What s the best way to iterate an Android Cursor

Question

I frequently see code which involves iterating over the result of a database query  doing something with each row  and then moving on to the next row  Typical examples are as follows    Cursor cursor   db rawQuery       cursor moveToFirst    while  cursor isAfterLast      false                 cursor moveToNext          Cursor cursor   db rawQuery       for  boolean hasItem   cursor moveToFirst          hasItem        hasItem   cursor moveToNext                    Cursor cursor   db rawQuery       if  cursor moveToFirst          do                                      while  cursor moveToNext         These all seem excessively long-winded to me  each with multiple calls to Cursor methods  Surely there must be a neater way

User · Answer

import java util Iterator  import android database Cursor   public class IterableCursor implements Iterable lt Cursor gt   Iterator lt Cursor gt        Cursor cursor      int toVisit      public IterableCursor Cursor cursor            this cursor   cursor          toVisit   cursor getCount              public Iterator lt Cursor gt  iterator             cursor moveToPosition -1           return this            public boolean hasNext             return toVisit gt 0            public Cursor next             if   hasNext                  throw new NoSuchElementException                      cursor moveToNext            toVisit--          return cursor            public void remove             throw new UnsupportedOperationException              Example code   static void listAllPhones Context context        Cursor phones   context getContentResolver   query ContactsContract CommonDataKinds Phone CONTENT URI  null  null  null  null       for  Cursor phone   new IterableCursor phones             String name   phone getString phone getColumnIndex ContactsContract CommonDataKinds Phone DISPLAY NAME            String phoneNumber   phone getString phone getColumnIndex ContactsContract CommonDataKinds Phone NUMBER            Log d  name     name     phoneNumber     phoneNumber             phones close

User · Answer

I d just like to point out a third alternative which also works if the cursor is not at the start position   if  cursor moveToFirst          do              do what you need with the cursor here       while  cursor moveToNext

User · Answer

Below could be the better way   if  cursor moveToFirst         while   cursor isAfterLast                 your code to implement          cursor moveToNext            cursor close      The above code would insure that it would go through entire iteration and won t escape first and last iteration

User · Answer

The best looking way I ve found to go through a cursor is the following   Cursor cursor        fill the cursor here  for  cursor moveToFirst     cursor isAfterLast    cursor moveToNext             do what you need with the cursor here     Don t forget to close the cursor afterwards  EDIT  The given solution is great if you ever need to iterate a cursor that you are not responsible of  A good example would be  if you are taking a cursor as argument in a method  and you need to scan the cursor for a given value  without having to worry about the cursor s current position

User · Answer

The cursor is the Interface that represents a 2-dimensional table of any database    When you try to retrieve some data using SELECT statement  then the database will 1st create a CURSOR object and return its reference to you   The pointer of this returned reference is pointing to the 0th location which is otherwise called as before the first location of the Cursor  so when you want to retrieve data from the cursor  you have to 1st move to the 1st record so we have to use moveToFirst  When you invoke moveToFirst   method on the Cursor  it takes the cursor pointer to the 1st location  Now you can access the data present in the 1st record  The best way to look    Cursor cursor  for  cursor moveToFirst           cursor isAfterLast           cursor moveToNext

User · Answer

The simplest way is this   while  cursor moveToNext                  The cursor starts before the first result row  so on the first iteration this moves to the first result if it exists  If the cursor is empty  or the last row has already been processed  then the loop exits neatly   Of course  don t forget to close the cursor once you re done with it  preferably in a finally clause    Cursor cursor   db rawQuery       try       while  cursor moveToNext                          finally       cursor close        If you target API 19   you can use try-with-resources   try  Cursor cursor   db rawQuery             while  cursor moveToNext

User · Answer

How about using foreach loop   Cursor cursor  for  Cursor c   CursorUtils iterate cursor           c doSth       However my version of CursorUtils should be less ugly  but it automatically closes the cursor   public class CursorUtils   public static Iterable lt Cursor gt  iterate Cursor cursor        return new IterableWithObject lt Cursor gt  cursor             Override         public Iterator lt Cursor gt  iterator                 return new IteratorWithObject lt Cursor gt  t                     Override                 public boolean hasNext                         t moveToNext                        if  t isAfterLast                              t close                            return false                                            return true                                     Override                 public Cursor next                         return t                                     Override                 public void remove                         throw new UnsupportedOperationException  CursorUtils   remove                                          Override                 protected void onCreate                         t moveToPosition -1                                                        private static abstract class IteratorWithObject lt T gt  implements Iterator lt T gt        protected T t      public IteratorWithObject T t            this t   t          this onCreate              protected abstract void onCreate       private static abstract class IterableWithObject lt T gt  implements Iterable lt T gt        protected T t      public IterableWithObject T t            this t   t

User · Answer

Initially  cursor is not on the first row show using moveToNext   you can iterate the cursor when record is not exist then it return false unless it return true   while  cursor moveToNext

User · Answer

The Do While solution is more elegant  but if you do use just the While solution posted above  without the moveToPosition -1  you will miss the first element  at least on the Contact query    I suggest    if  cursor getCount    gt  0        cursor moveToPosition -1       while  cursor moveToNext                 lt do stuff gt

User · Answer

if  cursor getCount      0    return   cursor moveToFirst     while   cursor isAfterLast           do something   cursor moveToNext       cursor close

[android] What's the best way to iterate an Android Cursor?

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