4.0 数据类

我们使用的是不可修改的对象，当我们需要修改这个对象状态，我们可以拷贝一个对象只修改需要修改的属性

        val f1 = Forecast(Date(), 27.5f, "Shiny day")
        val f2 = f1.copy(temperature = 30f)

映射对象的每一个属性到一个变量中，这个过程就是多声明，例如：

val f1 = Forecast(Date(), 27.5f, "Shiny day")
val (date, temperature, details) = f1
这个多声明编译之后就是这样的：
val date = f1.component1()
val temperature = f1.component2()
val details = f1.component3()

接下来，我们来获取天气数据，组成一个列表
先来获取数据，有数据，就需要数据类来承载数据，定义数据类：

data class Temperature(val day: Float, val min: Float, val max: Float, val night: Float, val eve: Float, val morn: Float)
data class ForecastResult(val city: City, val list: List)
data class Forecast(val dt: Long, val temp: Temperature, val pressure: Float, val humidity: Int, val weather: List, val speed: Float, val deg: Int, val clouds: Int, val rain: Float)
data class Coordinates(val lon: Float, val lat: Float)
data class City(val id: Long, val name: String, val coord: Coordinates, val country: String, val population: Int)
data class Weather(val id: Long, val main: String, val description: String, val icon: String)

然后获取json数据，转换json到数据类

    public class ForecastRequest(val zipCode: String) {
        //companion object中可以一些静态的属性、常量或者函数，这个对象被这个类所有对象共享
        companion object {
            private val APP_ID = "15646a06818f61f7b8d7823ca833e1ce"
            private val URL = "http://api.openweathermap.org/data/2.5/" + "forecast/daily?mode=json&units=metric&cnt=7"
            private val COMPLETE_URL = "$URL&APPID=$APP_ID&q="
        }
        fun execute(): ForecastResult {
            val forecastJsonStr = URL(COMPLETE_URL + zipCode).readText()
            return Gson().fromJson(forecastJsonStr, ForecastResult::class.java)
        }
    }

在类中记得导入import java.net.URL，然后gradle中引入anko

在这里，我们需要转换一下数据

//如果有两个相同名字的类，可以给起个别名
import com.kavenka.testkotlin.domain.Forecast as ModelForecast

public class ForecastDataMapper {
    fun convertFromDataModel(forecast: ForecastResult): ForecastList {
        return ForecastList(forecast.city.name, forecast.city.country, convertForecastListToDomain(forecast.list))
    }

    private fun convertForecastListToDomain(list: List): List {
        //list.map可以循环这个集合并且返回一个转换后的新的list
        return list.map { convertForecastItemToDomain(it) }
    }

    private fun convertForecastItemToDomain(forecast: Forecast): ModelForecast {
        return ModelForecast(convertDate(forecast.dt), forecast.weather[0].description, forecast.temp.max.toInt(), forecast.temp.min.toInt())
    }

    private fun convertDate(date: Long): String {
        val df = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.getDefault())
        return df.format(date * 1000)
    }
}

创建一个执行任务的接口类，在创建一个实现这个接口的请求数据类：

public interface Command {
    fun execute(): T
}

class RequestForecastCommand(val zipCode: String) : Command {
    override fun execute(): ForecastList {
        val forecastRequest = ForecastRequest(zipCode)
        return ForecastDataMapper().convertFromDataModel(
                forecastRequest.execute())
    }
}

上面的步骤其实就是1.定义数据类，2.包装数据类，3.定义请求数据接口，4.获取数据转化为数据实体类

最后，将数据和recycleView绑定

class ForecastListAdapter(val weekForecast: ForecastList) : RecyclerView.Adapter() {
    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"
        }
    }
    override fun getItemCount(): Int = weekForecast.dailyForecast.size
    class ViewHolder(val textView: TextView) : RecyclerView.ViewHolder(textView)
}

使用anko获取数据，后续将重点学习介绍一下anko
        doAsync() {
            val result = RequestForecastCommand("94043").execute()
            uiThread {
                forecastList.adapter = ForecastListAdapter(result)
            }
        }

最后的运行效果：

png1.png