad()
let camera = GMSCameraPosition.camera(withLatitude: 3.4824182, longitude: -8.1776567, zoom: 15)
self.mapView.camera = camera
}
func recenterMap(latitude:Float!, longitude:Float!) -> Void {
let coordinates = CLLocationCoordinate2DMake(CLLocationDegrees(latitude), CLLocationDegrees(longitude))
mapView = tempMap
self.mapView.animate(toLocation: coordinates)
}
RequestTableViewController
class RequestTableViewController: UITableViewController {
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
//Some code to fill the table
let viewController = self.storyboard?.instantiateViewController(withIdentifier: "RequestVC") as! RequestViewController
viewController.recenterMap(latitude: solicitudes[indexPath.row].getLatitude(), longitude: solicitudes[indexPath.row].getLongitude() )
return cell
}
}
Both components are initialized at same time in runtime, I mean, both are part of the same View.
And when the users click in a 'row' I wanna update the mapView
for that resason, I'm using the method 'RecenterMap'
But, the variable 'self.mapView' is always 'nil'.
How I can update this value?
You should use the delegate method didSelectRowAtIndexPath to do the recentering, because this is called when the user tapps on a cell. It could be that the Outlets of the first viewcontroller haven't yet been set when the second starts to fill its cells.
This is a common problem, wanting to access properties of a currently offscreen vc before you are going to present it.
You can solve it by forcing the view hierarchy to be build by accessing its view:
let _ = viewController.view
After this you are free to access any view-related property on the viewcontroller. So you should put it before you call .recenterMap
It's not really clear what are you trying to do: your code seem to instantiate a view controller with map for each table cell, but you don't actually present it after being instantiated.
You instantiate the RequestViewController, but it doesn't appear in the view hierarchy, thus the IBOutlet properties are not instantiated at that moment when you call them. Usually calling a view on a UIViewController instantiates all the outlets on it.
Alternatively, you could call self.present(requestViewController) in order for it to be presented.
What i understood is that, you have both the RequestViewController and RequestTableViewController, both are subview of a parent View,
1- your center on map function needs to be called on the delegate method :
didSelectRowAtIndexPath:
2- You need a reference to the RequestViewController and DO NOT INSTANTIATE IT FROM THE STORYBOARD. as you will get a new instance and not the one that is displayed already.

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().

ios Swift ViewController Loaded from Selecting TableView Cell Loses Reference

Full code for this branch here
View controller "MovieDetailsVC" is presented to the navigation controller when a cell is selected.
The presenting view controller, "ViewController", stores the row of the tableView to display in NSUserDefaults as an Int.
"MovieDetailsVC" reads the row ok. It then pulls the whole array of custom class info from CoreData and stores the array row in a property.
The data is displayed ok at first. The IBOutlet connections are setup ok. I've disconnected and reconnected twice all outlets on MovieDetailsVC, so that should be ok.
"viewDidLoad" is called a successive time. Not sure from where. When it is called, the coredata entity and row number are pulled ok.
The issue is at line "lblTitle.text = self.movieRecord.title". I'm assuming any of the IBOutlets would cause the same issue.
The error thrown is what you would see if the outlets were not connected:
fatal error: unexpectedly fond nil while unwrapping Optional value.
code for the MovieDetailsVC is below. Any ideas why this outlet link would break after working ok would be greatly appreciated.
import UIKit
import CoreData
class MovieDetailsVC: UIViewController {
#IBOutlet var lblTitle: UILabel!
#IBOutlet var lblDescr: UILabel!
#IBOutlet var lblLink: UILabel!
#IBOutlet var imgMovie: UIImageView!
var movieRecord:FavMovie!
var favMovies = [FavMovie]()
override func viewDidLoad() {
super.viewDidLoad()
fetchAndSetResult()
}
func fetchAndSetResult() {
let app = UIApplication.sharedApplication().delegate as! AppDelegate
let context = app.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: "FavMovie")
do {
let results = try context.executeFetchRequest(fetchRequest)
self.favMovies = results as! [FavMovie]
} catch let err as NSError {
print(err.description)
}
if let row = NSUserDefaults.standardUserDefaults().objectForKey("movieRow") as? Int {
self.movieRecord = self.favMovies[row]
configureCellDescr()
}
}
func configureCellDescr() {
lblTitle.text = self.movieRecord.title
lblDescr.text = self.movieRecord.descrWhyGood
lblLink.text = self.movieRecord.linkImdb
imgMovie.image = self.movieRecord.getImg()
}
}
I just have a look at your source code in github and find the problem. There are two issues and I will explain it following.
it does that the second time that the app overrides viewdidload
The reason that your code would call the viewDidLoad method twice is because you have a segue in your storyboard that connect the tableViewCell to movieDetailVC. This will present the movieDetailVC once you click the cell.
And in your code for didSelectCell method, you create another movieDetailVC object and present it.
So actually movieDetailVC would be presented twice when you click the cell. This cause the issue.
Any ideas why this outlet link would break after working ok would be greatly appreciated
The reason why the IBOutlet is nil is because of the way you present movieDetailVC in your code. You create the movieDetailVC object using: let movieDetailsVC = MovieDetailsVC(). Doing it this way, the IBOutlets will not be connected correctly, because ios dont know about the storyboard information.
The correct way to create a MovieDetailVC object is to instantiate from storyboard. See this post for difference.
Solution
There is a very simple solution for your code design:
just remove let movieDetailsVC = MovieDetailsVC() and self.navigationController?.presentViewController(movieDetailsVC, animated: true, completion: nil) from your ViewController class. Since you save the selection data in NSUserDefault, the cell segue will present movieDetailVC and your movieDetailVC can also get the selection data from userDefault.

