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Syncing Preferences

Users can sync application preferences to multiple computers over .Mac. By syncing preferences, the user preserves their application settings when moving from computer to computer similar to the advantages of using a network home directory. The user enables this feature, in a way similar to selecting sync schemas, using the .Mac Sync pane in System Preferences. The user must first configure .Mac and enable syncing before enabling this feature. For many applications this is a convenient mechanism that requires no source code changes. However, if syncing preferences does not make sense for your application, you can turn this feature off for all or selected application preferences. This article describes several approaches to controlling what application preferences are synced.

Contents:

Controlling Syncing Preferences
Excluding Preferences Using the Information Property List
Excluding Preferences Using Preferences or User Defaults

Controlling Syncing Preferences

Set the com.apple.PreferenceSync.ExcludeAllSyncKeys key to true to exclude all your application preferences from syncing. The default value is false—all application preferences are synced.

If you want to exclude just some preferences, set the com.apple.PreferenceSync.ExcludeSyncKeys key to an array of keys that you want to exclude from syncing. The keys are represented by string values and are not localized.

You can either use the application information property list, user defaults, or application preferences to set these keys. The defaults for the preference domain is first checked for these settings. If they are not found in the defaults, the application’s info.plist file is checked. Therefore, if you set these keys programmatically at runtime, you override any values set in the application’s info.plist file.

You can also use preference domains to exclude some keys from being synced. Use preference domains to specify that some application preferences are host-specific and should not be synced. This is recommended for preferences that are intended for a single computer only. Read Preference Domains in Preferences Programming Topics for Core Foundation for more information.

Excluding Preferences Using the Information Property List

Set the com.apple.PreferenceSync.ExcludeAllSyncKeys key to true in the application’s info.plist file to exclude all application preferences from syncing as show in Listing 1.

Listing 1  Excluding all preferences using the information property list

<plist version="1.0">

<dict>

    ...

    <key>com.apple.PreferenceSync.ExcludeAllSyncKeys</key>

    <true/>

</dict>

</plist

Alternatively, exclude selected keys by setting the com.apple.PreferenceSync.ExcludeSyncKeys key to an array of keys in the application’s info.plist file as show in Listing 2.

Listing 2  Excluding selected preferences using the information property list

<plist version="1.0">

<dict>

    ...

    <key>com.apple.PreferenceSync.ExcludeSyncKeys</key>

    <array>

        <string>preferenceX</string>

        <string>preferenceY</string>

    </array>

</dict>

</plist

The advantage of setting these keys in the application’s info.plist file is that your application or an installer doesn’t need to run to set these keys.

Excluding Preferences Using Preferences or User Defaults

In addition, you can set these keys programmatically using application preferences or user defaults.

The following code fragment uses the CFPreferences opaque type to set the com.apple.PreferenceSync.ExcludeAllSyncKeys key to kCFBooleanTrue:

CFPreferencesSetAppValue(CFSTR("com.apple.PreferenceSync.ExcludeAllSyncKeys"), kCFBooleanTrue, kCFPreferencesCurrentApplication);

Read Preferences Programming Topics for Core Foundation to learn more about the CFPreferences opaque type.

The following Objective-C code fragment uses user defaults to exclude all application preferences from syncing by setting the com.apple.PreferenceSync.ExcludeAllSyncKeys key to YES:

[[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithBool:YES] forKey:@"com.apple.PreferenceSync.ExcludeAllSyncKeys"];

Read User Defaults Programming Topics for Cocoa to learn more about the NSUserDefaults class.

You can also set user defaults from the command line. The following command sets the com.apple.PreferenceSync.ExcludeSyncKeys key to exclude the preferenceX and preferenceY preferences from syncing:

defaults write com.apple.myapp com.apple.PreferenceSync.ExcludeSyncKeys -array preferenceX preferenceY

The disadvantage of using preferences or user defaults is that your application or an installer needs to run to set these keys.

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