好久沒有更新啦，今天學習了一些kotlin的語法

class MainActivity : AppCompatActivity() {

    private val testArray: ArrayList<String> by lazy { ArrayList<String>() }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.i("hello", "let = " + testLet().toString())
        Log.i("hello", "apply = " + testApply().toString())
        Log.i("hello", "with = " + testWith())
        Log.i("hello", "run = " + testRun())

        testRun2()
        testAlso()
        testRepeat()

        Log.i("hello", "takeIf = " + testTakeIf())
        Log.i("hello", "takeUnless = " + testTakeUnless())

        6.takeIf { it < 7 }?.let {
            compareValues(1, 2)
            Log.i("hello", "2 method = $it")
        }
    }

    private fun testLet(): ArrayList<String> {
        //T.let 將T作為it，let的返回值為函式體內最後一條語句的返回值
        testArray.let {
            it.add("let1")
            it.add("let2")
            Log.i("hello", it.toString())
            return it
        }
    }

    private fun testApply(): ArrayList<String> {
        //T.apply T將函式體中的每一條語句按順序執行，返回T
        return testArray.apply {
            add("apply3")
            add("apply4")
            add("apply5")
            remove("let1")
            Log.i("hello", "apply this=" + this)
        }
    }

    private fun testWith(): Boolean {
        //with(T) 將函式體中的每一條語句按順序執行，返回值為函式體內最後一條語句的返回值
        return with(testArray) {
            add("with6")
            add("with7")
            remove("apply8")
        }
    }

    private fun testRun(): Int {
        //T.run T將函式體中的每一條語句按順序執行，返回最後一條語句的返回值
        return testArray.run {
            add("run9")
            add("run10")
            Log.i("hello", "run this=" + this)
            remove("let1")
            compareValues(3, 4)
        }
    }

    private fun testRun2() {
        //kotlin中的run函式，返回最後一句語句的返回
        var i = 1
        val date = kotlin.run {
            i++
            Date()
            //compareValues(2,3)
        }
        Log.i("hello", "run2 = $date")
    }

    private fun testAlso() {
        //T.also T作為it，返回T
        val also = Date().also {
            Log.i("hello", "also this = $it")
            testArray.add("also11")
        }
        Log.i("hello", "also = $also")
    }

    private fun testRepeat() {
        //其中it為次數，如此處i分別為 0，1，2 repeat 返回Unit
        repeat(3) {
            Log.i("hello", "repeat = $it")
        }
    }

    private fun testTakeIf(): Int? {
        //T.takeIf 當T滿足if條件時返回T，否則返回null
        return 6.takeIf {
            it < 5
        }
    }

    private fun testTakeUnless(): Int? {
        //T.takeIf 當T不滿足條件時返回T，滿足條件返回null
        return 6.takeUnless {
            it < 5
        }
    }
}
 

自己動手實現一下，感覺理解了一些，一起加油鴨～