Kotlin Recursive Extension Function To Walk Android View Hierarchy

I am attempting to create a generic extension function that can walk an Android view hierarchy and return the first occurence of a view of a specific type. The idea would be to in

Solution 1:

I'm gonna add a little bit to Victor Rendina's answer.

You can have two functions: one with the clazz: Class<T> parameter and the other one inline with reified generic:

inlinefun<reified T : View> View.findFirstChildRecursive(): T? {
    return findFirstChildRecursive(T::class.java)
}

fun<T: View> View.findFirstChildRecursive(clazz: Class<T>): T? {
    if (this::class.java == clazz) {
        @Suppress("UNCHECKED_CAST")returnthisas T
    } elseif (thisis ViewGroup) {
        for (i in0 until childCount) {
            getChildAt(i).findFirstChildRecursive(clazz)?.let { return it }
        }
    }
    returnnull
}

Solution 2:

Basically the bottom line is Kotlin doesn't allow you to inline recursive functions because it could potentially have to inline an infinite number of calls.

See this related post:Can a recursive function be inline?

The method above also can not be a tailrec function because calling itself is not the last operation in the function.

See the Kotlin function docs here:https://kotlinlang.org/docs/reference/functions.html

If you still want to achieve something similar, you can pass the class into the function.

val someView = parentView.findFirstChildRecursive(Toolbar::class.java)

fun<T: View> View.findFirstChildRecursive(clazz: Class<T>): T? {
    if (this::class.java == clazz) {
        @Suppress("UNCHECKED_CAST")returnthisas T
    } elseif (thisis ViewGroup) {
        for (i in0 until childCount) {
            getChildAt(i).findFirstChildRecursive(clazz)?.let { return it }
        }
    }
    returnnull
}