List

public final class List<T: Object>: ListBase

List is the container type in Realm used to define to-many relationships.

Like Swift’s Array, List is a generic type that is parameterized on the type of Object it stores.

Unlike Swift’s native collections, Lists are reference types, and are only immutable if the Realm that manages them is opened as read-only.

Lists can be filtered and sorted with the same predicates as Results<T>.

Properties of List type defined on Object subclasses must be declared as let and cannot be dynamic.

  • Returns the object at the given index (get), or replaces the object at the given index (set).

    Warning

    You can only set an object during a write transaction.

    Declaration

    Swift

    public subscript(position: Int) -> T

    Parameters

    index

    The index of the object to retrieve or replace.

  • The type of the elements contained within the collection.

    Declaration

    Swift

    public typealias Element = T
  • The Realm which manages the list, or nil if the list is unmanaged.

    Declaration

    Swift

    public var realm: Realm?
  • Indicates if the list can no longer be accessed.

    Declaration

    Swift

    public var isInvalidated: Bool
  • Creates a List that holds Realm model objects of type T.

    Declaration

    Swift

    public override init()
  • Returns the index of an object in the list, or nil if the object is not present.

    Declaration

    Swift

    public func index(of object: T) -> Int?

    Parameters

    object

    An object to find.

  • Returns the index of the first object in the list matching the predicate, or nil if no objects match.

    Declaration

    Swift

    public func index(matching predicate: NSPredicate) -> Int?

    Parameters

    predicate

    The predicate with which to filter the objects.

  • Returns the index of the first object in the list matching the predicate, or nil if no objects match.

    Declaration

    Swift

    public func index(matching predicateFormat: String, _ args: Any...) -> Int?

    Parameters

    predicateFormat

    A predicate format string, optionally followed by a variable number of arguments.

  • Returns the first object in the list, or nil if the list is empty.

    Declaration

    Swift

    public var first: T?
  • Returns the last object in the list, or nil if the list is empty.

    Declaration

    Swift

    public var last: T?
  • Returns an Array containing the results of invoking valueForKey(_:) using key on each of the collection’s objects.

    Declaration

    Swift

    public override func value(forKey key: String) -> Any?
  • Returns an Array containing the results of invoking valueForKeyPath(_:) using keyPath on each of the collection’s objects.

    Declaration

    Swift

    public override func value(forKeyPath keyPath: String) -> Any?

    Parameters

    keyPath

    The key path to the property whose values are desired.

  • Invokes setValue(_:forKey:) on each of the collection’s objects using the specified value and key.

    Warning

    This method can only be called during a write transaction.

    Declaration

    Swift

    public override func setValue(_ value: Any?, forKey key: String)

    Parameters

    value

    The object value.

    key

    The name of the property whose value should be set on each object.

  • Returns a Results containing all objects matching the given predicate in the list.

    Declaration

    Swift

    public func filter(_ predicateFormat: String, _ args: Any...) -> Results<T>

    Parameters

    predicateFormat

    A predicate format string, optionally followed by a variable number of arguments.

  • Returns a Results containing all objects matching the given predicate in the list.

    Declaration

    Swift

    public func filter(_ predicate: NSPredicate) -> Results<T>

    Parameters

    predicate

    The predicate with which to filter the objects.

  • Returns a Results containing the objects in the list, but sorted.

    Objects are sorted based on the values of the given property. For example, to sort a list of Students from youngest to oldest based on their age property, you might call students.sorted(byProperty: "age", ascending: true).

    Warning

    Lists may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.

    Declaration

    Swift

    public func sorted(byProperty property: String, ascending: Bool = true) -> Results<T>

    Parameters

    property

    The name of the property to sort by.

    ascending

    The direction to sort in.

  • Returns a Results containing the objects in the list, but sorted.

    Warning

    Lists may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.

    Declaration

    Swift

    public func sorted<S: Sequence>(by sortDescriptors: S) -> Results<T> where S.Iterator.Element == SortDescriptor
  • Returns the minimum (lowest) value of the given property among all the objects in the list, or nil if the list is empty.

    Warning

    Only a property whose type conforms to the MinMaxType protocol can be specified.

    Declaration

    Swift

    public func min<U: MinMaxType>(ofProperty property: String) -> U?

    Parameters

    property

    The name of a property whose minimum value is desired.

  • Returns the maximum (highest) value of the given property among all the objects in the list, or nil if the list is empty.

    Warning

    Only a property whose type conforms to the MinMaxType protocol can be specified.

    Declaration

    Swift

    public func max<U: MinMaxType>(ofProperty property: String) -> U?

    Parameters

    property

    The name of a property whose maximum value is desired.

  • Returns the sum of the values of a given property over all the objects in the list.

    Warning

    Only a property whose type conforms to the AddableType protocol can be specified.

    Declaration

    Swift

    public func sum<U: AddableType>(ofProperty property: String) -> U

    Parameters

    property

    The name of a property whose values should be summed.

  • Returns the average value of a given property over all the objects in the list, or nil if the list is empty.

    Warning

    Only a property whose type conforms to the AddableType protocol can be specified.

    Declaration

    Swift

    public func average<U: AddableType>(ofProperty property: String) -> U?

    Parameters

    property

    The name of a property whose average value should be calculated.

