Question

我正在尝试代理Observables和LiveData的调用（类似于Mediator模式），但我找不到类型安全的解决方案。这就是问题所在：

class Proxy {
    private val backupMap = HashMap<LiveData<Any>, Observer<Any>>()

     fun <T> add(liveData : LiveData<T>, observer : Observer<T>) {
         // !This is the issue LiveData<Any> is expected
         backupMap.put(liveData, observer)
     }

    fun attach() {
        backupMap.forEach { (key, value) ->
            key.observeForever(value)
        }
    }
}

fun addSome() {
    Proxy().apply {
        add(MutableLiveData<String>(), Observer {  })
    }
}

我可以将backupMap.put投放到backupMap.put(liveData as LiveData<Any>, observer as Observer<Any>)，但这会导致Unchecked Cast。

Answer 1

我发现的解决方案是使用中间对象来保存类型安全绑定：

private  val backupMap: MutableMap<LiveData<*>, Attacher<*>> 

private class Attacher<A>(private val lifeData: LiveData<A>, private val observer : Observer<A>) {
        fun attach() {
            lifeData.observeForever(observer)
        }

        fun detach() {
            lifeData.removeObserver(observer)
        }
    }

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