Gson Utils by Kotlin

GsonUtils.kt

//convert gson String to Map<K, V>. Crash when invalid structure found
inline fun <reified K, reified V> String.toMapByGson(): Map<K, V> = if (isNotEmpty()) {
    Gson().fromJson<HashMap<K, V>>(this, TypeToken.getParameterized(HashMap::class.java, K::class.java, V::class.java).type)
} else {
    mapOf<K, V>()
}

//convert gson String to List<T>. Crash when invalid structure found
inline fun <reified T> String.toListByGson(): List<T> = if (isNotEmpty()) {
    Gson().fromJson<List<T>>(this, TypeToken.getParameterized(ArrayList::class.java, T::class.java).type)
} else {
    listOf<T>()
}


//convert gson String to T. Crash when invalid structure found
inline fun <reified T> String.toObjectByGson(): T = Gson().fromJson<T>(this, T::class.java)

//convert gson String to T. Crash when invalid structure found
fun <T> String.toObjectByGson(cls: Class<T>): T = Gson().instance.fromJson<T>(this, cls)

//convert T to String
fun Any.toStringByGson(): String = Gson().toJson(this)

/**
 * persistence property that is convertable to Gson String on Fragment.
 * The set value also write to Fragment.arguments, and always read from Fragment.arguments if need.
 */
class GsonableProperty<T : Any>(private val defaultValue: T? = null, private val cls: Class<T>) : kotlin.properties.ReadWriteProperty<Fragment, T> {

    var value: T? = null

    override operator fun getValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>): T {
        if (value == null) {
            val args = thisRef.arguments ?: throw IllegalStateException("Cannot read property ${property.name} if no arguments have been set")
            @Suppress("UNCHECKED_CAST")
            value = args.getString(property.name).toObjectByGson(cls)
        }
        return (value ?: defaultValue) ?: throw IllegalStateException("Property ${property.name} could not be read")
    }

    override operator fun setValue(thisRef: android.support.v4.app.Fragment, property: kotlin.reflect.KProperty<*>, value: T) {
        val args = thisRef.arguments?.let {
            it
        } ?: run {
            Bundle().also {
                thisRef.arguments = it
            }
        }

        val key = property.name

        this.value = value

        args.putString(key, value.toStringByGson())
    }
}