Android kotlin应用

1 Anko 异步

async() {
Request(url).run()
uiThread { longToast("Request performed") }
}

2 单例

1--------------
class App : Application() {
companion object {
private var instance: Application? = null
fun instance() = instance!!
}
override fun onCreate() {
super.onCreate()
instance = this
}
}

2------------
class App : Application() {
companion object {
var instance: App by Delegates.notNull()
}
override fun onCreate() {
super.onCreate()
instance = this
}
}

3 lazy 数据库

class App : Application() {
val database: SQLiteOpenHelper by lazy {
MyDatabaseHelper(applicationContext)
}
override fun onCreate() {
super.onCreate()
val db = database.writableDatabase
}
}

4 ManagedSqliteOpenHelper

public fun  use(f: SQLiteDatabase.() -> T): T {
try {
return openDatabase().f()
} finally {
closeDatabase()
}
}

val result = forecastDbHelper.use {
val queriedObject = ...
queriedObject
}

use 接收一个 SQLiteDatabase 的扩展函数。这表示，我们可以使
用 this 在大括号中，并且处于 SQLiteDatabase 对象中。

定义表

object CityForecastTable {
val NAME = "CityForecast"
val ID = "_id"
val CITY = "city"
val COUNTRY = "country"
}

object DayForecastTable {
val NAME = "DayForecast"
val ID = "_id"
val DATE = "date"
val DESCRIPTION = "description"
val HIGH = "high"
val LOW = "low"
val ICON_URL = "iconUrl"
val CITY_ID = "cityId"
}


继承ManagedSQLiteOpenHelper
class ForecastDbHelper() : ManagedSQLiteOpenHelper(App.instance,
ForecastDbHelper.DB_NAME, null, ForecastDbHelper.DB_VERS
ION) {
...
}


companion object {
val DB_NAME = "forecast.db"
val DB_VERSION = 1
val instance: ForecastDbHelper by lazy { ForecastDbHelper()
}