Chapter 15: Challenge 2 - Persisting the filter between app launches

📚 Official Books Combine: Asynchronous Programming with Swift
1

Persisting doesn’t work because didSet in Settings.keyworks is never called. Does anyone has an idea what goes wrong?

2

Apparently the line self.settings.keywords.append(new) in SettingsView is not triggering the didSet in the keywords property inside Settings model

3

Thanks miibpa,

do you think it’s a Swift bug?

taufi

4

Yep It seem to be a bug in Swift 5.2 :frowning:

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5

Read on ‘stackoverflow’ that structs like ‘FilterKeywords’ aren’t KVO compatible. The value has to be a subclass of NSObject using @objc dynamic properties. So adding a value in the array won’t trigger ‘willSet/didSet’

My solution was to use a temporary array instead and replace the whole array in the ‘AddKeywordView’ closure which triggered the ‘didSet’ method as expected.

//Reassign array to trigger ‘didSet’
let saveKeywords = self.settings.keywords + [new]
self.settings.keywords = saveKeywords

Another possible way is to use the underlying ‘wrappedValue’ of the binding property, maybe a hack…

self.$settings.keywords.wrappedValue = new

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6

@afrank Thank you for sharing your solution - much appreciated!