【kotlin】Kotlin笔记18-高阶函数的应用

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mozhimen 2022-06-23 18:34:38 ©著作权

文章标签 android kotlin 高阶函数数据键值对 文章分类 Java 编程语言

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【kotlin】Kotlin笔记18-高阶函数的应用
https://blog.51cto.com/mozhimen/5412515

Kotlin笔记18-高阶函数的应用

11.1 高阶函数的应用

简化SharedPreferences

序号	向SharePreferences存储数据的过程
1	调用其edit()方法获取SharedPreferences.Editor对象
2	向SharePreferences.Editor对象中添加数据
3	调用apply()方法将添加的数据提交,完成数据存储操作

描述转化成代码:

val edior=getSharedPreferences("data",Context.MODE_PRIVATE).edit()
editor.putString("name", "Tom")
editor.putInt("age", 28)
editor.putBoolean("married", false)
editor.apply()

使用高阶函数简化:

新建SharePreferences文件

fun SharePreferences.open(block: SharePreferences.Editor() -> Unit) {
  val editor = edit()
  editor.block()
  editor.apply()
}

用法:

getSharedPreferences("data", Context.MODE_PRIVATE).open {
  putString("name","Tom")
}

KTX扩展库已经包含这种简化用法,也可以使用

Example:

getSharedPreferences("data", Context.MODE_PRIVATE).edit{
  putString("name","Tom")
}

简化ContentValues

名称	作用
ContentValues	结合SQLiteDataBase的API存储和修改数据库中的数据

val values = ContentValues()
values.put("name", "Game of Thrones")
values.put("author","George Martin")
values.put("pages", 720)
values.put("price", 20.85)
db.insert("Book", null, values)

简化1:

fun cvOf(vararg pairs: Pair<String, Any?>): ContentValues {
    val cv = ContentValues()
    for (pair in pairs) {
        val key = pair.first
        when (val value = pair.second) {
            is Int -> cv.put(key, value)
            is Long -> cv.put(key, value)
            is Float -> cv.put(key, value)
            is Double -> cv.put(key, value)
            is Boolean -> cv.put(key, value)
            is String -> cv.put(key, value)
            is Byte -> cv.put(key, value)
            is ByteArray -> cv.put(key, value)
            null -> cv.putNull(key)
        }
    }
    return cv
}

用法:

val values= cvOf("name" to "Game of Thrones","author" to "George Martin","pages" to 720, "price" to 20.85)
db.insert("Book",null,values)

代码优化:

fun cvOf(vararg pairs: Pair<String, Any?>) = ContentValues().apply {
    for (pair in pairs) {
        val key = pair.first
        when (val value = pair.second) {
            is Int -> put(key, value)
            is Long -> put(key, value)
            is Float -> put(key, value)
            is Double -> put(key, value)
            is Boolean -> put(key, value)
            is String -> put(key, value)
            is Byte -> put(key, value)
            is ByteArray -> put(key, value)
            null -> putNull(key)
        }
    }
}

KTX库中也提供了同样的功能的contentValuesOf()方法,用法如下:

val  values = contentValuesOf("name" to "Game of Thrones","author" to "George Martin", "pages" to 720,"price" to 20.85)
db.insert("Book", null, values)

ヾ(≧▽≦!)o Kotlin新特性