Use the block based KVO API in AsyncOperation

[buggmagnet]

This change is 

[linear]

IOS-258 Fix swiftlint warning block_based_kvo

[pronebird]

It looks like observation API does not maintain a strong reference to target anymore. Try this in playground:

class MyOperation: Operation {
    private var observer: NSKeyValueObservation?

    override init() {
        super.init()

        observer = observe(\.isReady, changeHandler: { op, _ in
            print(op)
        })
    }

    deinit {
        print("deinit!")
    }
}

var op: MyOperation? = MyOperation()

op = nil

print("done")

[pronebird]

Any particular reason why that has to be marked dynamic?

[buggmagnet]

Reviewable status: 0 of 1 files reviewed, 2 unresolved discussions (waiting on @pronebird)

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ios/Operations/AsyncOperation.swift line 120 at r1 (raw file):

Previously, pronebird (Andrej Mihajlov) wrote…

Any particular reason why that has to be marked dynamic?

It's to force dynamic dispatching via the ObjC runtime which is required for KVO to work
Technically it has to be marked both @objc and dynamic but we inherit from NSObject so all our properties are already inherently @objc

This article shows an example on how to do it

---

ios/Operations/AsyncOperation.swift line 249 at r1 (raw file):

Previously, pronebird (Andrej Mihajlov) wrote…

It looks like observation API does not maintain a strong reference to target anymore. Try this in playground:

class MyOperation: Operation {
    private var observer: NSKeyValueObservation?

    override init() {
        super.init()

        observer = observe(\.isReady, changeHandler: { op, _ in
            print(op)
        })
    }

    deinit {
        print("deinit!")
    }
}

var op: MyOperation? = MyOperation()

op = nil

print("done")

I was under that impression too, but I used Instruments to make sure we were not leaking memory, and without that it would leak memory for each operation created.

You can run the check yourself if you want, remove the operation.isReadyObserver = nil line and run under instruments to see the result.

[pronebird]

Reviewed 1 of 1 files at r1, 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved