Kotlin 如何通过反射判断该字段是否可以为空

发布于10月27日

I'm developing a code generator that takes the data from the classes during runtime. This generator is designed to work only with Kotlin. At the moment, I was faced with the problem, as I don't know how to check if the field is nullable.

So the main question is how to implement this check via reflection?

推荐答案

You can check nullability with isMarkedNullable. The following code:

class MyClass(val nullable: Long?, val notNullable: MyClass)
MyClass::class.declaredMemberProperties.forEach {
    println("Property $it isMarkedNullable=${it.returnType.isMarkedNullable}")
}

将打印:

Property val MyClass.notNullable: stack.MyClass isMarkedNullable=false
Property val MyClass.nullable: kotlin.Long? isMarkedNullable=true

摘自documentation(我的重点):

对于Kotlin类型，这意味着允许使用null值

Note that even if isMarkedNullable is false, values of the type can still be null. This may happen if it is a type of the type parameter with a nullable upper bound:
fun <T> foo(t: T) {
    // isMarkedNullable == false for t's type, but t can be null here 
}