Combine .assign not working as intended?

Question

I'm trying to test out using combine with the UIScreen notifications, but the way I'm using .assign doesn't seem to working.

First, I defined a variable that stores whether a secondary display is available or not. I also added a debug print using didSet so I could check to see if the value was being changed.

class SceneDelegate: UIResponder, UIWindowSceneDelegate {    
    var secondaryDisplayAvailable = false {
        didSet {
            print("◆◆◆ secondaryDisplayAvailable did change to: \(secondaryDisplayAvailable)")
        }
    }

The following code compiles, but the value in secondaryDisplayAvailable does not get updated.

let _ = NotificationCenter.default.publisher(for: UIScreen.didConnectNotification)
    .map( {_ in return true} )
    .assign(to: \SceneDelegate.secondaryDisplayAvailable, on: self)

Assuming that my keypath is correct, when an additional screen is connected the value in secondaryDisplayAvailable should be updated.

If I change the code to update the variable using a keypath in .sink the value will get updated.

let _ = NotificationCenter.default.publisher(for: UIScreen.didConnectNotification)
     .map( {_ in return true} )
     .sink { (available) in
         self[keyPath: \.secondaryDisplayAvailable] = available
     }

Am I missing something about .assign or is this a bug?

iOS

1.5k

Posted by

sammyjojo

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Answer 1

Try adding receive(on:):

let _ = NotificationCenter.default.publisher(for: UIScreen.didConnectNotification) 
    .map( {_ in return true} ) 
    .receive(on: RunLoop.main)
    .assign(to: \SceneDelegate.secondaryDisplayAvailable, on: self)

It worked for me

Posted by

mikro098

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Combine .assign not working as intended?

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