简化前面的的天气列表的例子，在ForecastList.kt这个类中，实现一个get方法，还有一个size方法：
data class ForecastList(val city: String, val country: String, val dailyForecast: List<com.kavenka.testkotlin.domain.Forecast>) {
operator fun get(position: Int): Forecast = dailyForecast[position]
fun size(): Int = dailyForecast.size
}
然后在我们的adapter类中，我们可以写得更简单一点
class ForecastListAdapter(val weekForecast: ForecastList) : RecyclerView.Adapter<ForecastListAdapter.ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(TextView(parent.getContext()))
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
// with(weekForecast.dailyForecast[position]) {
// holder.textView.text = "$date - $description - $high/$low"
// }
with(weekForecast[position]) {
holder.textView.text = "$date - $description - $high/$low"
}
}
// override fun getItemCount(): Int = weekForecast.dailyForecast.size
override fun getItemCount(): Int = weekForecast.size()
class ViewHolder(val textView: TextView) : RecyclerView.ViewHolder(textView)
}
将dailyForecast的每一项对应的赋值给ForecastList，在外部访问ForecastList的item时，实际获取的是dailyForecast的item。size方法也是一样。
扩展函数的操作符
定义ViewGroup的扩展函数get，使其可以直接访问ViewGroup中的子view
operator fun ViewGroup.get(position: Int): View = getChildAt(position)
现在真的可以非常简单地从一个 ViewGroup 中通过position得到一个view
val container: ViewGroup = find(R.id.container)
val view = container[2]