passing data from UItableviewController to UItableViewcell

I cannot understand why some values are well passed from the tableViewController to my custom UITableViewCell, and some others are not.
In my UItableviewController.cellForRowAtIndexPath i set up a cell with some values, before returning this cell :
cell.label1.text = myCustomObject.id
cell.label2.text = myCustomObject.path
cell.myCustomObjectCellMember = myCustomObject
cell.pathCellMember = myCustomObject.path
return cell
On the custom UITableViewCell side, in awakeFromNib method, the two first cell members are Ok, the two last ones contain nil.
The only difference between the two first cell members and the two last ones is that the two first are declared as IBOutlet and linked to the storyboard, while the two others are not linked to the UI. But yet, it should be OK to write in these vars from the tableViewController, right ?
Here are the declarations of these variables in the custom UITableViewCell:
#IBOutlet weak var label1: UILabel!
#IBOutlet weak var label2: UILabel!
var pathCellMember : String!
var myCustomObjectCellMember: MyCustomObjectCellMember!
When logged (inside UITableViewCell.awakeFromNib), label1.text and label2.text show the correct value,
but pathCellMember and myCustomObjectCellMember display nil instead of the value assigned in UItableviewController.cellForRowAtIndexPath.
As requested, a more explicit code :
class CustomCellTableViewCell: UITableViewCell {
#IBOutlet weak var label1: UILabel!
#IBOutlet weak var label2: UILabel!
var pathCellMember : String!
var myCustomObjectCellMember: MyCustomObjectCellMember!
override func awakeFromNib() {
super.awakeFromNib()
println("label1 : \(self.label1.text!)") //displays the value assigned
println("label2 : \(self.label2.text!)") //displays the value assigned
println("pathCellMember: \(self.pathCellMember!)") //displays nil
println("myCustomObjectCellMember.path : \(self.myCustomObjectCellMember.path)") //displays `nil`
}
Thank you
In cellForRowAtIndexPath is where you will reuse (deque) each cell. This is where you need to assign your vars values to each cell. While awake does set the initial values they will only fire the first time before the cell is reused. Assign everything in cellForRow or willDisplayCell (background colors, etc).
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UITableView_Class/
Discussion
For performance reasons, a table view’s data source should generally reuse UITableViewCell objects when it assigns cells to rows in its tableView:cellForRowAtIndexPath: method. A table view maintains a queue or list of UITableViewCell objects that the data source has marked for reuse. Call this method from your data source object when asked to provide a new cell for the table view. This method dequeues an existing cell if one is available or creates a new one using the class or nib file you previously registered. If no cell is available for reuse and you did not register a class or nib file, this method returns nil.
If you registered a class for the specified identifier and a new cell must be created, this method initializes the cell by calling its initWithStyle:reuseIdentifier: method. For nib-based cells, this method loads the cell object from the provided nib file. If an existing cell was available for reuse, this method calls the cell’s prepareForReuse method instead.

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