Swift: Cannot add element in Array from another object

Question

I am struggeling with swift syntax . I want to add objects to an array but I have syntax errors. The array is located in class Document, and the class that should add objects is in class Viewcontroller.

The array is of type Content:

public class Content: NSObject  {
    @objc var bankAccSender: String?
    @objc var bankAccReceiver: String?

Declaration snippest in Document:

class Document: NSDocument  {
    
    var content=[Content]()

    override init() {
        super.init()
        self.content = [Content]()
        
        // force one data record to insert into  content 
        content += [Content (… )]      // checked with debugger

The ViewController has assigned the represented Object

contentVC.representedObject = content

But adding data in ViewController gives a compiler error „Type of expression is ambiguous without more context“:

var posting = Content(…)
self.representedObject.append(posting)

Hope you can help..

Leo Dabus · Accepted Answer · 2020-10-23 19:30:44Z

2

You can't append an element to an object of type Any. What you need is to replace the existing value with a new collection:

representedObject = (representedObject as? [Content] ?? []) + CollectionOfOne(posting)

answered Oct 23, 2020 at 19:30

Leo Dabus

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1 Comment

Christian Krueger Over a year ago

Thanks Rob, it is really tricky. Unfortunately, both of your statements raises errors. Statement is : "Cannot use mutating member on immutable value of type [content]". I will see if Leo's answer helps.

Rob Napier · Accepted Answer · 2020-10-23 14:52:13Z

representedObject is of type Any?, which is a very difficult type to work with in Swift. Since you already have a content property, I would probably adjust that, and then re-assign it to representedObject.

You can also try this (untested), as long as you are certain that the type is always [Content]:

(self.representedObject as! [Content]).append(posting)

It's possible you'll need some more complex like this:

(self.representedObject as! [Content]?)!.append(posting)

As I said, Any? is an incredibly obnoxious type. You probably want to wrap this up into a function. Or I you can avoid using representedObject, then I would recommend that. In many cases you don't need it. It's often just a convenience (in ObjC; in Swift, it's very hard to use).

Thanks Rob, it is really tricky. Unfortunately, both of you statements raises errors.

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