I have a feeling there is more than one problem with this code, but my first issue is that my delegate returns nil and I do not know why. First, is my delegate:
import UIKit
//delegate to move information to next screen
protocol userEnteredDataDelegate {
func userDidEnterInformation(info:NSArray)
}
Next, I have a var defined for the delegate and I believe the ? makes it an optional variable? This is defined inside the class
var dataPassDelegate:userEnteredDataDelegate? = nil
Now, after my user has entered information into the fields in the view, I want to add those field values to an array and then pass that array on to the next view where it will be added to. I have pieced this code together from some YouTube examples but I think I am missing a needed part. When do I assign some kind of value to the dataPassDelegate var so it is not nil when the if statement comes? Do I even need that if statement?
if blankData != 1 {
//add code to pass data to next veiw controller
enteredDataArray = [enterDate.text, enterSeason.text, enterSport.text, enterDispTo.text]
//println(enteredDataArray)
self.appIsWorking ()
if (dataPassDelegate != nil) {
let information: NSArray = enteredDataArray
println(information)
dataPassDelegate!.userDidEnterInformation(information)
self.navigationController?.popViewControllerAnimated(true)
} else {
println ("dataPassDelegate = nil")
}
//performSegueWithIdentifier("goToDispenseScreenTwo", sender: self)
activityIndicator.stopAnimating()
UIApplication.sharedApplication().endIgnoringInteractionEvents()
}
blankData = 0
}
Your help is appreciated.
A delegate is a pointer to another object that conforms to a particular protocol. Often you use delegates to refine the behavior of your class, or to send back status information o the results of an async network request
When you set your dataPassDelegate delegate is up to you.
What is the object that has the dataPassDelegate property? What object will be serving as the delegate?
You need to create 2 objects (the object that will be serving as the delegate, and the object that has the dataPassDelegate property) and link them up.
We can't tell you when to do that because we don't know what you're trying to do or where these objects will be used.
Related
Is there any way of passing data from 1st view controller to (say) 3rd view controller without passing the data through the 2nd view controller?
I actually have a final submit button on the 4th view controller which gathers all the data right from the 1st view controller.
I want the data of each view controller to be directly transferred to the 4th view controller where the submit button is, without going through the view controllers to reach there.
I have already tried passing data through view controllers think there can be a more clear way of directly transferring data specially images as these are the main part of my data.
You could use a "Model" for this purpose with a delegate pattern.
A model is a class (or struct) which can be accessible by several VCs.
The delegate is going to be used to "notify" that a property value has changed.
/// Should be implemented by your VC
protocol MyModelDelegate: AnyObject {
func dataToShareChanged(to data: dataToShare)
}
/// Use the same instance for the VC1 and VC4
final class MyModel {
weak var delegate: MyModelDelegate?
var dataToShare: Foo {
didSet { delegate?.dataToShareChanged(to: dataToShare) }
}
}
In your case by the 1th and the 4th. Each of those VC should have the same instance of the model. You can achive this by giving the model object to the VCs if you initialize them.
If you are working with storyboards, you have to assging the models in the "viewDidLoad" for instance.
So you VC would look like:
class MyController: UIViewController, MyModelDelegate {
var model: MyModel?
func viewDidLoad() {
...
model.delegate = self
}
// Implementation of the delegate function.
func dataToShareChanged(to data: dataToShare) {
/// assign the new data value here
}
}
If you use this approach, you would not need to pass data though the VCs at all. Simple assign the new value in the model and the other VC is going to receive those data changes through the model delegate function.
Passing data forward from one view controller to the next isn't necessarily a bad thing. However when dealing with large amounts of data especially images you can easily run into memory pressure via this method.
Delegate way looks promising if all you needed was to inform the current viewcontroller neighbour (forward or backward) about data change.
Let me suggest an alternative set of solutions.
First off, don't manage image objects in memory. If you don't need it for anything else, write it to your apps temporary directory, keep hold of the URL and let go of the UIImage object. The snippet below lets you save your UIImage object to NSTemporaryDirectory with a name and return a URL object.
func saveImageToTempDirectory(image: UIImage, withName: String) -> URL? {
let url = URL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true)
.appendingPathComponent(withName, isDirectory: false)
.appendingPathExtension("jpg")
// Then write to disk
if let data = image.jpegData(compressionQuality: 0.8) {
do {
try data.write(to: url)
return url
} catch {
//handle error
return nil
}
}
return nil
}
You can choose to pass the URL from this method from one view controller to the other. Have this method in a Util class for better organization.
Method 1
Write the image urls from specific viewcontrollers into some local storage. You could use UserDefaults for this as its the easiest. You could also create separate folders for each viewcontroller while saving temp directory.
