Kotlin: Iterate through a JSONArray
AndroidJsonKotlinAndroid Problem Overview
I'm writing an Android app using Kotlin and Realm. I have a JSONArray, and I want to iterate through the JSONObjects in this array in order to load them in a Realm database class:
Realm class:
import io.realm.RealmObject
import io.realm.annotations.PrimaryKey
import io.realm.annotations.Required
open class Person(
@PrimaryKey open var id: Long = 0,
@Required
open var name: String = ""
) : RealmObject() {
}
The JSONArray:
{
"persons":[
{
"id":0,
"name":"Biatrix"
},
{
"id":1,
"name":"Bill"
},
{
"id":2,
"name":"Oren"
},
{
"id":3,
"name":"Budd"
}
]
}
I've tried iterating like the following:
for (item : JSONObject in persons) {
}
... but I get a for-loop range must have an iterator() method
error.
Android Solutions
Solution 1 - Android
Unfortunately, JsonArray
does not expose an iterator. So you will have to iterate through it using an index range:
for (i in 0 until persons.length()) {
val item = persons.getJSONObject(i)
// Your code here
}
Solution 2 - Android
Even if some class doesn't expose an iterator
method, you can still iterate it with for
statement by providing an extension function iterator
:
operator fun JSONArray.iterator(): Iterator<JSONObject>
= (0 until length()).asSequence().map { get(it) as JSONObject }.iterator()
Now when you use JSONArray
in for
statement this extension is invoked to get an iterator. It creates a range of indices and maps each index to an item corresponding to this index.
I suppose the cast to JSONObject
is required as the array can contain not only objects but also primitives and other arrays. And the asSequence
call is here to execute map
operation in a lazy way.
Generic way (assuming all array entries are of same type)
@Suppress("UNCHECKED_CAST")
operator fun <T> JSONArray.iterator(): Iterator<T>
= (0 until length()).asSequence().map { get(it) as T }.iterator()
Solution 3 - Android
How about
(0..(jsonArray.length()-1)).forEach { i ->
var item = jsonArray.getJSONObject(i)
}
?
Solution 4 - Android
for (i in 0 until jsonArray.length()){
//do your stuff
}
Solution 5 - Android
shortest way is:
(0 until persons.length()).forEach {
val item = persons.getJSONObject(it)
Basically from a range taking from zero to the jsonarray lenght ,it takes one number at time and use it as a index to retrieve the current object