  • Appends the given object to the end of the list.

    If the object is managed by a different Realm than the receiver, a copy is made and added to the Realm managing the receiver.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Swift

    public func append(_ object: T)

    Parameters

    object

    An object.

  • Appends the objects in the given sequence to the end of the list.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Swift

    public func append<S: Sequence>(objectsIn objects: S) where S.Iterator.Element == T
  • Inserts an object at the given index.

    Warning

    This method may only be called during a write transaction.

    Warning

    This method will throw an exception if called with an invalid index.

    Declaration

    Swift

    public func insert(_ object: T, at index: Int)

    Parameters

    object

    An object.

    index

    The index at which to insert the object.

  • Removes an object at the given index. The object is not removed from the Realm that manages it.

    Warning

    This method may only be called during a write transaction.

    Warning

    This method will throw an exception if called with an invalid index.

    Declaration

    Swift

    public func remove(objectAtIndex index: Int)

    Parameters

    index

    The index at which to remove the object.

  • Removes the last object in the list. The object is not removed from the Realm that manages it.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Swift

    public func removeLast()
  • Removes all objects from the list. The objects are not removed from the Realm that manages them.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Swift

    public func removeAll()
  • Replaces an object at the given index with a new object.

    Warning

    This method may only be called during a write transaction.

    Warning

    This method will throw an exception if called with an invalid index.

    Declaration

    Swift

    public func replace(index: Int, object: T)

    Parameters

    index

    The index of the object to be replaced.

    object

    An object.

  • Moves the object at the given source index to the given destination index.

    Warning

    This method may only be called during a write transaction.

    Warning

    This method will throw an exception if called with invalid indices.

    Declaration

    Swift

    public func move(from: Int, to: Int)

    Parameters

    from

    The index of the object to be moved.

    to

    index to which the object at from should be moved.

  • Exchanges the objects in the list at given indices.

    Warning

    This method may only be called during a write transaction.

    Warning

    This method will throw an exception if called with invalid indices.

    Declaration

    Swift

    public func swap(index1: Int, _ index2: Int)

    Parameters

    index1

    The index of the object which should replace the object at index index2.

    index2

    The index of the object which should replace the object at index index1.

  • Registers a block to be called each time the collection changes.

    The block will be asynchronously called with the initial results, and then called again after each write transaction which changes either any of the objects in the collection, or which objects are in the collection.

    The change parameter that is passed to the block reports, in the form of indices within the collection, which of the objects were added, removed, or modified during each write transaction. See the RealmCollectionChange documentation for more information on the change information supplied and an example of how to use it to update a UITableView.

    At the time when the block is called, the collection will be fully evaluated and up-to-date, and as long as you do not perform a write transaction on the same thread or explicitly call realm.refresh(), accessing it will never perform blocking work.

    Notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. When notifications can’t be delivered instantly, multiple notifications may be coalesced into a single notification. This can include the notification with the initial collection.

    For example, the following code performs a write transaction immediately after adding the notification block, so there is no opportunity for the initial notification to be delivered first. As a result, the initial notification will reflect the state of the Realm after the write transaction.

    let results = realm.objects(Dog.self)
    print("dogs.count: \(dogs?.count)") // => 0
    let token = dogs.addNotificationBlock { changes in
        switch changes {
        case .initial(let dogs):
            // Will print "dogs.count: 1"
            print("dogs.count: \(dogs.count)")
            break
        case .update:
            // Will not be hit in this example
            break
        case .error:
            break
        }
    }
    try! realm.write {
        let dog = Dog()
        dog.name = "Rex"
        person.dogs.append(dog)
    }
    // end of run loop execution context
    

    You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call stop() on the token.

    Warning

    This method cannot be called during a write transaction, or when the containing Realm is read-only.

    Declaration

    Swift

    public func addNotificationBlock(_ block: @escaping (RealmCollectionChange<List>) -> Void) -> NotificationToken

    Parameters

    block

    The block to be called whenever a change occurs.

    Return Value

    A token which must be held for as long as you want updates to be delivered.

  • Replace the given subRange of elements with newElements.

    Declaration

    Swift

    public func replaceSubrange<C: Collection>(_ subrange: Range<Int>, with newElements: C)
            where C.Iterator.Element == T

    Parameters

    subRange

    The range of elements to be replaced.

    newElements

    The new elements to be inserted into the List.

  • The position of the first element in a non-empty collection. Identical to endIndex in an empty collection.

    Declaration

    Swift

    public var startIndex: Int
  • The collection’s past the end position. endIndex is not a valid argument to subscript, and is always reachable from startIndex by zero or more applications of successor().

    Declaration

    Swift

    public var endIndex: Int
  • The collection’s past the end position. endIndex is not a valid argument to subscript, and is always reachable from startIndex by zero or more applications of successor().

    Declaration

    Swift

    public func index(after i: Int) -> Int

    Parameters

    i

    A valid index of the collection. i must be less than endIndex.

    Return Value

    The index value immediately after i.

  • The collection’s past the end position. endIndex is not a valid argument to subscript, and is always reachable from startIndex by zero or more applications of successor().

    Declaration

    Swift

    public func index(before i: Int) -> Int

    Parameters

    i

    A valid index of the collection. i must be greater than startIndex.

    Return Value

    The index value immediately before i.