kotlin流程控制

if表达式可实现赋值操作：

val z = if (condition) x else y

when表达式代替switch/case

when (x){
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> {
        print("I'm a block")
        print("x is neither 1 nor 2")
    }
}

val result = when (x) {
    0, 1 -> "binary"
    else -> "error"
}

when(view) {
    is TextView -> view.setText("I'm a TextView")
    is EditText -> toast("EditText value: ${view.getText()}")
    is ViewGroup -> toast("Number of children: ${view.getChildCount()} ")
    else -> view.visibility = View.GONE
}

val cost = when(x) {
    in 1..10 -> "cheap"
    in 10..100 -> "regular"
    in 100..1000 -> "expensive"
    in specialValues -> "special value!"
    else -> "not rated"
}

val res = when{
    x in 1..10 -> "cheap"
    s.contains("hello") -> "it's a welcome!"
    v is ViewGroup -> "child count: ${v.getChildCount()}"
    else -> ""
}

Range 表达式使用一个 .. 操作符，它是被定义实现了一个 RangTo 方法。Ranges 帮助我们使用很多富有创造性的方式去简化我们的代码。比如我们可以把它：

if(i >= 0 && i <= 10) println(i)

转化成：

if (i in 0..10) println(i)