iOS SDK
Through Yorkie iOS SDK, you can efficiently build collaborative applications. On the client-side implementation, you can create Documents that are automatically synced with remote peers with minimal effort.
If you want to install the SDK, refer to the Getting Started with iOS SDK.
Client
Client
is a normal client that can communicate with the server. It has Documents and sends changes of the Document from local to the server to synchronize with other replicas remotely.
Creating a Client
We can create a Client using Client(rpcAddress: RPCAddress(host:,port:), options:)
. After the Client has been activated, it is connected to the server and ready to use.
let client = Client(rpcAddress: RPCAddress(host: "api.yorkie.dev", port: 443), options: ClientOptions(apiKey: "xxxxxxxxxxxxxxxxxxxx"))try await client.activate()
Subscribing to Client events
We can use client.eventStream
to subscribe to client-based events, such as status-changed
, stream-connection-status-changed
.
target.eventStream.sink { event inswitch event.type {case .statusChanged:()case .streamConnectionStatusChanged:()default:break}}
By using the value of the stream-connection-status-changed
event, it is possible to determine whether the Client is connected to the network.
If you want to know about other ClientEvents, please refer to the ClientEventType.
Document
Document
is a primary data type in Yorkie, which provides a JSON-like updating experience that makes it easy to represent your application's model.
A Document
can be updated without being attached to the client, and its changes are automatically propagated to other clients when the Document
is attached to the Client
or when the network is restored.
Creating a Document
We can create a Document using Document(key:)
. Let's create a Document with a key and attach it to the Client.
let doc = Document(key: "doc-1")
The document key is used to identify the Document in Yorkie. It is a string that can be freely defined by the user.
However, it is allowed to use only a-z
, A-Z
, 0-9
, -
, .
, _
, ~
and must be less than 120 characters.
Attaching the Document
When you attach, the client notifies the server that it is subscribing to this document. If the document does not exist on the server, it will be created, and any local changes that occurred will be updated to the server's document. If the server already has a document associated with the provided key, it sends the existing changes to the client, which are then applied to synchronize the document.
Once attached, the document becomes synchronized with other clients. This ensures that any modifications made by one client are instantly propagated to other clients collaborating on the same document.
The second and third arguments are belows.
initialPresence
(Optional): Sets the initial presence of the client that attaches the document. The presence is shared with other users participating in the document. It must be Codable.isRealtimeSync
(Optional): Specifies whether to enable real-time synchronization. The default value istrue
, which means synchronization occurs automatically. If set tofalse
, you should manually control the synchronization.
try await clientA.attach(doc, ["color: "blue", "cursor": ["x": 0, "y": 0]], true)
Updating presence
The Document.update()
method allows you to make changes to the state of the current user's presence.
Specific properties provided will be changed. The existing presence object will be updated by merging the new changes. In other words, properties not specified in the update function will remain unchanged.
try await doc.update { root, presence inpresence.set(["cursor": ["x": 1, "y": 1]])}// final state// presence = { color: 'blue', cursor: { x: 1, y: 1 } }// we can see that the changes made were merged and the final state of the current user's presence is as we desire
Note, the properties provided will be replaced entirely and not merely updated.
For example:
// let's say 'color' is a property of cursortry await client.attach(doc, ["cursor": ["x": 0, "y": 0, "color": "red"]])try await doc.update { root, presence in// we want to change the x y coordinates of our cursorpresence.set(["cursor": ["x": 1, "y": 1]])}// final state// presence = { cursor: { x: 1, y: 1 } }// we can see that all properties inside cursor get replaced (i.e. we lose the property 'color')
Getting presence
Document.getPresence(clientID)
It returns the presence of a specific client.
await doc.getPresence(client.id!) // ["color": "blue", "cursor": ["x": 1, "y": 1]]
Document.getMyPresence()
It returns the presence of the current client that has attached to the document.
await doc.getMyPresence() // ["color": "blue", "cursor": ["x": 1, "y": 1]]
Document.getPresences()
It returns an array about all clients currently participating in the document. Each entry in the array includes the client's id and presence.
