如何在一个类函数中使用来自多个构造函数的变量?-科特林

Question

我正在用不同的构造函数创建一个简单的数据类。我想让一个函数对两种实例类型都可以访问，而不需要写两次。如何做到这一点？

例如：

class myClass private constructor() {
constructor(
weather: String, 
day: Int?
) : this() {
//I can put assignment here
}
constructor(
day: Int?
) : this() {
//and here, but can this be done more efficiently?
}
val dayString: String = when(day) { //kotlin doesn't recognize 'day' variable here outside of constructors...
0 -> "Sunday"
1 -> "Monday"
2 -> "Tuesday"
3 -> "Wednesday"
4 -> "Thursday"
5 -> "Friday"
6 -> "Saturday"
else -> "Not a valid day of the week!"
}
}

Answer 1

所以当前day: Int?只是一个构造函数参数，而不是实例属性。您应该在主构造函数中将其声明为val day: Int?，以便dayString工作。当然，这只适用于主要(主(构造函数，您的类将如下所示：

class myClass private constructor(val day: Int?) {
constructor(
weather: String,
day: Int?
) : this(day) {
//I can put assignment here
}
val dayString: String = when(day) { //kotlin doesn't recognize 'day' variable here outside of constructors...
0 -> "Sunday"
1 -> "Monday"
2 -> "Tuesday"
3 -> "Wednesday"
4 -> "Thursday"
5 -> "Friday"
6 -> "Saturday"
else -> "Not a valid day of the week!"
}
}

如果你不喜欢这样：-为构造函数参数添加默认值，如val day: Int? = null-或添加要保存的互联网属性(如var _day: Int? = null(