Method 2
Singletons. While singletons are frowned upon since they always hold state and becomes hard to test and/or debug, you could make use of a Singleton class that holds all your local URLs as part of arrays.
final class ImagePathManager {
static let shared = ImagePathManager()
var firstViewControllerImages: [URL] = []
//Initializer access level change now
private init(){}
}
You can append urls from first viewcontroller to ImagePathManager.shared.firstViewControllerImages and access them the same way from anywhere else in your application.
That being said, Singleton pattern usage is a slippery slope and you should always be very careful while using it in your apps.
So, I am new to cloudKit and to working with multiple threads in general, which I think is the source of the problem here, so if I simply need to research more, please just comment so and I will take that to heart.
Here is my question:
I am working in Swift 3 Xcode 8.1
I have in my view controller this variable:
var contactsNearby: [String:CLLocation]?
Then at the end of ViewDidLoad I call one of my view controllers methods let's call it:
populateContactsNearby()
inside that method I call:
container.discoverAllIdentities(completionHandler: { (identities, error) in
for userIdentity in identities! {
self.container.publicCloudDatabase.fetch(withRecordID: userIdentity.userRecordID!, completionHandler: { (userRecord, error) in
let contactsLocation = userRecord?.object(forKey: "currentLocation")
if self.closeEnough(self.myLocation!, contactLocation: contactsLocation as! CLLocation) {
var contactsName = ""
contactsFirstName = userIdentity.nameComponents?.givenName
if contactsName != "" && contactsLocation != nil {
self.contactsNearby?["\(contactsName)"] = contactsLocation as? CLLocation
}
}
})
}
})
}
I apologize if I am missing or have an extra bracket somewhere. I have omitted some error checking code and so forth in order to get this down to bare-bones. So the goal of all that is to populate my contactsNearby Dictionary with data from CloudKit. A name as the key a location as the value. I want to use that data to populate a tableview. In the above code, the call to closeEnough is a call to another one of my view controllers methods to check if the contact from CloudKit has a location close enough to my user to be relevant to the apps purposes. Also myLocation is a variable that is populated before the segue. It holds the CLLocation of the app users current location.
The Problem:
The if statement:
if contactsName != "" && contactsLocation != nil { }
Appears to succeed. But my view controllers variable:
var contactsNearby: [String:CLLocation]?
Is never populated and I know there is data available in cloudKit.
If it's relevant here is some test code that I have in cellForRowAtIndexPath right now:
let contact = self.contactsNearby?.popFirst()
let name = contact?.key
if name != nil {
cell.textLabel?.text = name
}else {
cell.textLabel?.text = "nothing was there"
}
My rows alway populate with "nothing was there". I have seen answers where people have done CKQueries to update the UI, but in those answers, the user built the query themselves. That seems different from using a CloudKit function like discoverAllIdentities.
I have tried to be as specific as possible in asking this question. If this question could be improved please let me know. I think it's a question that could benefit the community.
Okay, I need to do some more testing, but I think I got it working. Thank you Paulw11 for your comment. It got me on the right track.
As it turns out there were 2 problems.
First, as pointed out I have an asynchronous call inside a for loop. As recommended, I used a dispatchGroup.
Inside the cloudKit call to discoverAllIdentities I declared a dispatchGroup, kind of like so:
var icloudDispatchGroup = DispatchGroup()
Then just inside the for loop that is going to make an async call, I enter the dispatchGroup:
icloudDispatchGroup.enter()
Then just before the end of the publicCloudDatabase.fetch completion handler I call:
icloudDispatchGroup.leave()
and
icloudDispatchGroup.wait()
Which, I believe, I'm still new to this remember, ends the dispatchGroup and causes the current thread to wait until that dispatchGroup finishes before allowing the current thread to continue.
The Above took care of the multithreading issue, but my contactsNearby[String:CLLocation]? Dictionary was still not being populated.
Which leads me to the 2nd problem
At the top of my view controller I declared my Dictionary:
var contactsNearby: [String: CLLocation]?
This declared a dictionary, but does not initialize it, which I don't think I fully realized, so when I attempted to populate it:
self.contactsNearby?["\(contactsName)"] = contactsLocation as? CLLocation
It quietly failed because it is optional and returned nil
So, in viewDidLoad before I even call populateContactsNearby I initialize the dictionary:
contactsNearby = [String:CLLocation]()
This does not make it cease to be an optional, which Swift being strongly typed would not allow, but merely initializes contactsNearby as an optional empty Dictionary.
At least, that is my understanding of what is going on. If anyone has a more elegant solution, I am always trying to improve.
In case you are wondering how I then update the UI, I do so with a property observer on the contactsNearby Dictionary. So the declaration of the dictionary at the top of the view controller looks like this:
var contactsNearby: [String: CLLocation]? {
didSet {
if (contactsNearby?.isEmpty)! || contactsNearby == nil {
return
}else{
DispatchQueue.main.sync {
self.nearbyTableView.reloadData()
}
}
}
}
I suppose I didn't really need to check for empty and nil. So then in cellForRowAtIndexPath I have something kind of like so:
let cell = tableview.dequeueReusableCell(withIdentifier: "nearbyCell", for: indexPath)
if contactsNearby?.isEmpty == false {
let contact = contactsNearby?.popFirst()
cell.textLabel?.text = contact?.key
}else {
cell.textLabel?.text = "Some Placeholder Text Here"
}
return cell
If anyone sees an error in my thinking or sees any of this heading for disaster, feel free to let me know. I still have a lot of testing to do, but I wanted to get back here and let you know what I have found.
I have a project with various class files. I have a barcode scanner which I have used from an online source which outputs the values in an alert controller. What I would like to do is take the barcode value and pass it back to a my main class and using a function parse it and display it in the relevant labels. For some reason I cannot get it to do this if anybody has any ideas that would be great. I have spent all day trying to figure this out without any luck.
barcodeScanner class relevant section
/* AVCaptureMetadataOutputObjectsDelegate */
func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {
if alertController != nil {
return
}
if metadataObjects != nil && metadataObjects.count > 0 {
if let machineReadableCode = metadataObjects[0] as? AVMetadataMachineReadableCodeObject {
// get the barcode string
let type = machineReadableCode.type
let barcode = machineReadableCode.stringValue
I need to get the barcode let value above to the passengerInformation class where it will be passed through submitCodeAuto function to write the labels.
passengerInformation().self.submitCodeAuto(barcode)
My crack at it above which doesn't seem to work..
// display the barcode in an alert
let title = "Barcode"
let message = "Type: \(type)\nBarcode: \(barcode)"
displayAlert(title, message: message)
}
}
}
}
passengerInformation class
#IBOutlet weak var firstNameResponse: UILabel!
#IBOutlet weak var lastNameResponse: UILabel!
#IBAction func submitCodeAuto(sender: AnyObject!) {
firstNameResponse.text = barcodeProtocol(barcode).firstName
lastNameResponse.text = barcodeProtocol(barcode).lastName
}
Above the submitCodeAuto function also sends the incoming barcode through another function called barcodeProtocol which formats it allowing for first and last name to be retrieved.
I have currently tested the labels with a button running a textfield value through barcodeProtocol and displaying in the labels so that all is working.
I have also hooked up a button to a new viewcontroller with the scanner class that works fine. Showing the camera scanning and displaying the value.
but I just haven't been able to join them up. The app is returning fatal error: unexpectedly found nil while unwrapping an Optional value
Any help would be great thanks.
In your function:
#IBAction func submitCodeAuto(sender: AnyObject!) {
firstNameResponse.text = barcodeProtocol(barcode).firstName
lastNameResponse.text = barcodeProtocol(barcode).lastName
}
where did you get 'barcode' from?
Try replacing it with
#IBAction func submitCodeAuto(sender: AnyObject!) {
firstNameResponse.text = barcodeProtocol(sender as! String).firstName
lastNameResponse.text = barcodeProtocol(sender as! String).lastName
}
I am assuming that your method barcodeProtocol takes in any string and perfectly parses it into firstname and lastname
Your code is riddled with problems.
You create a new instance of your passengerInformation class from your barcodeScanner code, invoke the submitCodeAuto() method, and then forget about the newly created passengerInformation object. (presumably it's a view controller.)
It does not make sense to create a new view controller, send it a message, and then forget about it. That won't do anything. You probably want to instantiate your custom passengerInformation view controller from a storyboard, set a barcode string property in the view controller, and then present it modally using presentViewController:animated:completion:. In your passengerInformation view controller's viewWillAppear method, you should take the barcode property, extract the info you need from it, and install it into your text fields.
Your submitCodeAuto() method is declared as an IBAction even though you're not using it that way. It takes a parameter sender which you ignore, and instead you use a variable barcode which you don't show.
Your submitCodeAuto() function should probably take a parameter barcode of type String, since that's what it seems to be doing.
You have several classes who's class names start with lower-case letters. Class names should start with upper-case letters.
I have set up my view controllers so that they send a notification once their -viewDidLoad method is about to return. For example:
class MyViewController: UIViewController{
override func viewDidLoad() {
super.viewDidLoad()
//Do Stuff
var notificationCenter = NSNotificationCenter.defaultCenter();
notificationCenter.postNotificationName("AViewControllerDidLoadNotification", object: self);
}
}
My AppDelegate class is listening for this notification and implementing the method shown in this picture.
In case the picture isn't loading, the method takes the notification sent by the view controllers as it's only argument and then tests whether the UIViewController's title property has a non-nil value. If the title property is non-nil it logs the title.
