【kotlin】Kotlin笔记18-高阶函数的应用

Love The Way You Lie 2022-11-18 02:24 186阅读 0赞

### Kotlin笔记18-高阶函数的应用 ###

**11.1 高阶函数的应用**

*  **简化SharedPreferences**

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th align="left">向SharePreferences存储数据的过程</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td align="left">调用其edit()方法获取SharedPreferences.Editor对象</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td align="left">向SharePreferences.Editor对象中添加数据</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td align="left">调用apply()方法将添加的数据提交,完成数据存储操作</td> 
  </tr> 
 </tbody> 
</table>

`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:`

1.  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")
    }

1.  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**

<table> 
 <thead> 
  <tr> 
   <th>名称</th> 
   <th>作用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>ContentValues</td> 
   <td>结合SQLiteDataBase的API存储和修改数据库中的数据</td> 
  </tr> 
 </tbody> 
</table>

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**

1.  在kotlin中使用"Apple" to 1这样的语法结构快速创建一个键值对,会创建一个Pair对象