If we want to develop an application that allows data and files to be shared and synchronized between different devices, we will need to use a backend service that allows us to perform these tasks. In the case of devices with iOS, or macOS, we can use CloudKit. In this article we are going to see how a task application is developed with CloudKit.

What is CloudKit?

CloudKit is Apple’s storage service that allows your applications to save data and files remotely. Apple introduced CloudKit at WWDC 2014 as a new library that allowed communication with iCloud servers.

With CloudKit and Swift we can store any type of data and files for free up to 10 GB of file storage, 100 MB of database storage, 2 GB of data transfer and 40 requests per second. But we can achieve much greater capacity for free depending on the number of users added (1 PB of file storage, 10 TB of database, 200 TB of data transfer and 400 requests per second).

We can compare CloudKit with other BaaS (Backend as a Service) solutions, such as Firebase.

With CloudKit, Apple also offers:

  • An API to communicate and transfer data between devices and iCloud.
  • A desktop to manage data stored on Apple servers, measure user activity or bandwidth consumption.

Using CloudKit

To use CloudKit we must bear in mind that:

  • You must be registered in the iOS Developer Program to be able to use CloudKit.
  • Since the data is not saved locally, but on Apple servers, an application that uses CloudKit is not useful without an Internet connection.
  • User data is protected, as developers can only access their own databases and not private user data.
  • Apple recommends notifying the user if an error occurs (such as finding an error in the saving process), so that they know that data may have been lost or has not been saved.

CloudKit databases

To start working with CloudKit we must bear in mind that, in the same way that each application has its own sandbox, similarly each application has a container in iCloud (if we have registered the application for it, as we will see later). CloudKit defines three types of databases:

  • Private
  • Public
  • Shared

Private database

Each user of an application (if it has been registered to use iCloud) has a private database in an iCloud container, as long as the user is logged in to their iCloud account. Being private, developers cannot access the data stored in this database.

Public database

An iCloud container also contains a public database, but in this case its data can be read by all users of the application, even if they have not logged in with their iCloud account. Please note that since CloudKit logs always have an owner, only users who are logged into iCloud will be able to write data to the public database.

Shared database

In the same way as in the private database, the shared database is only accessible if you are logged into iCloud. It is used to share records from a user’s private database with other users of the application.

Concepts to consider

When working with CloudKit we have to take into account some concepts:

  • Container. These are instances of the CKContainer class that, as we have seen, store user data. We can access the application’s default container (default) or those that we have created:
  • Database. As we have seen, in CloudKit we can find three databases: public, private and shared. They are represented by objects of type CKDatabase.
  • Registry. They are objects of type CKRecord, and we can consider them as dictionaries in which the keys are the fields of the tables in the database.
  • Zone. They are represented by objects of the CKZone type, and it is the place where the data is saved. In CloudKit, all databases have a default zone, but we can also create custom zones, although only in private databases.

TodoList project

We are going to create a to-do list app, TodoList, which will be saved in iCloud. You can download this project from GitHub.

First of all we create a new project in Xcode with the Single View App template.

Creation of the TodoList project in Xcode 11.

Next, we enter the project data and select the Use Core Data and Use CloudKit options.

Selecting the Use Core Data and Use CloudKit options.

Now we must add the ability to the project to use iCloud. For this we select the application in Targets, then the Signing & Capabilities tab and, finally, the +Capability option. A menu will appear in which we will select the iCloud option.

We select iCloud capacity in the project.

CloudKit Dashboard

Now that we have created the project and the container, we have to create the records for the data that we will use in the application. We can do this from the CloudKit desktop, which will allow us to know how it works. For this we click on the CloudKit Dashboard button.

CloudKit Dashboard.

