delegates - Kotlin 委托(delegate)更有趣

Question

如果您知道 Google 的实验性 Android 架构组件，您可能知道 MutableLiveData .为了让它更有趣，我提供了:

class KotlinLiveData<T>(val default: T) {
    val data = MutableLiveData<T>()

    operator fun getValue(thisRef: Any?, property: KProperty<*>):T {
        return data.value ?: default
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value:T) {
        if (Looper.myLooper() == Looper.getMainLooper()) {
            data.value = value
        } else {
            data.postValue(value)
        }
    }
}

然后我可以:

var name : String by KotlinLiveData("not given")
name = "Chrzęszczybrzęczykiewicz"

但是，唉 - 这使得 data这是需要的，即注册 Observer无法访问:

name.data.observe(this, nameObserver) // won't work :(

知道我是否能以某种方式得到它？

Answer 1

感谢热键的解决方案，这里有一些更好的代码:

class KotlinLiveData<T>(val default: T, val liveData : MutableLiveData<T>? = null) {
    val data = liveData ?: MutableLiveData<T>()

    operator fun getValue(thisRef: Any?, property: KProperty<*>):T {
        return data.value ?: default
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value:T) {
        if (Looper.myLooper() == Looper.getMainLooper()) {
            data.value = value
        } else {
            data.postValue(value)
        }
    }
}

inline fun <reified R> KMutableProperty0<*>.getLiveData(): MutableLiveData<R> {
    isAccessible = true
    return (getDelegate() as KotlinLiveData<R>).data
}

inline fun <reified R> KMutableProperty0<*>.observe(owner: LifecycleOwner, obs : Observer<R>) {
    isAccessible = true
    (getDelegate() as KotlinLiveData<R>).data.observe(owner,obs)
}

现在我能:
someViewModel::name.observe(myActivity, Observer<String>{...})
和
someViewModel.name = "Kowalski, Leon"
按预期工作

此类允许使用 LiveData 和 Android 数据绑定(bind)开箱即用。