Home > Articles > Mobile Application Development & Programming

The iOS 5 Developer's Cookbook: iCloud Basics

This chapter introduces iCloud, shows you how it works, introduces the key classes you’ll use, and walks you through several recipes and code snippets that show you how to use it in your own projects.
This chapter is from the book

Ready to emerge from the confines of a single device or desktop system? Welcome to iCloud. iCloud lets you share data beyond the limitations of individual hardware and into a central data-storage hub. With iCloud, your applications can access and update shared documents without explicit synchronization. Changes on one unit propagate out to all other registered systems, updating when that hardware next accesses the Internet. This completely passive coordination is yours for free via iCloud. All you need to do is set up some entitlements and incorporate its features in your applications. It’s surprisingly easy to use. This chapter introduces iCloud, shows you how it works, introduces the key classes you’ll use, and walks you through several recipes and code snippets that show you how to use it in your own projects.

Setting Up an iCloud-Compatible Project

To get started on your first iCloud project, you add a simple entitlement. Open the Project > TARGETS > Entitlements pane and check the Enable Entitlements box shown in Figure 18-1. This option builds a new entitlement file, adding a trio of entitlement types. These types include iCloud containers (the shared folders where you can add and read data), iCloud Key-Value Store (enabling a shared dictionary look-up system), and Keychain Access Groups (allowing secure-item sharing between applications).

Figure 18-1

Figure 18-1 Enable iCloud functionality by establishing entitlements for your application. You can use the + button to add additional containers to your application. The first-listed container, which you can see defaults to the application identifier, acts as the default ubiquitous store.

Although Apple briefly flirted with enabling iCloud access on an application-by-application basis during the iOS 5 beta period, it eventually decided to enable iCloud for all applications without special provisioning. Any application identifier added to the provisioning portal is automatically enabled with iCloud access. This decision means that when you check the Entitlements box, you’ve done everything needed to get started with iCloud.

Determining Your Team Identifier Prefix

Every cloud application uses a special internal prefix—and it’s not the one you’re probably thinking of, the one associated with application identifiers at the provisioning portal. iCloud service uses your developer identifier (the “Team Identifier Prefix”) to enable you to write to and access cloud-based data. This identifier is associated with your account and listed in the iOS Member Center in the Your Account page as your organization or individual ID.

You can look this identifier up by visiting developer.apple.com/ios, and clicking Member Center. Sign in with your developer credentials and view the Your Account tab. The Program Membership section lists the identifier between the account name and account type entries.

Outside of visiting the developer site, the easiest way to locate the prefix you’re looking for is to take a peek into your Team Provisioning Profile. Use the Organizer > Devices > Provisioning Profiles pane to locate the provision file. Right-click iOS Team Provisioning Profile and choose Reveal Profile in Finder. Open this file in TextEdit and search for the TeamIdentifier key. It should appear exactly once in the file. Directly below the key , you will find a single-value, which is your team identifier prefix.

<key>TeamIdentifier</key>
<array>
    <string>YOURIDENTIFIER</string>
</array>

Containers

This team identifier prefix is used for all shared iCloud data containers. You can see this prefix in action by examining the default ubiquity folder for your application. Consider the following call. When passed nil as an argument, it looks up the default ubiquitous (i.e., iCloud) container URL. The default container is always the first item listed in the com.apple.developer.ubiquity-container-identifiers entitlement.

NSURL *ubiquity = [[NSFileManager defaultManager]
    URLForUbiquityContainerIdentifier:nil];
NSLog(@"Ubiquity: %@", ubiquity);

When executed, this code prints out the path to that container. The path includes a tilda-escaped version of the application identifier, complete with a team identifier prefix. The identifier ensures that containers are unique to each developer.

2011-08-29 12:17:41.094 HelloWorld[8069:707] Ubiquity:
file://localhost/private/var/mobile/Library/Mobile%20Documents/YOURTEAMIDENTIFIER~com~sadun~HelloWorld/

The default value added to the initial entitlement includes just one container, associated with the application identifier of the current project.

<key>com.apple.developer.ubiquity-container-identifiers</key>
<array>
    <string>$(TeamIdentifierPrefix)com.sadun.HelloWorld</string>
</array>

You can extend this entitlement to add more identifiers, so long as those items are associated with your team prefix, e.g.

<key>com.apple.developer.ubiquity-container-identifiers</key>
<array>
    <string>$(TeamIdentifierPrefix)com.sadun.HelloWorld</string>
    <string>$(TeamIdentifierPrefix)com.sadun.AnotherApp</string>
    <string>$(TeamIdentifierPrefix)com.sadun.SharedStorage</string>
</array>

Adding more identifiers enables you to add cross-application document sharing for any application built by the same developer account. Adding, for example, com.sadun.AnotherApp to these entitlements allows the HelloWorld application to access the AnotherApp application’s default container.

The reverse domain-name identifiers do not have to be tied to a specific application. Although the entitlement domains default to the application name (com.sadun.HelloWorld), you can add shared items or replace the default container with a shared name (e.g., com.sadun.SharedStorage).

Retrieving Identifiers in Code

Your team prefix plays an important role in iCloud development. Outside of the default container (the first entitlement item), which you can access by passing nil to the ubiquity URL query, you cannot access other containers without your team identifier prefix. You can hard code the prefix as a string constant, or you can retrieve the prefix with a simple method call. This method extracts the prefix for you:

+ (NSString *) teamPrefix
{
    NSURL *ubiquity = [[NSFileManager defaultManager]
        URLForUbiquityContainerIdentifier:nil];
    if (!ubiquity) return nil;
    NSArray *elements = [[ubiquity.path lastPathComponent]
        componentsSeparatedByString:@"~"];
    if (!elements.count) return nil;
    return [elements objectAtIndex:0];
}

Once extracted, you can create a valid container identifier by combining the prefix to a container name string (e.g., MYPREFIX.com.sadun.SharedStorage).

+ (NSString *) containerize: (NSString *) anIdentifier
{
    NSString *prefix = [self teamPrefix];
    if (!prefix) return nil;
    return [NSString stringWithFormat:@"%@.%@", prefix, anIdentifier];
}

Calls to URLForUbiquityContainerIdentifier: should not return nil. If they do, go through the following checklist:

  • Did you add an entitlement for the container identifier?
  • Did you use the proper team id prefix in the identifier?
  • Did you enable iCloud on the device?

Making sure that you can retrieve a ubiquity container URL forms the first step for iCloud development.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020