Kotlin代表更有趣

你可以 access the delegate object 并获得 MutableLiveData<T> 从中:

inline fun <reified R> KProperty<*>.delegateAs<R>(): R? {
    isAccessible = true
    return getDelegate() as? R
}

::name.delegateAs<KotlinLiveData<String>>?.data?.observe(this, nameObserver)

^{要引用成员属性,请使用 this::name 或 someInstance::name .}

此解决方案需要您添加Kotlin反射API, kotlin-reflect ,作为项目的依赖项。此外,由于类型擦除 .delegateAs<KotlinLiveData<String>> 调用不是类型安全的:它只能检查委托是否是 KotlinLiveData<*> String .

多亏了hotkey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)
}

现在我可以:

someViewModel::name.observe(myActivity, Observer<String>{...})

具有

someViewModel.name = "Kowalski, Leon"

这个类支持使用LiveData和Android数据绑定。

您可以实现的最简单方法是将委托人设置为字段,例如:

@JvmField val dataOfName =  KotlinLiveData("not given")
var name : String by dataOfName

然后可以在类中使用实时数据,例如:

dataOfName.data.observe(this, nameObserver)
name = "Chrzęszczybrzęczykiewicz"

或

var name : String by live("not given").observe(this, nameObserver)

笔记 你可以 nameObserver

val observers by lazy{mutableListOf<Observer>()}
var name : String by live("not given").observe(this){data->
    observers.forEach{it.dataChanged(data)}
}

observers+= nameObserver;

name = "Chrzęszczybrzęczykiewicz"

observers-= nameObserver;