How to get generic parameter class in Kotlin

Question

Firebase\'s snapshot.getValue() expects to be called as follows:

snapshot?.getValue(Person::class.java)

However I would like t

Answer 1

1. Using class comparison. See https://stackoverflow.com/a/61756761/2914140.

    inline fun  SharedPreferences.getData(key: String, defValue: Any? = null): T? =
        when (T::class) {
            Integer::class -> {
                val value = getInt(key, (defValue as? Int) ?: 0) as T
                if (value == 0) defValue as? T else value
            }
            Long::class -> {
                val value = getLong(key, (defValue as? Long) ?: 0L) as T
                if (value == 0) defValue as? T else value
            }
            Boolean::class -> {
                val value = getBoolean(key, (defValue as? Boolean) ?: false) as T
                if (value == false) defValue as? T else value
            }
            String::class -> getString(key, defValue as? String) as T?
            else -> throw IllegalStateException("Unsupported type")
        }
   

2. Using isAssignableFrom. See https://dev.to/cjbrooks12/kotlin-reified-generics-explained-3mie.

    inline fun  SharedPreferences.getData(key: String): T? {
        val cls = T::class.java
        return if (cls.isAssignableFrom(Integer::class.java)) {
            getInt(key, 0) as T
        } else if (cls.isAssignableFrom(Long::class.java)) {
            getLong(key, 0) as T
        } else {
            throw IllegalStateException("Unsupported type")
        }
    }
   

For Double in SharedPreferences see https://stackoverflow.com/a/45412036/2914140.

Use:

val s: String? = preferences.getData("key", "")
val i = preferences.getData("key")