let users = await doc.getPresences()for (clientID, presence) in users {// Do somethins}
Document.subscribePresence(.presence)
This method allows you to subscribe to all presence-related changes. By subscribing to these events, you can be notified when specific changes occur within the document, such as clients attaching, detaching, or modifying their presence.
await doc.subscribePresence { event inif event.type == .initialized {// Array of other users currently participating in the document// event.value;}if event.type == .watched {// A user has joined the document editing in online// event.value;}if event.type == .unwatched {// A user has left the document editing// event.value;}if event.type == .presenceChanged {// A user has updated their presence// event.value;}}
Document.subscribePresence(.myPresence)
This method is specifically for subscribing to changes in the presence of the current client that has attached to the document.
The possible event.type are: initialized
, presenceChanged
.
await doc.subscribePresence(.myPresence) { event in// Do something}
Document.subscribePresence(.others)
This method enables you to subscribe to changes in the presence of other clients participating in the document.
The possible event.type are: watched
, unwatched
, presenceChanged
.
await doc.subscribePresence(.others) { event inif event.type == .watched {addUser(event.value)}if event.type == .unwatched {removeUser(event.value)}if event.type == .presenceChanged {updateUser(event.value)}}
Editing the Document
Document.update(:,message:)
enables you to modify a Document. The optional message
allows you to add a description to the change. If the Document is attached to the Client, all changes are automatically synchronized with other Clients.
let message = "update document for test";try await doc.update({ root inroot.obj = [:] // {"obj":{}}let obj = root.obj as! JSONObjectobj.num = Int64(1) // {"obj":{"num":1}}obj.obj = ["str": "a"] // {"obj":{"num":1,"obj":{"str":"a"}}}obj.arr = [Int64(1), Int64(2)] // {"obj":{"num":1,"obj":{"str":"a"},"arr":[1,2]}}}, message: message);
Under the hood, root
in the update
function creates a change
, a set of operations, using a JavaScript proxy. Every element has its unique ID, created by the logical clock. This ID is used by Yorkie to track which object is which.
You can get the contents of the Document using doc.getRoot()
.
let root = doc.getRoot()print(root.obj!) // {"num":1,"obj":{"str":"a"},"arr":[1,2]}let obj = root.obj as! JSONObjectprint(obj.num!) // 1print(obj.obj!) // {"str":"a"}print(obj.arr!) // [1,2]
Subscribing to Document
Document.subscribe()
A Document can be modified by changes generated remotely or locally in Yorkie.
Whenever the Document is modified, change events are triggered and we can subscribe to these events using the document.subscribe(callback)
.
The callback is called with an event object, and the event.type
property indicates the source of the change, which can be one of the following values: localChange
, remoteChange
or snapshot
.
When the event.type
is localChange
or remoteChange
, the event.value
is a ChangeInfo, which has message
, operations
and actorID
properties.
For more information about changeInfo for document events, please refer to the ChangeInfo.
await self.doc.subscribe { event inif event.type == .localChange {print(event)} else if let event = event as? RemoteChangeEvent {let changeInfo = event.valuechangeInfo.operations.forEach { op inswitch (op.type) {case .increase:// Do something...breakdefault:break}}}}
Document.subscribe("$.path")
Additionally, you can subscribe to changes for a specific path in the Document using doc.subscribe(targetPath, callback)
with a path argument, such as $.todos
, where the $
sign indicates the root of the document.
The callback function is called when the target path and its nested values are changed.
With this feature, you can easily subscribe to changes for a specific part of the document and perform different actions based on the updated values.
await doc.subscribe("$.todos") { event in// The callback will be called when the root.todos or its nested values change.Task {let target = try? await target.getValueByPath(path: "$.todos") // You can get the value by path.}// Do something...}
Changing Synchronization Setting
To change the synchronization setting for a document, you can use client.pause(doc)
and client.resume(doc)
.
When you pause a document, the synchronization process will no longer occur in realtime, and you will need to manually execute the synchronization to ensure that the changes are propagated to other clients.
To resume the realtime synchronization, you can call client.resume(doc)
.
