Kotlin Property Delegate for Fragment view lifecycle binding

ViewLifecycleBinding.kt

fun <T> Fragment.viewLifecycle(bindUntilEvent: Lifecycle.Event = Lifecycle.Event.ON_DESTROY): ReadWriteProperty<Fragment, T> =
        object: ReadWriteProperty<Fragment, T>, LifecycleObserver {

            // A backing property to hold our value
            private var binding: T? = null

            private var viewLifecycleOwner: LifecycleOwner? = null

            init {
                // Observe the View Lifecycle of the Fragment
                this@viewLifecycle
                    .viewLifecycleOwnerLiveData
                    .observe(this@viewLifecycle, Observer { newLifecycleOwner ->
                        viewLifecycleOwner
                            ?.lifecycle
                            ?.removeObserver(this)

                        viewLifecycleOwner = newLifecycleOwner.also {
                            it.lifecycle.addObserver(this)
                        }
                })
            }

            @OnLifecycleEvent(Lifecycle.Event.ON_ANY)
            fun onDestroy(event: Lifecycle.Event) {
                if (event == bindUntilEvent) {
                    // Clear out backing property just before onDestroyView
                    binding = null
                }
            }

            override fun getValue(
                thisRef: Fragment,
                property: KProperty<*>
            ): T {
                // Return the backing property if it's set
                return this.binding!!
            }
            override fun setValue(
                thisRef: Fragment,
                property: KProperty<*>,
                value: T
            ) {
                // Set the backing property
                this.binding = value
            }
        }
    }

    override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
        this.property = value
    }
}

Any overwritten methods in the LifecycleObserver shouldn't have any arguments in it. Just adjust the onDestroy to the following and remove the default value (bindUntilEvent) in the method definition like this:

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() {
        binding = null
    }

Fyi, in the lifecycle docs there are comments on not using the lifecycle annotations

If you use Java 7 Language, Lifecycle events are observed using annotations. Once Java 8 Language becomes mainstream on Android, annotations will be deprecated, so between DefaultLifecycleObserver and annotations, you must always prefer DefaultLifecycleObserver.

https://developer.android.com/reference/kotlin/androidx/lifecycle/Lifecycle#init

This can easily be rewritten to use DefaultLifecycleObserver instead though.

It seems there is an error in this part:

 override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
        this.property = value
    }

i've removed it in my sample app and it works.

In case anyone's interested, I refactored it to use DefaultLifecycleObserver https://gist.github.com/frel/5f3f928c27f4106ffd420a3d99c8037c

Apologies, I know this is incorrect and I've been meaning to update the blog post + gist. This is where I've settled - slightly more refined and reusable: https://gist.github.com/jamiesanson/478997780eb6ca93361df311058dc5c2