However, as you can see in the debugger panel, the title property of the view controller is nil and the if statement is still evaluating to true.
I am admittedly new to optional values. But I have recreated this situation in a swift playground and the if statement evaluates to false. Any ideas?
You've gotten yourself into rather an odd situation with your very peculiar use of the expression notification.object?.title, because notification.object is not, of itself, a UIViewController. It is an AnyObject.
Now, an AnyObject has no known properties, so it has no title and your expression, it would seem, should not even compile. But, by a special dispensation coming from certain oddities of Objective-C, you are in fact allowed to ask about an AnyObject's properties anyway. But when you do, the result is itself an Optional, because no such property might exist.
Thus, you are actually testing, not the value of a view controller's title property, but whether this unknown object has a title property in the first place; and if in fact it does have a title property at all, the value of that title property is double-wrapped inside that Optional.
To see this clearly, just test this (silly) code:
let n = NSNotification(name: "Howdy", object: "Hi")
let t = n.object?.title
Look at what type t is. It is not a String?; it is a String??. That's your double-wrapped Optional. This means that it would be an Optional-wrapping-a-String in case this object turns out to have a title property, but just in case, that value has itself been wrapped in an Optional.
Thus, your test doesn't do what you want it to do. To do what you want to do, just speak much more plainly and simply. You need to cast the object to a UIViewController first, and then examine its title. Like this:
func aViewControllerDidLoad(notification:NSNotification) {
if let vc = notification.object as? UIViewController {
if vc.title != nil {
// ...
}
}
}
I am trying to send a double value from a UIView (which is loaded from a XIB) to a ViewController using a delegate
Here is my protocol, it is just sending a double to the main ViewController on a button click.
protocol HoursWorkedDelegate{
func sendHoursWorked(hoursWorked: Double);
}
class HoursWorkedView: UIView{
var delegate: HoursWorkedDelegate?;
#IBAction func calculateHoursWorked(sender: AnyObject){
// Do some calculations for the hoursWorked value
// Give value
delegate!.sendHoursWorked(hoursWorked);
}
}
// This class now wants that Double value
class ViewController: UIViewController, HoursWorkedDelegate{
// Conform to protocol
func sendHoursWorked(hoursWorked: Double){
// Lets say we just want to assign this value to a textField
hoursWorkedTextField.text = NSString(format: "%.4f", hoursWorked);
}
}
The error message I get is Thread 1: EXC_BAD_INSTRUCTION(code = EXC_I386_INVOP, subcode=0x0)
Any help would be much appreciated, Thank You!
As a start, change the exclamation point in this snippet to a question mark:
delegate!.sendHoursWorked(hoursWorked);
This is what's likely causing the crash, as you are force-unwrapping the optional delegate property. A question mark means we'll only call sendHoursWorked() on the delegate if the delegate exists.
That fix will now probably mean that your program is no longer crashing, but you still don't get the desired results, because sendHoursWorked() is never called. We have to tell our HoursWorkedView object who is delegating it.
Somewhere in your code, you might have something like this:
let hoursWorkedView = HoursWorkedView()
self.view.addSubview(hoursWorkedView)
It's right here where we should be setting the delegate:
let hoursWorkedView = HoursWorkedView()
hoursWorkedView.delegate = self
self.view.addSubview(hoursWorkedView)
Though if it's me, I probably add a constructor to HoursWorkedView that accepts the delegate property:
init(delegate: HoursWorkedDelegate) {
super.init()
self.delegate = delegate
}
And now we can just do this:
let hoursWorkedView = HoursWorkedView(delegate: self)
self.view.addSubview(hoursWorkedView)
I think you're getting your view and your viewcontroller mixed up: a ViewController controls things; a view just displays them. The viewController tells the view what to display.
So, you want to connect your button to the viewController -- not the view. And you don't need a custom view class or a delegate.
Set it up like this:
create a textField and a button
create an outlet for the textField
put calculateHoursWorked directly in your viewController
create an action to connect the button to calculateHoursWorked
in calculateHoursWorked, set self.textField.text to the result of the calculation (where "textField" is whatever you named your outlet)
You wouldn't use a delegate in this context because the viewController knows everything the view does. The delegate pattern is for cases where one object has no visibility into another.
EDIT:
That being said, the bug here is that the delegate isn't actually being set anywhere.
Swift Optionals (the ! and ?) help prevent cases like this. If you explicitly unwrap an optional using !, you have to make sure it's always defined. In this case, since delegate is defined as optional (?) you have to check it:
#IBAction func calculateHoursWorked(sender: AnyObject){
// Do some calculations for the hoursWorked value
// Give value
if let currentDelegate = self.delegate {
currentDelegate.sendHoursWorked(hoursWorked)
}
}