kotlin: when的用法

一，代码：

fun whenExample() {
    //例1，普通用法
    val number = 3
    when (number) {
        1 -> println("One")
        2 -> println("Two")
        3 -> println("Three")
        else -> println("Unknown")
    }
    //匹配多个条件
    val day = "Saturday"
    when (day) {
        "Saturday", "Sunday" -> println("Weekend")
        else -> println("Weekday")
    }
    //范围检查
    val score = 85
    when (score) {
        in 90..100 -> println("Excellent")
        in 75..89 -> println("Good")
        in 60..74 -> println("Pass")
        else -> println("Fail")
    }
    //类型检查
    val obj: Any = "Hello Kotlin"
    when (obj) {
        is String -> println("It's a String")
        is Int -> println("It's an Integer")
        else -> println("Unknown type")
    }
    //不带参数的when
    val number2 = 15
    when {
        number2 % 3 == 0 && number2 % 5 == 0 -> println("FizzBuzz")
        number2 % 3 == 0 -> println("Fizz")
        number2 % 5 == 0 -> println("Buzz")
        else -> println(number2)
    }
    //作为表达式使用返回一个值
    val score2 = 78
    val result = when (score2) {
        in 90..100 -> "A"
        in 80..89 -> "B"
        in 70..79 -> "C"
        else -> "D"
    }
    println("Grade: $result")
}

调用:

        //处理按钮点击事件
        binding.button1.setOnClickListener {
            whenExample()
        }

 

二，运行结果: