How to iterate through SparseArray?

Question

Is there a way to iterate over Java SparseArray (for Android) ? I used sparsearray to easily get values by index. I could not find one.

Answer 1

If you use Kotlin, you can use extension functions as such, for example:

fun  LongSparseArray.valuesIterator(): Iterator {
    val nSize = this.size()
    return object : Iterator {
        var i = 0
        override fun hasNext(): Boolean = i < nSize
        override fun next(): T = valueAt(i++)
    }
}

fun  LongSparseArray.keysIterator(): Iterator {
    val nSize = this.size()
    return object : Iterator {
        var i = 0
        override fun hasNext(): Boolean = i < nSize
        override fun next(): Long = keyAt(i++)
    }
}

fun  LongSparseArray.entriesIterator(): Iterator> {
    val nSize = this.size()
    return object : Iterator> {
        var i = 0
        override fun hasNext(): Boolean = i < nSize
        override fun next() = Pair(keyAt(i), valueAt(i++))
    }
}

You can also convert to a list, if you wish. Example:

sparseArray.keysIterator().asSequence().toList()

I think it might even be safe to delete items using remove on the LongSparseArray itself (not on the iterator), as it is in ascending order.

---

EDIT: Seems there is even an easier way, by using collection-ktx (example here) . It's implemented in a very similar way to what I wrote, actally.

Gradle requires this:

implementation 'androidx.core:core-ktx:#'
implementation 'androidx.collection:collection-ktx:#'

Here's the usage for LongSparseArray :

    val sparse= LongSparseArray()
    for (key in sparse.keyIterator()) {
    }
    for (value in sparse.valueIterator()) {
    }
    sparse.forEach { key, value -> 
    }

And for those that use Java, you can use LongSparseArrayKt.keyIterator , LongSparseArrayKt.valueIterator and LongSparseArrayKt.forEach , for example. Same for the other cases.