// 1. Pause real-time synctry await client.pause(doc)try await client.sync(doc) // To perform synchronization, you need to manually call the sync function// 2. Resume real-time synctry await client.resume(doc)
Changing Synchronization Mode
By default, Yorkie synchronizes a document in push-pull
mode, where local changes are pushed to the server, and remote changes are pulled from the server.
If you only want to send your changes and not receive remote changes, you can use push-only
mode.
For realtime synchronization, you can use client.pauseRemoteChanges(doc)
and client.resumeRemoteChanges(doc)
.
For manual synchronization, you can pass the desired sync mode to client.sync(doc, syncMode)
.
// Pause remote changes for realtime synctry await client.pauseRemoteChanges(doc)// Resume remote changes for realtime synctry await client.resumeRemoteChanges(doc)// Manual sync in Push-Only modetry await client.sync(doc, .pushOnly)// Manual sync in Push-Pull modetry await client.sync(doc, .pushPull)
Detaching the Document
If the document is no longer used, it should be detached to increase the efficiency of GC removing CRDT tombstones. For more information about GC, please refer to Garbage Collection.
try await client.detach(doc)
Custom CRDT types
Custom CRDT types are data types that can be used for special applications such as text editors and counters, unlike general JSON data types such as JSONObject
and JSONArray
. Custom CRDT types can be created in the callback function of document.update
.
JSONText
JSONText
provides supports for collaborative text editing. In addition, contents in JSONText
can have attributes; for example, characters can be bold, italic, or underlined.
try await doc.update{ root inroot.text = JSONText() // {"text":[]}(root.text as? JSONText)?.edit(0, 0, "hello") // {"text":[{"val":"hello"}]}(root.text as? JSONText)?.edit(0, 1, "H") // {"text":[{"val":"H"},{"val":"ello"}]}(root.text as? JSONText)?.setStyle(fromIdx: 0, toIdx: 1, attributes: ["bold": true]) // {"text":[{"attrs":{"bold":"true"},"val":"H"},{"val":"ello"}]}}
Selection using presence
The temporary client information, such as text selection, does not need to be stored in the document permanently.
Instead, it can be effectively shared using presence
.
When transmitting text selection information, it is essential to convert the index
, which can vary based on the text state, into the position
used by Yorkie.JSONText
.
This converted position selection can then be sent and applied through presence.
Here is an example where presence is used to share text selection between users in CodeMirror editor.
- When the text selection is changed:
let range: NSRange // eg. selected range converted from selectedTextRange of UITextViewlet fromIdx = range.locationlet toIdx = range.location + range.lengthtry await doc.update { root, presence inif let range = try? (root.content as? JSONText)?.indexRangeToPosRange((fromIdx, toIdx)) {presence.set(["from": range.0, "to": range.1])}}
- When applying other user's selection changes:
await doc.subscribePresence(.others) { event inif let event = event as? PresenceChangedEvent {if let fromPos: TextPosStruct = decodePresence(event.value["from"]),let toPos: TextPosStruct = decodePresence(event.value["to"]) {if let (fromIdx, toIdx) = try? await(document.getRoot().content as? JSONText)?.posRangeToIndexRange((fromPos, toPos)) {// Handle the updated selection in the editor}}}}private func decodePresence<T: Decodable>(_ dictionary: Any?) -> T? {guard let dictionary = dictionary as? [String: Any],let data = try? JSONSerialization.data(withJSONObject: dictionary, options: [])else {return nil}return try? JSONDecoder().decode(T.self, from: data)}
Text selection can be efficiently shared using presence. Please refer to the following example for a complete code:
An example of Text Editor: Text Editor example
JSONCounter
JSONCounter
supports integer types changing with addition and subtraction. If an integer data needs to be modified simultaneously, JSONCounter
should be used instead of primitives.
try await doc.update{ root inroot.counter = JSONCounter(value: Int64(1)) // {"counter":1}(root.counter as? JSONCounter<Int64>)?.increase(value: 2) // {"counter":3}(root.counter as? JSONCounter<Int64>)?.increase(value: 3) // {"counter":6}(root.counter as? JSONCounter<Int64>)?.increase(value: -4) // {"counter":2}}
Reference
For details on how to use the iOS SDK, please refer to iOS SDK Reference.