ProjectedCollection

public struct ProjectedCollection<Element> : RandomAccessCollection, CustomStringConvertible, ThreadConfined where Element : RealmCollectionValue

ProjectedCollection is a special type of collection for Projection’s properties which should be used when you want to project a List of Realm Objects to a list of values. You don’t need to instantiate this type manually. Use it by calling projectTo on a List property:

class PersistedListObject: Object {
    @Persisted public var people: List<CommonPerson>
}

class ListProjection: Projection<PersistedListObject> {
    @Projected(\PersistedListObject.people.projectTo.firstName) var strings: ProjectedCollection<String>
}
  • Declaration

    Swift

    public typealias Index = Int
  • 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.

  • 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.

    If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. 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.

    class Person: Object {
        @Persisted var dogs: List<Dog>
    }
    class PersonProjection: Projection<Person> {
        @Projected(\Person.dogs.projectTo.name) var dogsNames: ProjectedCollection<String>
    }
    // ...
    let dogsNames = personProjection.dogsNames
    print("dogsNames.count: \(dogsNames?.count)") // => 0
    let token = dogsNames.observe { changes in
        switch changes {
        case .initial(let dogsNames):
            // Will print "dogsNames.count: 1"
            print("dogsNames.count: \(dogsNames.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 invalidate() 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 observe(on queue: DispatchQueue?,
                        _ block: @escaping (RealmCollectionChange<ProjectedCollection<Element>>) -> Void) -> NotificationToken

    Parameters

    queue

    The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.

    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.

  • 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.

    If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. 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.

    class Person: Object {
        @Persisted var dogs: List<Dog>
    }
    class PersonProjection: Projection<Person> {
        @Projected(\Person.dogs.projectTo.name) var dogNames: ProjectedCollection<String>
    }
    // ...
    let dogNames = personProjection.dogNames
    print("dogNames.count: \(dogNames?.count)") // => 0
    let token = dogs.observe { changes in
        switch changes {
        case .initial(let dogNames):
            // Will print "dogNames.count: 1"
            print("dogNames.count: \(dogNames.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
    

    If no key paths are given, the block will be executed on any insertion, modification, or deletion for all object properties and the properties of any nested, linked objects. If a key path or key paths are provided, then the block will be called for changes which occur only on the provided key paths. For example, if:

    class Person: Object {
        @Persisted var dogs: List<Dog>
    }
    class PersonProjection: Projection<Person> {
        @Projected(\Person.dogs.projectTo.name) var dogNames: ProjectedCollection<String>
    }
    // ...
    let dogNames = personProjection.dogNames
    let token = dogNames.observe(keyPaths: ["name"]) { changes in
        switch changes {
        case .initial(let dogNames):
           // ...
        case .update:
           // This case is hit:
           // - after the token is intialized
           // - when the name property of an object in the
           // collection is modified
           // - when an element is inserted or removed
           //   from the collection.
           // This block is not triggered:
           // - when a value other than name is modified on
           //   one of the elements.
        case .error:
            // ...
        }
    }
    // end of run loop execution context
    

    Changes to any other value that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would still trigger a notification.

    Note

    Multiple notification tokens on the same object which filter for separate key paths do not filter exclusively. If one key path change is satisfied for one notification token, then all notification token blocks for that object will execute.

    You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call invalidate() 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 observe(keyPaths: [String]? = nil, on queue: DispatchQueue? = nil,
                        _ block: @escaping (RealmCollectionChange<ProjectedCollection<Element>>) -> Void)
        -> NotificationToken

    Parameters

    keyPaths

    Only properties contained in the key paths array will trigger the block when they are modified. If nil, notifications will be delivered for any property change on the object. String key paths which do not correspond to a valid a property will throw an exception. See description above for more detail on linked properties.

    queue

    The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.

    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.

  • 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) -> Element { get set }

    Parameters

    index

    The index of the object to retrieve or replace.

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

    Declaration

    Swift

    public var startIndex: Int { get }
  • 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 { get }
  • The Realm which manages the object.

    Declaration

    Swift

    public var realm: Realm? { get }
  • Indicates if the collection can no longer be accessed.

    Declaration

    Swift

    public var isInvalidated: Bool { get }
  • A human-readable description of the object.

    Declaration

    Swift

    public var description: String { get }
  • Returns the index of an object in the linking objects, or nil if the object is not present.

    Declaration

    Swift

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

    Parameters

    object

    The object whose index is being queried.

  • Declaration

    Swift

    public var isFrozen: Bool { get }
  • Declaration

    Swift

    public func freeze() -> ProjectedCollection<Element>
  • Declaration

    Swift

    public func thaw() -> `Self`?