Kotlin中调用父类内部类（ImageSwitcher.LayoutParams）失效求助

Great question! This difference comes down to how Java and Kotlin handle inheritance of nested classes—here's a breakdown of the key rules:

• Java's implicit nested class access
  In Java, when a subclass (like ImageSwitcher) extends a parent class (like FrameLayout), non-private nested classes of the parent (such as FrameLayout.LayoutParams) are implicitly "inherited" in a syntactic sense. The compiler lets you reference the parent's nested class using the subclass's name as a shortcut—so ImageSwitcher.LayoutParams is just sugar that resolves to FrameLayout.LayoutParams under the hood. Java does this to make code feel more intuitive when working with subclass APIs.

• Kotlin's strict nested class resolution
  Kotlin takes a more explicit approach to nested class access. It does not automatically expose a parent's nested class as part of the subclass's namespace. Since ImageSwitcher doesn't define its own LayoutParams inner class, writing ImageSwitcher.LayoutParams throws a compilation error—Kotlin won't assume you're referring to the parent class's nested type. You have to explicitly use FrameLayout.LayoutParams to reference the correct class.

• Kotlin's design choice: avoiding ambiguity
  This strictness is intentional. If ImageSwitcher ever defined its own LayoutParams inner class later, ImageSwitcher.LayoutParams would clearly point to the subclass's version. Java's implicit behavior, by contrast, could lead to confusing or unexpected references if a subclass adds a nested class with the same name later. Kotlin eliminates that ambiguity by requiring explicit qualification.

In short: Java allows lenient, implicit access to a parent's nested classes via a subclass, while Kotlin enforces explicit, unambiguous references to avoid confusion.

内容的提问来源于stack exchange，提问作者humazed