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

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For whoever is using Kotlin  honestly the by far easiest way to iterate over a SparseArray is  Use the Kotlin extension from Anko or Android KTX   credit to Yazazzello for pointing out Android KTX   Simply call forEach   i  item - gt

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Ooor you just create your own ListIterator   public final class SparseArrayIterator lt E gt  implements ListIterator lt E gt     private final SparseArray lt E gt  array  private int cursor  private boolean cursorNowhere           param array               to iterate over      return A ListIterator on the elements of the SparseArray  The elements            are iterated in the same order as they occur in the SparseArray               link  nextIndex    and   link  previousIndex    return a            SparseArray key  not an index  To get the index  call              link android util SparseArray indexOfKey int        public static  lt E gt  ListIterator lt E gt  iterate SparseArray lt E gt  array        return iterateAt array  -1              param array               to iterate over      param key               to start the iteration at    link android util SparseArray indexOfKey int                  lt  0 results in the same call as   link  iterate android util SparseArray        return A ListIterator on the elements of the SparseArray  The elements            are iterated in the same order as they occur in the SparseArray               link  nextIndex    and   link  previousIndex    return a            SparseArray key  not an index  To get the index  call              link android util SparseArray indexOfKey int        public static  lt E gt  ListIterator lt E gt  iterateAtKey SparseArray lt E gt  array  int key        return iterateAt array  array indexOfKey key               param array               to iterate over      param location               to start the iteration at  Value  lt  0 results in the same call               as   link  iterate android util SparseArray    Value  gt                  link android util SparseArray size    set to that size      return A ListIterator on the elements of the SparseArray  The elements            are iterated in the same order as they occur in the SparseArray               link  nextIndex    and   link  previousIndex    return a            SparseArray key  not an index  To get the index  call              link android util SparseArray indexOfKey int        public static  lt E gt  ListIterator lt E gt  iterateAt SparseArray lt E gt  array  int location        return new SparseArrayIterator lt E gt  array  location      private SparseArrayIterator SparseArray lt E gt  array  int location        this array   array      if  location  lt  0            cursor   -1          cursorNowhere   true        else if  location  lt  array size              cursor   location          cursorNowhere   false        else           cursor   array size   - 1          cursorNowhere   true            Override public boolean hasNext         return cursor  lt  array size   - 1      Override public boolean hasPrevious         return cursorNowhere  amp  amp  cursor  gt   0    cursor  gt  0      Override public int nextIndex         if  hasNext              return array keyAt cursor   1         else           throw new NoSuchElementException              Override public int previousIndex         if  hasPrevious              if  cursorNowhere                return array keyAt cursor             else               return array keyAt cursor - 1                   else           throw new NoSuchElementException              Override public E next         if  hasNext              if  cursorNowhere                cursorNowhere   false                    cursor            return array valueAt cursor         else           throw new NoSuchElementException              Override public E previous         if  hasPrevious              if  cursorNowhere                cursorNowhere   false            else               cursor--                    return array valueAt cursor         else           throw new NoSuchElementException              Override public void add E object        throw new UnsupportedOperationException        Override public void remove         if   cursorNowhere            array remove array keyAt cursor            cursorNowhere   true          cursor--        else           throw new IllegalStateException              Override public void set E object        if   cursorNowhere            array setValueAt cursor  object         else           throw new IllegalStateException

User · Answer

Here is simple Iterator lt T gt  and Iterable lt T gt  implementations for SparseArray lt T gt    public class SparseArrayIterator lt T gt  implements Iterator lt T gt        private final SparseArray lt T gt  array      private int index       public SparseArrayIterator SparseArray lt T gt  array            this array   array              Override     public boolean hasNext             return array size    gt  index              Override     public T next             return array valueAt index                 Override     public void remove             array removeAt index             public class SparseArrayIterable lt T gt  implements Iterable lt T gt        private final SparseArray lt T gt  sparseArray       public SparseArrayIterable SparseArray lt T gt  sparseArray            this sparseArray   sparseArray              Override     public Iterator lt T gt  iterator             return new SparseArrayIterator lt  gt  sparseArray             If you want to iterate not only a value but also a key   public class SparseKeyValue lt T gt        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 lt T gt  implements Iterator lt SparseKeyValue lt T gt  gt        private final SparseArray lt T gt  array      private int index       public SparseArrayKeyValueIterator SparseArray lt T gt  array            this array   array              Override     public boolean hasNext             return array size    gt  index              Override     public SparseKeyValue lt T gt  next             SparseKeyValue lt T gt  keyValue   new SparseKeyValue lt  gt  array keyAt index   array valueAt index            index            return keyValue              Override     public void remove             array removeAt index             public class SparseArrayKeyValueIterable lt T gt  implements Iterable lt SparseKeyValue lt T gt  gt        private final SparseArray lt T gt  sparseArray       public SparseArrayKeyValueIterable SparseArray lt T gt  sparseArray            this sparseArray   sparseArray              Override     public Iterator lt SparseKeyValue lt T gt  gt  iterator             return new SparseArrayKeyValueIterator lt T gt  sparseArray             It s useful to create utility methods that return Iterable lt T gt  and Iterable lt SparseKeyValue lt T gt  gt    public abstract class SparseArrayUtils       public static  lt T gt  Iterable lt SparseKeyValue lt T gt  gt  keyValueIterable SparseArray lt T gt  sparseArray            return new SparseArrayKeyValueIterable lt  gt  sparseArray              public static  lt T gt  Iterable lt T gt  iterable SparseArray lt T gt  sparseArray            return new SparseArrayIterable lt  gt  sparseArray             Now you can iterate SparseArray lt T gt    SparseArray lt String gt  a         for  String s  SparseArrayUtils iterable a                  for  SparseKeyValue lt String gt  s  SparseArrayUtils keyValueIterable a

