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

Here is simple Iterator and Iterable implementations for SparseArray:

public class SparseArrayIterator implements Iterator {
    private final SparseArray array;
    private int index;

    public SparseArrayIterator(SparseArray array) {
        this.array = array;
    }

    @Override
    public boolean hasNext() {
        return array.size() > index;
    }

    @Override
    public T next() {
        return array.valueAt(index++);
    }

    @Override
    public void remove() {
        array.removeAt(index);
    }

}

public class SparseArrayIterable implements Iterable {
    private final SparseArray sparseArray;

    public SparseArrayIterable(SparseArray sparseArray) {
        this.sparseArray = sparseArray;
    }

    @Override
    public Iterator iterator() {
        return new SparseArrayIterator<>(sparseArray);
    }
}

If you want to iterate not only a value but also a key:

public class SparseKeyValue {
    private final int key;
    private final T value;

    public SparseKeyValue(int key, T value) {
        this.key = key;
        this.value = value;
    }

    public int getKey() {
        return key;
    }

    public T getValue() {
        return value;
    }
}

public class SparseArrayKeyValueIterator implements Iterator> {
    private final SparseArray array;
    private int index;

    public SparseArrayKeyValueIterator(SparseArray array) {
        this.array = array;
    }

    @Override
    public boolean hasNext() {
        return array.size() > index;
    }

    @Override
    public SparseKeyValue next() {
        SparseKeyValue keyValue = new SparseKeyValue<>(array.keyAt(index), array.valueAt(index));
        index++;
        return keyValue;
    }

    @Override
    public void remove() {
        array.removeAt(index);
    }

}

public class SparseArrayKeyValueIterable implements Iterable> {
    private final SparseArray sparseArray;

    public SparseArrayKeyValueIterable(SparseArray sparseArray) {
        this.sparseArray = sparseArray;
    }

    @Override
    public Iterator> iterator() {
        return new SparseArrayKeyValueIterator(sparseArray);
    }
}

It's useful to create utility methods that return Iterable and Iterable>:

public abstract class SparseArrayUtils {
    public static  Iterable> keyValueIterable(SparseArray sparseArray) {
        return new SparseArrayKeyValueIterable<>(sparseArray);
    }

    public static  Iterable iterable(SparseArray sparseArray) {
        return new SparseArrayIterable<>(sparseArray);
    }
}

Now you can iterate SparseArray:

SparseArray a = ...;

for (String s: SparseArrayUtils.iterable(a)) {
   // ...
}

for (SparseKeyValue s: SparseArrayUtils.keyValueIterable(a)) {
  // ...
}