Kotlin自动生成getter和setter,但我从未引用它们?同时,什么是Kotlin中编写自定义getter/setter的正确方式?当我说myObj.myVar = 99
时,我感觉像是直接访问myObj
的公共字段myVar
?这里实际上发生了什么?
Kotlin自动生成getter和setter,但我从未引用它们?同时,什么是Kotlin中编写自定义getter/setter的正确方式?当我说myObj.myVar = 99
时,我感觉像是直接访问myObj
的公共字段myVar
?这里实际上发生了什么?
这个问题已经在几个地方得到了解答,但我想为那些从Java / C# / C / C ++转换到Kotlin,并且有与我相同的疑问的人分享一个具体的例子:
我很难理解在Kotlin中getter和setter如何工作,特别是因为它们从未被显式调用(就像在Java中一样)。因此,我感到不舒服,因为看起来我们只是直接引用vars / vals作为字段。所以我进行了一项小实验,以证明这不是事实,并且实际上是在访问变量/值时在Kotlin中调用了隐式(自动生成的)或显式getter / setter。区别在于,您不需要显式请求默认的getter / setter。
来自文档 - 声明属性的完整语法如下:
var <propertyName>: <PropertyType> [= <property_initializer>]
[<getter>]
[<setter>]
我的例子是
class modifiersEg {
/** this will not compile unless:
* - we assign a default here
* - init it in the (or all, if multiple) constructor
* - insert the lateinit keyword */
var someNum: Int?
var someStr0: String = "hello"
var someStr1: String = "hello"
get() = field // field is actually this.someStr1, and 'this' is your class/obj instance
set(value) { field = value }
// kotlin actually creates the same setters and getters for someStr0
// as we explicitly created for someStr1
var someStr2: String? = "inital val"
set(value) { field = "ignore you" }
var someStr3: String = "inital val"
get() = "you'll never know what this var actually contains"
init {
someNum = 0
println(someStr2) // should print "inital val"
someStr2 = "blah blah blah"
println(someStr2) // should print "ignore you"
println(someStr3) // should print "you'll never know what this var actually contains"
}
我希望这能帮助其他一些人更好地理解。
以下是一些自定义 getter 和 setter 的实际应用示例。您可以在此处查看更多。
// Custom getter example
val friendlyDescription get(): String {
val isNeighborhood = district != null
var description = if (isNeighborhood) "Neighborhood" else "City"
description += " in"
if (isNeighborhood) {
description += " $city,"
}
province?.let {
if (it.isNotEmpty()) {
description += " $it,"
}
}
description += " $country"
return description
}
print(myLocation.friendlyDescription) // "Neighborhood in Denver, Colorado, United States"
// Custom setter example
enum class SearchResultType {
HISTORY, SAVED, BASIC
}
private lateinit var resultTypeString: String
var resultType: SearchResultType
get() {
return enumValueOf(resultTypeString)
}
set(value) {
resultTypeString = value.toString()
}
result.resultType = SearchResultType.HISTORY
print(result.resultTypeString) // "HISTORY"