User · Answer

Seems I found the solution  I hadn t properly noticed the keyAt index  function   So I ll go with something like this   for int i   0  i  lt  sparseArray size    i         int key   sparseArray keyAt i         get the object by the key     Object obj   sparseArray get key

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For removing all the elements from SparseArray using the above looping leads to Exception   To avoid this Follow the below code to remove all the elements from SparseArray using normal loops  private void getValues              for int i 0  i lt sparseArray size    i               int key   sparseArray keyAt i             Log d  Element at   key    is   sparseArray get key              sparseArray remove key             i -1

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The accepted answer has some holes in it  The beauty of the SparseArray is that it allows gaps in the indeces  So  we could have two maps like so  in a SparseArray      0 true   250 true    Notice the size here would be 2  If we iterate over size  we will only get values for the values mapped to index 0 and index 1  So the mapping with a key of 250 is not accessed    for int i   0  i  lt  sparseArray size    i         int key   sparseArray keyAt i         get the object by the key     Object obj   sparseArray get key       The best way to do this is to iterate over the size of your data set  then check those indeces with a get   on the array  Here is an example with an adapter where I am allowing batch delete of items   for  int index   0  index  lt  mAdapter getItemCount    index           if  toDelete get index     true            long idOfItemToDelete    allItems get index  getId             mDbManager markItemForDeletion idOfItemToDelete                     I think ideally the SparseArray family would have a getKeys   method  but alas it does not

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If you don t care about the keys  then valueAt int  can be used to while iterating through the sparse array to access the values directly   for int i   0  nsize   sparseArray size    i  lt  nsize  i          Object obj   sparseArray valueAt i

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If you use Kotlin  you can use extension functions as such  for example   fun  lt T gt  LongSparseArray lt T gt  valuesIterator    Iterator lt T gt        val nSize   this size       return object   Iterator lt T gt            var i   0         override fun hasNext    Boolean   i  lt  nSize         override fun next    T   valueAt i             fun  lt T gt  LongSparseArray lt T gt  keysIterator    Iterator lt Long gt        val nSize   this size       return object   Iterator lt Long gt            var i   0         override fun hasNext    Boolean   i  lt  nSize         override fun next    Long   keyAt i             fun  lt T gt  LongSparseArray lt T gt  entriesIterator    Iterator lt Pair lt Long  T gt  gt        val nSize   this size       return object   Iterator lt Pair lt Long  T gt  gt            var i   0         override fun hasNext    Boolean   i  lt  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 lt String gt        for  key in sparse keyIterator                for  value in sparse valueIterator                sparse forEach   key  value - gt           And for those that use Java  you can use LongSparseArrayKt keyIterator   LongSparseArrayKt valueIterator and LongSparseArrayKt forEach   for example  Same for the other cases

User · Answer

The answer is no because SparseArray doesn t provide it  As pst put it  this thing doesn t provide any interfaces   You could loop from 0 - size   and skip values that return null  but that is about it   As I state in my comment  if you need to iterate use a Map instead of a SparseArray  For example  use a TreeMap which iterates in order by the key   TreeMap lt Integer  MyType gt

User · Answer

Simple as Pie  Just make sure you fetch array size before actually performing the loop   for int i   0  arraySize  mySparseArray size    i  lt  arraySize  i         Object obj   mySparseArray get    int key      mySparseArray keyAt i        Hope this helps

[java] How to iterate through SparseArray?

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