Kotlin技巧與自定義語法糖

Kotlin技巧與自定義語法糖

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kotlin,ktx,anko

kotlin官方中文站：http://www.kotlincn.net/docs/reference/basic-syntax.html
ktx google官網：https://developer.android.google.cn/kotlin/ktx
anko github地址：https://github.com/Kotlin/anko

kotlin數組使用

不用使用String[]; 需要使用arrayOf()

//1.數組和集合定義
val names = arrayOf<String>("2", "3")
val ages = listOf<Int>(1, 2, 3)
//訪問
names[0]
ages[0]
//MutableList()和List

使用if,when表達式簡化代碼

//2.使用if,when表達式返回值
val invalid = isInvalid(2)
val age = getAge("x")
private fun isInvalid(num: Int): Boolean =
        if (num > 3) {
            true
        } else if (num > 2) {
            false
        } else {
            false
        }
private fun getAge(name: String): Int {
    return when (name) {
        "xx" -> 3
        else -> 10
    }
}

減少重載方法，使用參數默認值

//3.使用函數默認參數
createUser("xx", 3)
createUser("qq")
private fun createUser(name: String, age: Int = 18) {
}

steam式操作

//4.steam流式操作
ages.filter { it > 3 }.map { (it * 3).toString() }.forEach { print(it) }

kotlin內部類與嵌套類

//5.內部類和嵌套類
MainInterface().fetchContext().takeIf { it == this }
MainEntity().fetchContext().takeIf { it == null }
//inner內部類，持有外部實例，可以調用外部方法
inner class MainInterface {
    fun fetchContext(): Context {
        return this@MainActivity
    }
}
//嵌套類，只是寫在一個文件裏面，和另寫一個文件沒區別
class MainEntity {
    fun fetchContext(): Context? {
        //報錯，找不到MainActivity實例
          return this@MainActivity
        return null
    }
}

foreach break

//6.foreach
ages.forEach {
    if (it > 3) {
        for (name in names) {
            if (name == "xx") {
                continue
            }
            break
        }
    }
}

高階函數與lambda

//7.高階函數與lambda
AlertDialog.Builder(this)
        .setTitle("提示")
        .setMessage("有新版本升級@")
        .setCancelable(true)
        .setPositiveButton("確定") { dialog, _ ->
            //跳轉頁面
            dialog.dismiss()
        }
        .create()
        .show()
val alertDialog = showDialog {
    setTitle("提示")
    setMessage("")
    setCancelable(true)
    setPositiveButton("確定") { dialog, _ ->
        //跳轉頁面
        dialog.dismiss()
    }
}
val alertDialog1 = showDialog1 {
    it.setTitle("提示")
    it.setMessage("")
    it.setCancelable(true)
    it.setPositiveButton("確定") { dialog, _ ->
        //跳轉頁面
        dialog.dismiss()
    }
}

private fun showDialog(block: AlertDialog.Builder.() -> Unit): AlertDialog {
    val builder = AlertDialog.Builder(this)
    block.invoke(builder)
    val alertDialog = builder.create()
    alertDialog.show()
    return alertDialog
}
private fun showDialog1(block: (AlertDialog.Builder) -> Unit): AlertDialog {
    val builder = AlertDialog.Builder(this)
    block.invoke(builder)
    val alertDialog = builder.create()
    alertDialog.show()
    return alertDialog
}

handler.post()和handler.post{}區別

實戰1

//8.實戰1：創建jsonObject封裝
val jsonObject = JSONObject()
jsonObject.put("key1", "value1")
jsonObject.put("key2", "value2")
createJson(
        "key1" to "value1",
        "key2" to 1001,
        "key2" to createJson(
                "inner1" to ""
        )
)
private fun <V> createJson(vararg pairs: Pair<String, V>): JSONObject =
        JSONObject().apply {
            for ((key, value) in pairs) {
                put(key, value)
            }
        }

實戰2

//8.實戰2：Notification封裝
val builder = NotificationCompat.Builder(this, "")
        .setSmallIcon(R.mipmap.ic_launcher)
        .setContentTitle("通知")
        .setContentText("有新版本更新！")
        .setPriority(NotificationCompat.PRIORITY_DEFAULT)
NotificationManagerCompat.from(this).notify(1,builder.build())

自定義View時構造函數問題

class ChapterListView @JvmOverloads constructor(
    val mContext: Context, attrs: AttributeSet? = null
) : LinearLayout(mContext, attrs) {}

Kotlin 重載個方法,還有兩幅面孔，省代碼的同時也帶來一個深坑 | Kotlin 原理

kotlin小技巧

1. 函數內部定義函數,縮小方法作用域
2. AbDialog 類似高階函數 lambda