As seen in the image, the CloudKit desktop has six sections:

  • API Access. Manages API tokens and server-to-server keys that allow calls to the web service.
  • Data. Manages records and their types, indexes, subscriptions and security in public, private and shared databases.
  • Schema. In this section we find the options for Registration types, Indexes, Security roles and Subscription types.
  • Logs. Displays both historical and real-time data from server activity or notifications.
  • Telemetry. Displays graphs of server-side usage and performance in using databases, as well as notification events.
  • Usage. Displays information about active users, requests per second, or data storage.

Creating the database from the CloudKit Dashboard

As we have previously commented, we are going to create a simple application that will allow us to manage a list of tasks, which we will synchronize in iCloud. As this is a simple example, we will create a database with a table to save the tasks, with the following properties: title, creation date, modification date and whether it is done or not.

From the CloudKit Desktop, select Schema > Record Types > New Type, and give it the name of Task.

Adding the Task Registry Type.

Once this type of record is created, we select it and start adding fields (after adding them, click on Save):

  • title (of type String)
  • createdAt (of type Date)
  • modifiedAt (of type Date)
  • checked (of type Int64, since there are no booleans)
Creation of the different fields of Task.

The data can have any of the following basic types (you can also make arrays, List, of this data):

  • Asset. It is a file associated with a record, although it is stored independently (it has a limit of 1 MB).
  • Date/Time. A date and time data.
  • Int(64). It is a 64-bit integer.
  • Double. It is a double number.
  • Bytes. This is a byte buffer that is stored in the registry itself.
  • String. It is a text string.
  • Location. It is for geographic location data.
  • Reference. It is a reference to another table in order to create relationships between them.

Finally, we select Edit Indexes and add three:

  • createdAt of type SORTABLE (which will allow us to sort the results by creation date).
  • checked of type QUERYABLE (to find out whether the tasks are marked complete or not).
  • recordName of type QUERYABLE (to retrieve the records).

In this way we obtain the following image:

Final aspect of the scheme.

Adding sample data

Once the Task table has been created, we can add some sample data from the CloudKit Desktop. To do this, from the drop-down menu we select the Data option.

Selection of the Data option.

Next, in the left panel we select from the Database menu we select Public Database and, in the Zone menu, we select _defaultZone (it is the one that contains the public records of the application). Then, in the Type menu we select Task (table name) and then we click the New Record button to add data.

Adding records to the database.
Adding the data.

A little Swift

Once we have entered a couple of sample records, we are going to start developing a simple application. This project can be found in full on GitHub.

UI design

This project will basically consist of an UITableView component, which will be the one that shows the tasks. Each cell of this table will be a task with the title, the creation date and an icon to indicate if it has been done or not.

This table will be inside a UINavigationController component in the bar of which we will put the title and a button to add tasks. In this project, all this will be done through code, without using storyboards or .xib files.

UI design.

Project creation

To work without storyboards when establishing a project in Xcode 11 we have to do some steps after creating it:

  • We delete the file Main.storyboard.
  • In the General tab (TARGETS), we go to the Main interface selector and eliminate Main, leaving the field blank.
You have to delete Main and leave the field blank.

Finally, in the Info tab (TARGETS) we go to Application Scene Manifest > Scene Configuration > Application Session Role> Item 0 (Default Configuration) and delete the Storyboard Name field.

Deletion of the Storyboard Name field in the Info.plist file.

Since we will no longer call the Main.storyboard to start the project, we go to the SceneDelegate.swift file, and in the function scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) and replace its content with the following code:

This code creates a UINavigationController and adds the ViewController controller to it. Then assign it as rootViewController.

Create the record manager

Next we create a manager that will perform the tasks related to CloudKit (retrieve records, save them …). We are going to call it CloudKitManager.swift. First, we will add the functionality to retrieve iCloud logs.

In fetchTasks(completion: @escaping ([CKRecord] ?, FetchError) -> Void), the first thing we do is retrieve the container (of type CKContainer) of our application from the identifier we have given it (iCloud.com… ) and then we get the public database, which is where we have previously created the demo records.

