Passing data from one view controller to the third directly - ios

Question

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.

Answer 1

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.

Answer 2

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.