Type inference failed, how to fix?

# android

[Alan Yin]

Type inference failed, how to fix?

[Alan Yin]

class LiveEvent<T> : MediatorLiveData<T>() {

    private val observers = ArraySet<ObserverWrapper<in T>>()

    @MainThread
    override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
        val wrapper = ObserverWrapper(observer)
        observers.add(wrapper)
        super.observe(owner, wrapper)
    }

    @MainThread
    override fun observeForever(observer: Observer<in T>) {
        val wrapper = ObserverWrapper(observer)
        observers.add(wrapper)
        super.observeForever(wrapper)
    }

    @MainThread
    override fun removeObserver(observer: Observer<in T>) {
        if (observers.remove(observer)) { // Here, type inference failed
            super.removeObserver(observer)
            return
        }
        val iterator = observers.iterator()
        while (iterator.hasNext()) {
            val wrapper = iterator.next()
            if (wrapper.observer == observer) {
                iterator.remove()
                super.removeObserver(wrapper)
                break
            }
        }
    }

    @MainThread
    override fun setValue(t: T?) {
        observers.forEach { it.newValue() }
        super.setValue(t)
    }

    private class ObserverWrapper<T>(val observer: Observer<T>) : Observer<T> {

        private var pending = false

        override fun onChanged(t: T?) {
            if (pending) {
                pending = false
                observer.onChanged(t)
            }
        }

        fun newValue() {
            pending = true
        }
    }
}

[Alan Yin]

Type inference failed. The value of the type parameter T should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.

[gildor]

Oh which line?

[Alan Yin]

@gildor removeObserver

[gildor]

It looks for me as an issue with generics unfortunately, remove extension has type out T and your element has in T. It looks like an issue of Kotlin, I would create an issue about it, because similar code works fine with java, also error message is not correct

[Sam]

Can you not just explicitly specify the type param?

[gildor]

no, there is no type param on this method, type param is from receiver