Then we create a search (query, of type CKQuery) in which we indicate the name of the table that we have created in iCloud (Tasks), and we add a sorting criterion for the records that are obtained: in this case, it will order the records based on creation date (createdAt) from newest to oldest (ascending: false).

Next, we execute the query in the public database according to the publicDatabase.perform(<query: CKQuery, inZoneWith: CKRecordZone.ID?, completionHandler: ([CKRecord]?, Error?) -> Void>) method, in the that we introduce the query that we have created, the zone identifier (which is the default zone, default, and that is the one that we have selected when creating the table in iCloud).

When executing the query, we get a couple of parameters in response: a list of records [CKRecord] and an error (both cases are conditional, since they can have the value nil).

This response is processed in the processQueryResponseWith method, in which we check if there has been an error when performing the query, if any records have been returned and what these records are. To facilitate the handling of errors, enum FetchError has been created, which collects possible errors.

Creation of the UITableView component

The UITableView component will be simple, the only thing we will customize is that the cells can have a variable height, to show task titles of up to three lines (TasksTableViewController.swift):

We also create a custom cell (TaskCell.swift):

In which the toggleChecked() method allows you to change, for now, the status of the completed task icon.

Now in the ViewController.swift class we can already show the table and execute the iCloud call.

Records deletion

To delete records we will enable the use of cell dragging so that the option to delete appears. We will achieve this by adding the following method to the TasksTableViewController class:

We also modified this class to inject an instance of CloudKitManager.

And in the ViewController class we change the instance of the TasksTableViewController class, since now we will inject the CloudKitManager instance:

In CloudKitManager we add these methods to delete records and add the deletingError case to the FetchError enum:

And in the TasksTableViewController class we modify the last method:

Now we can test the deletion of tasks.

Deleting a record.

Adding a task

In order to create a task, we will create a UIViewController to which we will navigate by clicking on a ‘+’ button in the navigation bar. This new UIViewController, which we will call AddTaskController, will simply be made up of an UITextField component, in which we will introduce the task text, and a UIButton component, to add it.

In this code there are several important points:

  • The init method injects a CloudKitManager instance, in order to manage the addition of a record.
  • The method associated with the ‘Add task‘ button is called the addTask method of the CloudKitManager, which will manage the addition of new records. The code that is added for this case in CloudKitManager is (a new case, addingError, has also been added in the FetchError enum):
  • Finally, a protocol has been created to pass the created record to the ViewController. Finally, the starting controller (ViewController) is navigated.

In order to call the AddTaskController class we add a button to the navigation bar. We do this using the UIBarButtonItem component, to which we associate the addTask method. In this method we instantiate the controller, define the delegate and push the new controller.

Since we have defined the delegate for the ViewController, we have to make the ViewController adopt the methods of this protocol. We do this using a ViewController extension (to organize the code):

In this implementation of the addedTask method, any possible error would be handled and, in the event that everything is correct, the created record is sent to a new add(task: CKRecord) method that we will create in the TasksTableViewController class:

What this method does is add the new record to the beginning of the list of records (it is the newest) and then reload the data from the table.

Adding a new record.

Update a task

We have already seen how to recover, delete or create records with CloudKit. Now we will see how to update a registry in CloudKit. For this we will use a simple case, the one that corresponds to completing a task and marking it as completed.

First of all we add a new method in CloudKitManager:

When passing an object that already exists and saving it in CloudKit, its values are updated. To call this method when we mark the task complete, we create a protocol that allows passing the modified record from the cell to the TasksTableViewController class:

Now in the TasksTableViewController class we add the delegate to the cell:

And then we make the TasksTableViewController class adopt the protocol:

If we mark a record as complete and then turn off the app and reload it, we see that the record has been modified in iCloud.

Record update.


We have seen how we can create an application that uses CloudKit to synchronize data with iCloud. In this application we have integrated the basic CRUD methods (Create, Read, Update, Delete) of a database. Remember that you can download the complete project from GitHub.


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